[PATCH] MIPS/readelf: With `-A' also dump GOT in static binaries

[PATCH] MIPS/readelf: With `-A' also dump GOT in static binaries

[Maciej W. Rozycki]

A static, non-relocated global offset table will be embedded in static 
binaries produced from objects containing any kind of GOT relocations, 
generally PIC code.  All symbols will have been resolved in static link 
in such binaries making all GOT entries local and their values final as
there is no run-time load processing further performed.

Dump such GOT with `readelf -A' like already done with regular GOT, to 
make it easier to examine static code that uses accesses via the GOT 
pointer.  There will be no dynamic segment or section in a static binary 
to get the GOT pointer (DT_PLTGOT) from, so use section headers to find 
a `.got' section instead.

	binutils/
	* readelf.c (process_mips_specific): Add static GOT support.
---
 I will commit this change shortly, once the two outstanding `readelf' 
clean-ups recently posted have been committed that this change is 
conceptually consistent with.

  Maciej

binutils-mips-readelf-arch-static-got.diff
Index: binutils/binutils/readelf.c
===================================================================
--- binutils.orig/binutils/readelf.c	2017-04-10 23:37:14.563833225 +0100
+++ binutils/binutils/readelf.c	2017-04-10 23:40:11.957781646 +0100
@@ -15001,8 +15001,82 @@ process_mips_specific (FILE * file)
 
   /* We have a lot of special sections.  Thanks SGI!  */
   if (dynamic_section == NULL)
-    /* No information available.  */
-    return res;
+    {
+      /* No dynamic information available.  See if there is static GOT.  */
+      sect = find_section (".got");
+      if (sect != NULL)
+	{
+	  unsigned char *data_end;
+	  unsigned char *data;
+	  bfd_vma ent, end;
+	  int addr_size;
+
+	  pltgot = sect->sh_addr;
+
+	  ent = pltgot;
+	  addr_size = (is_32bit_elf ? 4 : 8);
+	  end = pltgot + sect->sh_size;
+
+	  data = (unsigned char *) get_data (NULL, file, sect->sh_offset,
+					     end - pltgot, 1,
+					     _("Global Offset Table data"));
+	  /* PR 12855: Null data is handled gracefully throughout.  */
+	  data_end = data + (end - pltgot);
+
+	  printf (_("\nStatic GOT:\n"));
+	  printf (_(" Canonical gp value: "));
+	  print_vma (ent + 0x7ff0, LONG_HEX);
+	  printf ("\n\n");
+
+	  printf (_(" Reserved entries:\n"));
+	  printf (_("  %*s %10s %*s\n"),
+		  addr_size * 2, _("Address"), _("Access"),
+		  addr_size * 2, _("Value"));
+	  ent = print_mips_got_entry (data, pltgot, ent, data_end);
+	  printf ("\n");
+	  if (ent == (bfd_vma) -1)
+	    goto sgot_print_fail;
+
+	  /* Check for the MSB of GOT[1] being set, identifying a GNU
+	     object.  This entry will be used by some runtime loaders,
+	     to store the module pointer.  Otherwise this is an ordinary
+	     local entry.
+	     PR 21344: Check for the entry being fully available before
+	     fetching it.  */
+	  if (data
+	      && data + ent - pltgot + addr_size <= data_end
+	      && (byte_get (data + ent - pltgot, addr_size)
+		  >> (addr_size * 8 - 1)) != 0)
+	    {
+	      ent = print_mips_got_entry (data, pltgot, ent, data_end);
+	      printf ("\n");
+	      if (ent == (bfd_vma) -1)
+		goto sgot_print_fail;
+	    }
+	  printf ("\n");
+
+	  if (ent < end)
+	    {
+	      printf (_(" Local entries:\n"));
+	      printf ("  %*s %10s %*s\n",
+		      addr_size * 2, _("Address"), _("Access"),
+		      addr_size * 2, _("Value"));
+	      while (ent < end)
+		{
+		  ent = print_mips_got_entry (data, pltgot, ent, data_end);
+		  printf ("\n");
+		  if (ent == (bfd_vma) -1)
+		    goto sgot_print_fail;
+		}
+	      printf ("\n");
+	    }
+
+	sgot_print_fail:
+	  if (data)
+	    free (data);
+	}
+      return res;
+    }
 
   for (entry = dynamic_section;
        /* PR 17531 file: 012-50589-0.004.  */