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 ().

1 files changed, 8 insertions, 32 deletions

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