[PATCH] backends: aarch64 always has _GLOBAL_OFFSET_TABLE_ point to .got[0].

[Mark Wielaard <mjw at redhat dot com>]

Like some other architectures aarch64 has a special rule for the
_GLOBAL_OFFSET_TABLE_ symbol. Even if there is a .plt.got section the symbol
value still points to the start of the .got section. This is also what the
dynamic linker expects.

See https://sourceware.org/ml/libc-ports/2013-06/msg00057.html

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 backends/ChangeLog        |    5 +++++
 backends/aarch64_init.c   |    1 +
 backends/aarch64_symbol.c |   28 ++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 4535789..b9ec896 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,8 @@
+2013-12-19  Mark Wielaard  <mjw@redhat.com>
+
+	* aarch64_init.c (aarch64_init): Hook check_special_symbol.
+	* aarch64_symbol.c (aarch64_check_special_symbol): New function.
+
 2013-12-18  Mark Wielaard  <mjw@redhat.com>
 
 	* s390_initreg.c (s390_set_initial_registers_tid): Use union
diff --git a/backends/aarch64_init.c b/backends/aarch64_init.c
index 749af2a..d663d40 100644
--- a/backends/aarch64_init.c
+++ b/backends/aarch64_init.c
@@ -56,6 +56,7 @@ aarch64_init (elf, machine, eh, ehlen)
   HOOK (eh, core_note);
   HOOK (eh, reloc_simple_type);
   HOOK (eh, return_value_location);
+  HOOK (eh, check_special_symbol);
 
   return MODVERSION;
 }
diff --git a/backends/aarch64_symbol.c b/backends/aarch64_symbol.c
index b0f3377..4e1dbd8 100644
--- a/backends/aarch64_symbol.c
+++ b/backends/aarch64_symbol.c
@@ -32,6 +32,7 @@
 
 #include <elf.h>
 #include <stddef.h>
+#include <string.h>
 
 #define BACKEND		aarch64_
 #include "libebl_CPU.h"
@@ -54,3 +55,30 @@ aarch64_reloc_simple_type (Ebl *ebl __attribute__ ((unused)), int type)
       return ELF_T_NUM;
     }
 }
+
+/* If this is the _GLOBAL_OFFSET_TABLE_ symbol, then it should point to
+   .got[0] even if there is a .got.plt section.  */
+bool
+aarch64_check_special_symbol (Elf *elf, GElf_Ehdr *ehdr, const GElf_Sym *sym,
+                              const char *name, const GElf_Shdr *destshdr)
+{
+  if (name != NULL
+      && strcmp (name, "_GLOBAL_OFFSET_TABLE_") == 0)
+    {
+      const char *sname = elf_strptr (elf, ehdr->e_shstrndx, destshdr->sh_name);
+      if (sname != NULL && strcmp (sname, ".got.plt") == 0)
+	{
+	  Elf_Scn *scn = NULL;
+	  while ((scn = elf_nextscn (elf, scn)) != NULL)
+	    {
+	      GElf_Shdr shdr_mem;
+	      GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
+	      sname = elf_strptr (elf, ehdr->e_shstrndx, shdr->sh_name);
+	      if (name != NULL && strcmp (sname, ".got") == 0)
+		return sym->st_value == shdr->sh_addr;
+	    }
+	}
+    }
+
+  return false;
+}
-- 
1.7.1