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* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2022-03-09 1:20 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2022-03-09 1:20 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299
commit 1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299
Author: Fangrui Song <maskray@google.com>
Date: Tue Mar 8 17:17:05 2022 -0800
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
This patch adds ELF_DYNAMIC_DO_RELR to ELF_DYNAMIC_RELOCATE.
ELF_DYNAMIC_DO_RELR is ordered before ELF_DYNAMIC_DO_REL[A] so that ifunc
resolvers that require relocated got entries have them relocated. This is
needed for ppc64 according to Alan Modra.
Diff:
---
configure | 37 +++++++++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 7 +++++++
elf/dynamic-link.h | 34 ++++++++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 142 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 8e5bee775a..c4e0d9e8e4 100755
--- a/configure
+++ b/configure
@@ -6115,6 +6115,43 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
+$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
+ -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
+ | grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
+ true
+ else
+ libc_linker_feature=yes
+ fi
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 87f67d25ec..d6bb323fa6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1367,6 +1367,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([-z pack-relative-relocs], [-Wl,-z,pack-relative-relocs],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index c96924e9c2..d75353eed0 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -541,6 +541,13 @@ tests-special += \
# tests-special
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -z pack-relative-relocs
+LDFLAGS-tst-relr-no-pie += -z pack-relative-relocs
+endif
endif
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca4f2..169745f9a4 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,12 +146,46 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
+# ifdef RTLD_BOOTSTRAP
+# define DO_RTLD_BOOTSTRAP 1
+# else
+# define DO_RTLD_BOOTSTRAP 0
+# endif
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
do { \
int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
(consider_profile)); \
+ if ((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP) \
+ ELF_DYNAMIC_DO_RELR (map); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
} while (0)
diff --git a/elf/elf.h b/elf/elf.h
index 0735f6b579..0195029188 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6db4..6c2a3a12b1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2022-01-08 8:18 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2022-01-08 8:18 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2cd3aeb9c0a2fbd03b37065e7630a48571bb6b8
commit b2cd3aeb9c0a2fbd03b37065e7630a48571bb6b8
Author: Fangrui Song <maskray@google.com>
Date: Sat Jan 8 00:17:48 2022 -0800
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
To protect mysterious crash when a DT_RELR using object runs with older
glibc, GNU ld's -z pack-relative-relocs adds a version dependency on
libc.so.6's GLIBC_ABI_DT_RELR version node. This change defines
GLIBC_ABI_DT_RELR in libc.so.6.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Changes from v2
* Add GLIBC_ABI_DT_RELR version node similar to HJ Lu's GLIBC_ABI_VERSION_GEN2
https://sourceware.org/pipermail/libc-alpha/2021-November/133386.html
Diff:
---
configure | 37 +++++++++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 19 ++++++++++++++++---
elf/Versions | 3 +++
elf/dynamic-link.h | 34 ++++++++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/libc-abi-dt-relr.c | 21 +++++++++++++++++++++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
scripts/abilist.awk | 2 ++
11 files changed, 177 insertions(+), 5 deletions(-)
diff --git a/configure b/configure
index 3f956cf777..fc6d8d8244 100755
--- a/configure
+++ b/configure
@@ -6102,6 +6102,43 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
+$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
+ -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
+ | grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
+ true
+ else
+ libc_linker_feature=yes
+ fi
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 277d3527d2..9cebe17325 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1361,6 +1361,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([-z pack-relative-relocs], [-Wl,-z,pack-relative-relocs],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index b86d116be9..33c795d62c 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -26,7 +26,7 @@ routines = $(all-dl-routines) dl-support dl-iteratephdr \
dl-addr dl-addr-obj enbl-secure dl-profstub \
dl-origin dl-libc dl-sym dl-sysdep dl-error \
dl-reloc-static-pie libc_early_init rtld_static_init \
- libc-dl_find_object
+ libc-dl_find_object libc-abi-dt-relr
# The core dynamic linking functions are in libc for the static and
# profiled libraries.
@@ -360,6 +360,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out $(objpfx)tst-audit14a-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -z pack-relative-relocs
+LDFLAGS-tst-relr-no-pie += -z pack-relative-relocs
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
@@ -824,8 +831,10 @@ $(eval $(call include_dsosort_tests,dso-sort-tests-1.def))
$(eval $(call include_dsosort_tests,dso-sort-tests-2.def))
endif
-check-abi: $(objpfx)check-abi-ld.out
-tests-special += $(objpfx)check-abi-ld.out
+check-abi: $(objpfx)check-abi-ld.out \
+ $(objpfx)check-libc-abi-dt-relr.out
+tests-special += $(objpfx)check-abi-ld.out \
+ $(objpfx)check-libc-abi-dt-relr.out
update-abi: update-abi-ld
update-all-abi: update-all-abi-ld
@@ -2350,3 +2359,7 @@ CFLAGS-tst-dl_find_object-mod6.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod7.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod8.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod9.c += -funwind-tables
+
+$(objpfx)check-libc-abi-dt-relr.out: $(common-objpfx)libc.so
+ LC_ALL=C $(NM) -D $< | grep '__libc_abi_dt_relr_placeholder@@GLIBC_ABI_DT_RELR' > $@; \
+ $(evaluate-test)
diff --git a/elf/Versions b/elf/Versions
index a4f1e76708..79325817d3 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -23,6 +23,9 @@ libc {
GLIBC_2.35 {
_dl_find_object;
}
+ GLIBC_ABI_DT_RELR {
+ __libc_abi_dt_relr_placeholder;
+ }
GLIBC_PRIVATE {
# functions used in other libraries
__libc_early_init;
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca4f2..4dd62b34d7 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,14 +146,48 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
+# ifdef RTLD_BOOTSTRAP
+# define DO_RTLD_BOOTSTRAP 1
+# else
+# define DO_RTLD_BOOTSTRAP 0
+# endif
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
do { \
int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ if ((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP) \
+ ELF_DYNAMIC_DO_RELR (map); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 0735f6b579..0195029188 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6db4..6c2a3a12b1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/libc-abi-dt-relr.c b/elf/libc-abi-dt-relr.c
new file mode 100644
index 0000000000..41c8e9f8eb
--- /dev/null
+++ b/elf/libc-abi-dt-relr.c
@@ -0,0 +1,21 @@
+/* Placeholder definition for GLIBC_ABI_DT_RELR node.
+ Copyright (C) 2022 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#ifdef SHARED
+const char __libc_abi_dt_relr_placeholder = 0;
+#endif
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/scripts/abilist.awk b/scripts/abilist.awk
index 24a34ccbed..e6a94c6571 100644
--- a/scripts/abilist.awk
+++ b/scripts/abilist.awk
@@ -55,6 +55,8 @@ $2 == "g" || $2 == "w" && (NF == 7 || NF == 8) {
# caused STV_HIDDEN symbols to appear in .dynsym, though that is useless.
if (NF > 7 && $7 == ".hidden") next;
+ if (version == "GLIBC_ABI_DT_RELR") next;
+
if (version == "GLIBC_PRIVATE" && !include_private) next;
desc = "";
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2022-01-08 8:18 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2022-01-08 8:18 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
b2cd3aeb9c... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
0741e8dd93... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
0741e8d... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
b2cd3ae... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2022-01-08 8:15 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2022-01-08 8:15 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0741e8dd9374adfe6872470d9df9d9a0fa8f3166
commit 0741e8dd9374adfe6872470d9df9d9a0fa8f3166
Author: Fangrui Song <maskray@google.com>
Date: Sat Jan 8 00:12:49 2022 -0800
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
To protect mysterious crash when a DT_RELR using object runs with older
glibc, GNU ld's -z pack-relative-relocs adds a version dependency on
libc.so.6's GLIBC_ABI_DT_RELR version node. This change defines
GLIBC_ABI_DT_RELR in libc.so.6.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 37 +++++++++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 19 ++++++++++++++++---
elf/Versions | 3 +++
elf/dynamic-link.h | 34 ++++++++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/libc-abi-dt-relr.c | 21 +++++++++++++++++++++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
scripts/abilist.awk | 2 ++
11 files changed, 177 insertions(+), 5 deletions(-)
diff --git a/configure b/configure
index 3f956cf777..fc6d8d8244 100755
--- a/configure
+++ b/configure
@@ -6102,6 +6102,43 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
+$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
+ -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
+ | grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
+ true
+ else
+ libc_linker_feature=yes
+ fi
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 277d3527d2..9cebe17325 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1361,6 +1361,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([-z pack-relative-relocs], [-Wl,-z,pack-relative-relocs],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index b86d116be9..33c795d62c 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -26,7 +26,7 @@ routines = $(all-dl-routines) dl-support dl-iteratephdr \
dl-addr dl-addr-obj enbl-secure dl-profstub \
dl-origin dl-libc dl-sym dl-sysdep dl-error \
dl-reloc-static-pie libc_early_init rtld_static_init \
- libc-dl_find_object
+ libc-dl_find_object libc-abi-dt-relr
# The core dynamic linking functions are in libc for the static and
# profiled libraries.
@@ -360,6 +360,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out $(objpfx)tst-audit14a-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -z pack-relative-relocs
+LDFLAGS-tst-relr-no-pie += -z pack-relative-relocs
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
@@ -824,8 +831,10 @@ $(eval $(call include_dsosort_tests,dso-sort-tests-1.def))
$(eval $(call include_dsosort_tests,dso-sort-tests-2.def))
endif
-check-abi: $(objpfx)check-abi-ld.out
-tests-special += $(objpfx)check-abi-ld.out
+check-abi: $(objpfx)check-abi-ld.out \
+ $(objpfx)check-libc-abi-dt-relr.out
+tests-special += $(objpfx)check-abi-ld.out \
+ $(objpfx)check-libc-abi-dt-relr.out
update-abi: update-abi-ld
update-all-abi: update-all-abi-ld
@@ -2350,3 +2359,7 @@ CFLAGS-tst-dl_find_object-mod6.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod7.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod8.c += -funwind-tables
CFLAGS-tst-dl_find_object-mod9.c += -funwind-tables
+
+$(objpfx)check-libc-abi-dt-relr.out: $(common-objpfx)libc.so
+ LC_ALL=C $(NM) -D $< | grep '__libc_abi_dt_relr_placeholder@@GLIBC_ABI_DT_RELR' > $@; \
+ $(evaluate-test)
diff --git a/elf/Versions b/elf/Versions
index a4f1e76708..79325817d3 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -23,6 +23,9 @@ libc {
GLIBC_2.35 {
_dl_find_object;
}
+ GLIBC_ABI_DT_RELR {
+ __libc_abi_dt_relr_placeholder;
+ }
GLIBC_PRIVATE {
# functions used in other libraries
__libc_early_init;
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca4f2..4dd62b34d7 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,14 +146,48 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
+# ifdef RTLD_BOOTSTRAP
+# define DO_RTLD_BOOTSTRAP 1
+# else
+# define DO_RTLD_BOOTSTRAP 0
+# endif
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
do { \
int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ if ((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP) \
+ ELF_DYNAMIC_DO_RELR (map); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 0735f6b579..0195029188 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6db4..6c2a3a12b1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/libc-abi-dt-relr.c b/elf/libc-abi-dt-relr.c
new file mode 100644
index 0000000000..41c8e9f8eb
--- /dev/null
+++ b/elf/libc-abi-dt-relr.c
@@ -0,0 +1,21 @@
+/* Placeholder definition for GLIBC_ABI_DT_RELR node.
+ Copyright (C) 2022 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#ifdef SHARED
+const char __libc_abi_dt_relr_placeholder = 0;
+#endif
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/scripts/abilist.awk b/scripts/abilist.awk
index 24a34ccbed..e6a94c6571 100644
--- a/scripts/abilist.awk
+++ b/scripts/abilist.awk
@@ -55,6 +55,8 @@ $2 == "g" || $2 == "w" && (NF == 7 || NF == 8) {
# caused STV_HIDDEN symbols to appear in .dynsym, though that is useless.
if (NF > 7 && $7 == ".hidden") next;
+ if (version == "GLIBC_ABI_DT_RELR") next;
+
if (version == "GLIBC_PRIVATE" && !include_private) next;
desc = "";
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2022-01-05 3:26 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2022-01-05 3:26 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c1d87463396e9dbb244c1c3467c0e7a4a683221e
commit c1d87463396e9dbb244c1c3467c0e7a4a683221e
Author: Fangrui Song <maskray@google.com>
Date: Tue Jan 4 18:41:03 2022 -0800
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 7 +++++++
elf/dynamic-link.h | 34 ++++++++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 136 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3f956cf777..3329aa6c45 100755
--- a/configure
+++ b/configure
@@ -6102,6 +6102,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 277d3527d2..3bb529b51c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1361,6 +1361,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index b86d116be9..43d57c5e98 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -360,6 +360,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out $(objpfx)tst-audit14a-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca4f2..4dd62b34d7 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,14 +146,48 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
+# ifdef RTLD_BOOTSTRAP
+# define DO_RTLD_BOOTSTRAP 1
+# else
+# define DO_RTLD_BOOTSTRAP 0
+# endif
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
do { \
int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ if ((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP) \
+ ELF_DYNAMIC_DO_RELR (map); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 08b0a97397..f2a172bc4f 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6db4..6c2a3a12b1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-11-19 21:03 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-11-19 21:03 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a9a1b30a4856bbac8d3ba40ac0beb55c64dfe624
commit a9a1b30a4856bbac8d3ba40ac0beb55c64dfe624
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 12:47:16 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 7 +++++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 130 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 2f9adca064..383a0e5ad3 100755
--- a/configure
+++ b/configure
@@ -6071,6 +6071,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 7eb4239359..a8e81849ac 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index 4723c159cb..b9377aaaab 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -251,6 +251,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index f619615e5c..2b7da802fc 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,6 +146,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -154,6 +181,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index f63e07dc6d..005c48d642 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-29 22:21 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-29 22:21 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8e6f8427bdd95a76036c2ac1b97877861df83268
commit 8e6f8427bdd95a76036c2ac1b97877861df83268
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 12:47:16 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 7 +++++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 130 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 2f9adca064..383a0e5ad3 100755
--- a/configure
+++ b/configure
@@ -6071,6 +6071,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 7eb4239359..a8e81849ac 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index cb9bcfb799..a9bfd65b77 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index f63e07dc6d..005c48d642 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 19:50 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 19:50 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3d16f062ba1e6689a0744d009f0b369e6386b378
commit 3d16f062ba1e6689a0744d009f0b369e6386b378
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 12:47:16 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 7 +++++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 130 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..87df6ea5ac 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,13 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 19:49 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 19:49 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
3d16f062ba... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
e62bfdb731... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
e62bfdb... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
3d16f06... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 19:01 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 19:01 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e62bfdb731043e3d1c60593ab9c3aae6d0ae028a
commit e62bfdb731043e3d1c60593ab9c3aae6d0ae028a
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 12:00:44 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 6 ++++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-no-pie.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 129 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..f6550dfef2 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,12 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 19:00 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 19:00 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
e62bfdb731... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
ee9687b1b5... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
ee9687b... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
e62bfdb... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 18:55 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 18:55 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ee9687b1b5114891857a67e6ec4f440b17d03244
commit ee9687b1b5114891857a67e6ec4f440b17d03244
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 11:55:07 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 6 ++++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr-static.c | 1 +
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 129 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..071e5823b2 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,12 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr
+tests-static += tst-relr-static
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-static += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr-static.c b/elf/tst-relr-static.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-static.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 18:55 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 18:55 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
ee9687b1b5... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
a6218e105b... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
a6218e1... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
ee9687b... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 17:57 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 17:57 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a6218e105b40e2d3e24b6eabf8b220175460ed57
commit a6218e105b40e2d3e24b6eabf8b220175460ed57
Author: Fangrui Song <maskray@google.com>
Date: Mon Oct 18 10:52:03 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 4 ++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 126 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..2c4cdfac68 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,10 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..0b0fe5ed17
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,45 @@
+#include <link.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ ElfW(Dyn) *d = _DYNAMIC;
+ if (d)
+ {
+ bool has_relr = false;
+ for (; d->d_tag != DT_NULL; d++)
+ if (d->d_tag == DT_RELR)
+ has_relr = true;
+ if (!has_relr)
+ {
+ fprintf (stderr, "no DT_RELR\n");
+ return 1;
+ }
+ }
+
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-18 17:57 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-18 17:57 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
a6218e105b... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
c22f971f69... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
c22f971... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
a6218e1... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-17 0:49 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-17 0:49 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c22f971f6914d3931c7d1ca20a88680c960c25db
commit c22f971f6914d3931c7d1ca20a88680c960c25db
Author: Fangrui Song <maskray@google.com>
Date: Sat Oct 16 17:48:14 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.
---
Notes I will not include in the submitted commit:
"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.
* Chrome OS folks have carried a local patch since 2018 (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:
* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
Tested on aarch64 and x86_64.
Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html)
* Fix style, simplify code
* Improve test
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 4 ++++
elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr.c | 27 +++++++++++++++++++++++++++
7 files changed, 108 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..2c4cdfac68 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,10 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..fafd42f918 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r, *end; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; r++) \
+ { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) \
+ { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } \
+ else \
+ { \
+ for (long i = 0; (entry >>= 1) != 0; i++) \
+ if ((entry & 1) != 0) \
+ where[i] += l_addr; \
+ where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..79736a4a8a
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,27 @@
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-17 0:49 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-17 0:49 UTC (permalink / raw)
To: glibc-cvs
The branch 'maskray/relr' was updated to point to:
c22f971f69... elf: Support DT_RELR relative relocation format [BZ #27924]
It previously pointed to:
fce13bcfa1... elf: Support DT_RELR relative relocation format [BZ #27924]
Diff:
!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------
fce13bc... elf: Support DT_RELR relative relocation format [BZ #27924]
Summary of changes (added commits):
-----------------------------------
c22f971... elf: Support DT_RELR relative relocation format [BZ #27924]
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-16 20:20 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-16 20:20 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=fce13bcfa150cf9dcefdc1dccf72e025b16d2359
commit fce13bcfa150cf9dcefdc1dccf72e025b16d2359
Author: Fangrui Song <maskray@google.com>
Date: Sat Oct 16 13:18:02 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIC objects (especially PIE and symbolic shared objects) usually have many
relative relocations. In 2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard.
This packed format can typically save 95% dynamic relocation section
size for PIE. The vaddr size of a PIE can be 10% smaller.
* Chrome OS folks have carried a local patch for a while (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports DT_RELR.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions.
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports.
I have adjusted aclocal.m4, otherwise it thinks ld.lld doesn't support
--pack-dyn-relocs=relr just because ld.lld -v --help doesn't contain the literal
string.
% ld.lld -v --help | grep pack-dyn-relocs
--pack-dyn-relocs=[none,android,relr,android+relr]
(`$gnu_ld` is a lie: both gold and ld.lld's "User-Agent:" strings contain
"GNU" and therefore make gnu_ld=true.)
Tested on aarch64 and x86_64.
Diff:
---
configure | 31 +++++++++++++++++++++++++++++++
configure.ac | 4 ++++
elf/Makefile | 4 ++++
elf/dynamic-link.h | 25 +++++++++++++++++++++++++
elf/elf.h | 13 +++++++++++--
elf/get-dynamic-info.h | 3 +++
elf/tst-relr.c | 27 +++++++++++++++++++++++++++
7 files changed, 105 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 3227e434d3..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index bf45d8ee24..2c4cdfac68 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -245,6 +245,10 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \
$(objpfx)tst-audit16-cmp.out
endif
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index ac4cc70dea..ced1c596be 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -160,6 +160,30 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
+ const ElfW(Relr) *r = 0, *end = 0; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
+ end = (const ElfW(Relr) *)((const char *)r + \
+ (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; ++r) { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) { \
+ where = (ElfW(Addr) *)(l_addr + entry); \
+ *where++ += l_addr; \
+ } else { \
+ long i = 0; \
+ for (; (entry >>= 1) != 0; i++) \
+ if (entry % 2 != 0) \
+ where[i] += l_addr; \
+ where += 8 * sizeof(ElfW(Relr)) - 1; \
+ } \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -168,6 +192,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..6dc1ee0ac0 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
+#define DT_RELR 36 /* Address of RELR relative relocations */
+#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 1ac0663d1f..ce0151c2b4 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..79736a4a8a
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,27 @@
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if (!((arr[i] == 0 && val[i] == 0) ||
+ (arr[i] == &o && val[i] == 1) ||
+ (arr[i] == &x && val[i] == 2)))
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
* [glibc/maskray/relr] elf: Support DT_RELR relative relocation format [BZ #27924]
@ 2021-10-08 19:36 Fangrui Song
0 siblings, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2021-10-08 19:36 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=57cb96ba7369984df7ef24c1a108af26eb03c9a6
commit 57cb96ba7369984df7ef24c1a108af26eb03c9a6
Author: Fangrui Song <maskray@google.com>
Date: Thu Oct 7 23:56:39 2021 -0700
elf: Support DT_RELR relative relocation format [BZ #27924]
PIC objects (especially PIE and symbolic shared objects) usually have many
relative relocations. In 2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and welcomed by many parties
(including Solaris). This packed format can typically save 95% dynamic
relocation section size for PIE. The vaddr size of a PIE can be 10% smaller.
* Chrome OS folks have carried a local patch for a while (latest version:
https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
I.e. this feature has been battle tested.
* Android bionic supports DT_RELR.
* The Linux kernel has supported CONFIG_RELR since 2019-08
(https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
https://www.openwall.com/lists/musl/2019/03/06/3
I believe upstream glibc should support DT_RELR to benefit all Linux
distributions.
As of linker support (to the best of my knowledge):
* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
I wish that GNU ld and gold maintainers can implement the feature as well :)
This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports.
I have adjusted aclocal.m4, otherwise it thinks ld.lld doesn't support
--pack-dyn-relocs=relr just because ld.lld -v --help doesn't contain the literal
string.
% ld.lld -v --help | grep pack-dyn-relocs
--pack-dyn-relocs=[none,android,relr,android+relr]
(`$gnu_ld` is a lie: both gold and ld.lld's "User-Agent:" strings contain
"GNU" and therefore make gnu_ld=true.)
Tested on aarch64 and x86_64.
Diff:
---
aclocal.m4 | 19 ++++-----
configure | 107 +++++++++++++++++++++++++++++--------------------
configure.ac | 4 ++
elf/Makefile | 4 ++
elf/dynamic-link.h | 28 +++++++++++++
elf/elf.h | 13 +++++-
elf/get-dynamic-info.h | 3 ++
elf/tst-relr.c | 20 +++++++++
8 files changed, 141 insertions(+), 57 deletions(-)
diff --git a/aclocal.m4 b/aclocal.m4
index c195c4db56..65a12df047 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -224,20 +224,17 @@ AC_DEFUN([LIBC_LINKER_FEATURE],
[AC_MSG_CHECKING([for linker that supports $1])
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
- libc_linker_check=`$LD -v --help 2>/dev/null | grep "\$1"`
- if test -n "$libc_linker_check"; then
- cat > conftest.c <<EOF
+ cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
- $2 -nostdlib -nostartfiles
- -fPIC -shared -o conftest.so conftest.c
- 1>&AS_MESSAGE_LOG_FD])
- then
- libc_linker_feature=yes
- fi
- rm -f conftest*
+ if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ $2 -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&AS_MESSAGE_LOG_FD])
+ then
+ libc_linker_feature=yes
fi
+ rm -f conftest*
fi
if test $libc_linker_feature = yes; then
$3
diff --git a/configure b/configure
index 39d75eb4ed..fdab6a97ef 100755
--- a/configure
+++ b/configure
@@ -5979,25 +5979,22 @@ fi
$as_echo_n "checking for linker that supports -z execstack... " >&6; }
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
- libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z execstack"`
- if test -n "$libc_linker_check"; then
- cat > conftest.c <<EOF
+ cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
- -Wl,-z,execstack -nostdlib -nostartfiles
- -fPIC -shared -o conftest.so conftest.c
- 1>&5'
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,execstack -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
- then
- libc_linker_feature=yes
- fi
- rm -f conftest*
+ then
+ libc_linker_feature=yes
fi
+ rm -f conftest*
fi
if test $libc_linker_feature = yes; then
libc_cv_z_execstack=yes
@@ -6012,25 +6009,22 @@ $as_echo "$libc_linker_feature" >&6; }
$as_echo_n "checking for linker that supports -z start-stop-gc... " >&6; }
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
- libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
- if test -n "$libc_linker_check"; then
- cat > conftest.c <<EOF
+ cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
- -Wl,-z,start-stop-gc -nostdlib -nostartfiles
- -fPIC -shared -o conftest.so conftest.c
- 1>&5'
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,start-stop-gc -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
- then
- libc_linker_feature=yes
- fi
- rm -f conftest*
+ then
+ libc_linker_feature=yes
fi
+ rm -f conftest*
fi
if test $libc_linker_feature = yes; then
libc_cv_z_start_stop_gc=yes
@@ -6046,25 +6040,22 @@ have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
$as_echo_n "checking for linker that supports --depaudit... " >&6; }
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
- libc_linker_check=`$LD -v --help 2>/dev/null | grep "\--depaudit"`
- if test -n "$libc_linker_check"; then
- cat > conftest.c <<EOF
+ cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
- -Wl,--depaudit,x -nostdlib -nostartfiles
- -fPIC -shared -o conftest.so conftest.c
- 1>&5'
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--depaudit,x -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
- then
- libc_linker_feature=yes
- fi
- rm -f conftest*
+ then
+ libc_linker_feature=yes
fi
+ rm -f conftest*
fi
if test $libc_linker_feature = yes; then
libc_cv_depaudit=yes
@@ -6076,29 +6067,57 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5
+$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--pack-dyn-relocs=relr -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }
+ then
+ libc_linker_feature=yes
+ fi
+ rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_relr=yes
+else
+ libc_cv_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-relr = $libc_cv_relr"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
- libc_linker_check=`$LD -v --help 2>/dev/null | grep "\--no-dynamic-linker"`
- if test -n "$libc_linker_check"; then
- cat > conftest.c <<EOF
+ cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
- if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
- -Wl,--no-dynamic-linker -nostdlib -nostartfiles
- -fPIC -shared -o conftest.so conftest.c
- 1>&5'
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,--no-dynamic-linker -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
- then
- libc_linker_feature=yes
- fi
- rm -f conftest*
+ then
+ libc_linker_feature=yes
fi
+ rm -f conftest*
fi
if test $libc_linker_feature = yes; then
libc_cv_no_dynamic_linker=yes
diff --git a/configure.ac b/configure.ac
index 00f49f09f7..96110f9d7d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
+LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr],
+ [libc_cv_relr=yes], [libc_cv_relr=no])
+LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index 26986c0692..e7c3f3404b 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -241,6 +241,10 @@ endif
ifeq ($(have-depaudit),yes)
tests += tst-audit14 tst-audit15 tst-audit16
endif
+ifeq ($(have-relr),yes)
+tests += tst-relr
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+endif
endif
tests += $(tests-execstack-$(have-z-execstack))
ifeq ($(run-built-tests),yes)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 7cc3021164..ce8d628ca1 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -192,6 +192,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
+# define ELF_DYNAMIC_DO_RELR(map) \
+ do { \
+ ElfW(Addr) l_addr = (map)->l_addr, base = 0, start; \
+ const ElfW(Relr) *r = 0, *end = 0; \
+ if (!(map)->l_info[DT_RELR]) \
+ break; \
+ start = D_PTR((map), l_info[DT_RELR]); \
+ r = (const ElfW(Relr) *)start; \
+ end = (const ElfW(Relr) *)(start + (map)->l_info[DT_RELRSZ]->d_un.d_val); \
+ for (; r < end; ++r) { \
+ ElfW(Relr) entry = *r; \
+ if ((entry & 1) == 0) { \
+ *((ElfW(Addr) *)(l_addr + entry)) += l_addr; \
+ base = entry + sizeof(ElfW(Addr)); \
+ continue; \
+ } \
+ ElfW(Addr) offset = base; \
+ do { \
+ entry >>= 1; \
+ if ((entry & 1) != 0) \
+ *((ElfW(Addr) *)(l_addr + offset)) += l_addr; \
+ offset += sizeof(ElfW(Addr)); \
+ } while (entry != 0); \
+ base += (8 * sizeof(ElfW(Relr)) - 1) * sizeof(ElfW(Addr)); \
+ } \
+ } while (0);
+
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
@@ -200,6 +227,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
(consider_profile)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ ELF_DYNAMIC_DO_RELR ((map)); \
} while (0)
#endif
diff --git a/elf/elf.h b/elf/elf.h
index 50f87baceb..093d69fd07 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
-#define SHT_NUM 19 /* Number of defined types. */
+#define SHT_RELR 19 /* RELR relative relocations */
+#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
+/* RELR relocation table entry */
+
+typedef Elf32_Word Elf32_Relr;
+typedef Elf64_Xword Elf64_Relr;
+
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
-#define DT_NUM 35 /* Number used */
+#define DT_RELRSZ 35
+#define DT_RELR 36
+#define DT_RELRENT 37
+#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 15c316b38c..08e3aae68b 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -87,6 +87,7 @@ elf_get_dynamic_info (struct link_map *l)
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
+ ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -111,6 +112,8 @@ elf_get_dynamic_info (struct link_map *l)
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
+ if (info[DT_RELR] != NULL)
+ assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
#ifdef RTLD_BOOTSTRAP
/* Only the bind now flags are allowed. */
assert (info[VERSYMIDX (DT_FLAGS_1)] == NULL
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..20a1409a6c
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,20 @@
+static int o, x;
+void *arr[] = {
+ &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o, &o,
+ 0,
+ &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x, &x,
+};
+
+static int
+do_test (void)
+{
+ for (int i = 0; i < 16; i++)
+ if (arr[i] != &o)
+ return 1;
+ for (int i = 17; i < 33; i++)
+ if (arr[i] != &x)
+ return 1;
+ return 0;
+}
+
+#include <support/test-driver.c>
^ permalink raw reply [flat|nested] 19+ messages in thread
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