[glibc/google/grte/v5-2.27/master] elf: Support DT_RELR relative relocation format

[Fangrui Song <maskray@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4feaf8a3a84df72b1e61a84a551272cad75bc16d

commit 4feaf8a3a84df72b1e61a84a551272cad75bc16d
Author: Fangrui Song <maskray@google.com>
Date:   Tue Jan 11 16:20:39 2022 -0800

    elf: Support DT_RELR relative relocation format
    
    Upstream patch: https://sourceware.org/pipermail/libc-alpha/2021-October/132029.html
    Bikeshedding: https://sourceware.org/pipermail/libc-alpha/2021-November/133009.html
    
    This commit removes configure.ac and test changes to avoid conflict when
    the upstream finally gets the feature. $(have-relr) is kept for local
    testing.
    
    To work around b/208156916, DT_NUM is not bumped. DT_RELR and DT_RELRSZ
    take the l_info slots at DT_VERSYM+1 and DT_VERSYM+2.

Diff:
---
 elf/Makefile           |  7 +++++++
 elf/dynamic-link.h     | 30 ++++++++++++++++++++++++++++++
 elf/elf.h              | 15 +++++++++++++--
 elf/get-dynamic-info.h |  8 +++++++-
 elf/tst-relr-no-pie.c  |  1 +
 elf/tst-relr.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 103 insertions(+), 3 deletions(-)

diff --git a/elf/Makefile b/elf/Makefile
index 1b9acb5242..6d023d75a0 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -209,6 +209,13 @@ tests-execstack-yes = tst-execstack tst-execstack-needed tst-execstack-prog
 endif
 endif
 endif
+ifeq ($(have-relr),yes)
+tests += tst-relr tst-relr-no-pie
+tests-pie += tst-relr
+tests-no-pie += tst-relr-no-pie
+LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr
+LDFLAGS-tst-relr-no-pie += -Wl,--pack-dyn-relocs=relr -no-pie
+endif
 ifeq ($(run-built-tests),yes)
 tests-special += $(objpfx)tst-leaks1-mem.out \
 		 $(objpfx)tst-leaks1-static-mem.out $(objpfx)noload-mem.out \
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index f576d787e3..5b146d854f 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -253,6 +253,35 @@ elf_machine_lazy_rel (struct link_map *map,
 #  define ELF_DYNAMIC_DO_RELA(map, lazy, skip_ifunc, boot_map) /* Nothing to do.  */
 # endif
 
+/* Google-local: b/208156916.  To not bump DT_NUM, use DT_VERSYM+1 for DT_RELR
+   and DT_VERSYM+2 for DT_RELRSZ.  */
+# 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[VERSYMIDX (DT_VERSYM + 1)])			      \
+      break;								      \
+    r = (const ElfW(Relr) *)D_PTR((map), l_info[VERSYMIDX (DT_VERSYM + 1)]);  \
+    end = (const ElfW(Relr) *)((const char *)r +			      \
+                               (map)->l_info[VERSYMIDX (DT_VERSYM + 2)]->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, lazy, consider_profile, skip_ifunc, boot_map) \
@@ -261,6 +290,7 @@ elf_machine_lazy_rel (struct link_map *map,
 					      (consider_profile));	      \
     ELF_DYNAMIC_DO_REL ((map), edr_lazy, skip_ifunc, boot_map);			\
     ELF_DYNAMIC_DO_RELA ((map), edr_lazy, skip_ifunc, boot_map);			\
+    ELF_DYNAMIC_DO_RELR ((map));					      \
   } while (0)
 #else /* NESTING */
 # if ! ELF_MACHINE_NO_REL
diff --git a/elf/elf.h b/elf/elf.h
index 954f3266f7..35ff17cae2 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -444,8 +444,9 @@ typedef struct
 #define SHT_FINI_ARRAY	  15		/* Array of destructors */
 #define SHT_PREINIT_ARRAY 16		/* Array of pre-constructors */
 #define SHT_GROUP	  17		/* Section group */
-#define SHT_SYMTAB_SHNDX  18		/* Extended section indeces */
-#define	SHT_NUM		  19		/* Number of defined types.  */
+#define SHT_SYMTAB_SHNDX  18		/* Extended section indices */
+#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.  */
@@ -663,6 +664,11 @@ 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)
@@ -861,6 +867,11 @@ typedef struct
 #define DT_ENCODING	32		/* Start of encoded range */
 #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_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 */
+/* Google-local: b/208156916.  Don't bump DT_NUM.  */
 #define	DT_NUM		34		/* Number used */
 #define DT_LOOS		0x6000000d	/* Start of OS-specific */
 #define DT_HIOS		0x6ffff000	/* End of OS-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index f9c5b84d6a..3710d41841 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -49,7 +49,12 @@ elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
 
   while (dyn->d_tag != DT_NULL)
     {
-      if ((d_tag_utype) dyn->d_tag < DT_NUM)
+      /* Google-local: b/208156916.  See ELF_DYNAMIC_DO_RELR.  */
+      if (dyn->d_tag == DT_RELR)
+	info[VERSYMIDX (DT_VERSYM + 1)] = dyn;
+      else if (dyn->d_tag == DT_RELRSZ)
+	info[VERSYMIDX (DT_VERSYM + 2)] = dyn;
+      else if ((d_tag_utype) dyn->d_tag < DT_NUM)
 	info[dyn->d_tag] = dyn;
       else if (dyn->d_tag >= DT_LOPROC &&
 	       dyn->d_tag < DT_LOPROC + DT_THISPROCNUM)
@@ -112,6 +117,7 @@ elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
 # endif
       ADJUST_DYN_INFO (DT_JMPREL);
       ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
+      ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM + 1)); /* DT_RELR */
       ADJUST_DYN_INFO (DT_ADDRTAGIDX (DT_GNU_HASH) + DT_NUM + DT_THISPROCNUM
 		       + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM);
 # undef ADJUST_DYN_INFO
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..22eb8c75a0
--- /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 0;
+	}
+    }
+
+  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>