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Lu" Cc: libc-alpha@sourceware.org, Joseph Myers Subject: Re: [PATCH v5 1/5] elf: Support DT_RELR relative relocation format [BZ #27924] Message-ID: <20220310184833.m4tfk5kxwz6mvsq2@google.com> References: <20220303045026.4172347-1-hjl.tools@gmail.com> <20220303045026.4172347-2-hjl.tools@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20220303045026.4172347-2-hjl.tools@gmail.com> X-Spam-Status: No, score=-26.1 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH, GIT_PATCH_0, KAM_LOTSOFHASH, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE, URIBL_BLACK, USER_IN_DEF_DKIM_WL, USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 10 Mar 2022 18:48:47 -0000 On 2022-03-02, H.J. Lu wrote: >From: Fangrui Song > >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 > >Changes from the original patch: > >1. Check the linker option, -z pack-relative-relocs, which add a >GLIBC_ABI_DT_RELR symbol version dependency on the shared C library if >it provides a GLIBC_2.XX symbol version. >2. Change make variale to have-dt-relr. >3. Rename tst-relr-no-pie to tst-relr-pie for --disable-default-pie. >4. Use TEST_VERIFY in tst-relr.c. >5. Add the check-tst-relr-pie.out test to check for linker generated >libc.so version dependency on GLIBC_ABI_DT_RELR. >--- > configure | 42 +++++++++++++++++++++++++++ > configure.ac | 10 +++++++ > elf/Makefile | 14 +++++++++ > elf/dynamic-link.h | 34 ++++++++++++++++++++++ > elf/elf.h | 13 +++++++-- > elf/get-dynamic-info.h | 3 ++ > elf/tst-relr-pie.c | 1 + > elf/tst-relr.c | 64 ++++++++++++++++++++++++++++++++++++++++++ > 8 files changed, 179 insertions(+), 2 deletions(-) > create mode 100644 elf/tst-relr-pie.c > create mode 100644 elf/tst-relr.c > >diff --git a/configure b/configure >index 8e5bee775a..9156e29fe9 100755 >--- a/configure >+++ b/configure >@@ -6115,6 +6115,48 @@ $as_echo "$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 <+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_dt_relr=yes >+else >+ libc_cv_dt_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-dt-relr = $libc_cv_dt_relr" >+if test "$libc_cv_dt_relr" = yes; then >+ have_dt_relr=1 >+else >+ have_dt_relr=0 >+fi >+ > { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5 > $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; } > libc_linker_feature=no >diff --git a/configure.ac b/configure.ac >index 87f67d25ec..5c09871fee 100644 >--- a/configure.ac >+++ b/configure.ac >@@ -1367,6 +1367,16 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x], > [libc_cv_depaudit=yes], [libc_cv_depaudit=no]) > LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit]) > >+LIBC_LINKER_FEATURE([-z pack-relative-relocs], >+ [-Wl,-z,pack-relative-relocs], >+ [libc_cv_dt_relr=yes], [libc_cv_dt_relr=no]) >+LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr]) >+if test "$libc_cv_dt_relr" = yes; then >+ have_dt_relr=1 >+else >+ have_dt_relr=0 >+fi >+ > 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..fd462ba315 100644 >--- a/elf/Makefile >+++ b/elf/Makefile >@@ -541,6 +541,14 @@ tests-special += \ > # tests-special > endif > endif >+ifeq ($(have-dt-relr),yes) >+tests += tst-relr tst-relr-pie >+tests-pie += tst-relr-pie >+tests-special += $(objpfx)check-tst-relr-pie.out >+CFLAGS-tst-relr-pie.c += $(pie-ccflag) >+LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs >+LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs >+endif > endif > > ifeq ($(run-built-tests),yes) >@@ -2725,3 +2733,9 @@ $(objpfx)tst-p_align3: $(objpfx)tst-p_alignmod3.so > $(objpfx)tst-p_align3.out: tst-p_align3.sh $(objpfx)tst-p_align3 > $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \ > $(evaluate-test) >+ >+$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie >+ LC_ALL=C $(OBJDUMP) -p $< \ >+ | sed -ne '/required from libc.so/,$$ p' \ >+ | grep GLIBC_ABI_DT_RELR > $@; \ >+ $(evaluate-test) >diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h >index 25dd7ca4f2..5318079bac 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 As mentioned on a binutils thread, ELF_DYNAMIC_DO_RELR needs to be reordered before DL_REL/DO_RELA to help powerpc get the support in the future https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=elf/dynamic-link.h;h=169745f9a409aec7995f7418736ae64bfeebc9d6;hp=25dd7ca4f2eca3c97fdd1649c15e1b5106e70dc1;hb=1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299;hpb=edc696a73a7cb07b1aa68792a845a98d036ee7eb >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-pie.c b/elf/tst-relr-pie.c >new file mode 100644 >index 0000000000..7df0cdbfd6 >--- /dev/null >+++ b/elf/tst-relr-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..56addd2ad4 >--- /dev/null >+++ b/elf/tst-relr.c >@@ -0,0 +1,64 @@ >+/* Basic tests for DT_RELR. >+ 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 >+ . */ >+ >+#include >+#include >+#include >+ >+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 defined __PIE__ || defined __pie__ || defined PIE || defined pie >+ TEST_VERIFY (has_relr); >+#else >+ TEST_VERIFY (!has_relr); >+#endif >+ } >+ >+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++) >+ TEST_VERIFY ((arr[i] == 0 && val[i] == 0) >+ || (arr[i] == &o && val[i] == 1) >+ || (arr[i] == &x && val[i] == 2)); >+ >+ return 0; >+} >+ >+#include >-- >2.35.1 >