Use the first element of GOT for ld.so addresses

	[BZ #14538]
	* sysdeps/x86_64/dl-machine.h (elf_machine_dynamic): Use the
	first element of the GOT.
	(elf_machine_load_address): Return the difference between
	the runtime address of _DYNAMIC and elf_machine_dynamic ().

3 files changed, 20 insertions, 36 deletions

diff --git a/ChangeLog b/ChangeLog
index ad8f23e37f..c130d9de87 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,8 +1,16 @@
+2012-09-02  H.J. Lu  <hongjiu.lu@intel.com>
+
+	[BZ #14538]
+	* sysdeps/x86_64/dl-machine.h (elf_machine_dynamic): Use the
+	first element of the GOT.
+	(elf_machine_load_address): Return the difference between
+	the runtime address of _DYNAMIC and elf_machine_dynamic ().
+
 2012-09-01  Allan McRae  <allan@archlinux.org>
 
-        [BZ #13412]
-        * configure.in (AWK): Require gawk version 3.0 or later.
-        * configure: Regenerated.
+	[BZ #13412]
+	* configure.in (AWK): Require gawk version 3.0 or later.
+	* configure: Regenerated.
 
 2012-09-01  Joseph Myers  <joseph@codesourcery.com>
 
diff --git a/NEWS b/NEWS
index c10e993a99..e0dcdf4696 100644
--- a/NEWS
+++ b/NEWS
@@ -12,7 +12,7 @@ Version 2.17
   3479, 5400, 6778, 6808, 9685, 11607, 13412, 13717, 13696, 13939, 14042,
   14090, 14166, 14150, 14151, 14154, 14157, 14166, 14173, 14195, 14252,
   14283, 14298, 14303, 14307, 14328, 14331, 14336, 14337, 14347, 14349,
-  14459, 14476, 14505, 14516, 14519, 14532
+  14459, 14476, 14505, 14516, 14519, 14532, 14538
 
 * Support for STT_GNU_IFUNC symbols added for s390 and s390x.
   Optimized versions of memcpy, memset, and memcmp added for System z10 and
diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index 9c27ecffd8..d2654aa04b 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -41,13 +41,9 @@ elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
 static inline ElfW(Addr) __attribute__ ((unused))
 elf_machine_dynamic (void)
 {
-  ElfW(Addr) addr;
-
-  /* This works because we have our GOT address available in the small PIC
-     model.  */
-  addr = (ElfW(Addr)) &_DYNAMIC;
-
-  return addr;
+  /* This produces an IP-relative reloc which is resolved at link time. */
+  extern const ElfW(Addr) _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
+  return _GLOBAL_OFFSET_TABLE_[0];
 }
 
 
@@ -55,31 +51,11 @@ elf_machine_dynamic (void)
 static inline ElfW(Addr) __attribute__ ((unused))
 elf_machine_load_address (void)
 {
-  ElfW(Addr) addr;
-
-  /* The easy way is just the same as on x86:
-       leaq _dl_start, %0
-       leaq _dl_start(%%rip), %1
-       subq %0, %1
-     but this does not work with binutils since we then have
-     a R_X86_64_32S relocation in a shared lib.
-
-     Instead we store the address of _dl_start in the data section
-     and compare it with the current value that we can get via
-     an RIP relative addressing mode.  Note that this is the address
-     of _dl_start before any relocation performed at runtime.  In case
-     the binary is prelinked the resulting "address" is actually a
-     load offset which is zero if the binary was loaded at the address
-     it is prelinked for.  */
-
-  asm ("lea _dl_start(%%rip), %0\n\t"
-       "sub 1f(%%rip), %0\n\t"
-       ".section\t.data.rel.ro\n"
-       "1:\t" ASM_ADDR " _dl_start\n\t"
-       ".previous\n\t"
-       : "=r" (addr) : : "cc");
-
-  return addr;
+  /* Compute the difference between the runtime address of _DYNAMIC as seen
+     by an IP-relative reference, and the link-time address found in the
+     special unrelocated first GOT entry.  */
+  extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
+  return (ElfW(Addr)) &_DYNAMIC - elf_machine_dynamic ();
 }
 
 /* Set up the loaded object described by L so its unrelocated PLT