PR26422, ASAN: elf32_arm_final_link_relocate elf32-arm.c:10351

PR26422, ASAN: elf32_arm_final_link_relocate elf32-arm.c:10351

[Alan Modra]

Always reading 32 bits in order to extract addends from instruction
fields is wrong when the field size is smaller.  It also leads to
reading past the end of the section.  This patch tidies that by
reading the proper field size, which allows some later refetching of
addends to disappear.

	PR 26422
	* elf32-arm.c (elf32_arm_final_link_relocate): Use the appropriate
	bfd_get_x size function to read addends out of fields.  Apply
	rightshift adjustment too.  Don't apply the now unnecessary
	howto->size shift to branch REL addends.  Don't refetch R_ARM_ABS8
	and R_ARM_ABS16 addends.  Don't refetch thumb branch addends.
	Correct R_ARM_THM_JUMP6 addend.

diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 66930c0c7d..8fec76e4e1 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -10348,16 +10348,22 @@ elf32_arm_final_link_relocate (reloc_howto_type *	    howto,
 
   if (globals->use_rel)
     {
-      addend = bfd_get_32 (input_bfd, hit_data) & howto->src_mask;
+      bfd_vma sign;
 
-      if (addend & ((howto->src_mask + 1) >> 1))
+      switch (howto->size)
 	{
-	  signed_addend = -1;
-	  signed_addend &= ~ howto->src_mask;
-	  signed_addend |= addend;
+	case 0: addend = bfd_get_8 (input_bfd, hit_data); break;
+	case 1: addend = bfd_get_16 (input_bfd, hit_data); break;
+	case 2: addend = bfd_get_32 (input_bfd, hit_data); break;
+	default: addend = 0; break;
 	}
-      else
-	signed_addend = addend;
+      /* Note: the addend and signed_addend calculated here are
+	 incorrect for any split field.  */
+      addend &= howto->src_mask;
+      sign = howto->src_mask & ~(howto->src_mask >> 1);
+      signed_addend = (addend ^ sign) - sign;
+      signed_addend = (bfd_vma) signed_addend << howto->rightshift;
+      addend <<= howto->rightshift;
     }
   else
     addend = signed_addend = rel->r_addend;
@@ -10752,11 +10758,7 @@ elf32_arm_final_link_relocate (reloc_howto_type *	    howto,
 	  value -= (input_section->output_section->vma
 		    + input_section->output_offset);
 	  value -= rel->r_offset;
-	  if (globals->use_rel)
-	    value += (signed_addend << howto->size);
-	  else
-	    /* RELA addends do not have to be adjusted by howto->size.  */
-	    value += signed_addend;
+	  value += signed_addend;
 
 	  signed_addend = value;
 	  signed_addend >>= howto->rightshift;
@@ -10860,9 +10862,6 @@ elf32_arm_final_link_relocate (reloc_howto_type *	    howto,
       return bfd_reloc_ok;
 
     case R_ARM_ABS8:
-      /* PR 16202: Refectch the addend using the correct size.  */
-      if (globals->use_rel)
-	addend = bfd_get_8 (input_bfd, hit_data);
       value += addend;
 
       /* There is no way to tell whether the user intended to use a signed or
@@ -10875,9 +10874,6 @@ elf32_arm_final_link_relocate (reloc_howto_type *	    howto,
       return bfd_reloc_ok;
 
     case R_ARM_ABS16:
-      /* PR 16202: Refectch the addend using the correct size.  */
-      if (globals->use_rel)
-	addend = bfd_get_16 (input_bfd, hit_data);
       value += addend;
 
       /* See comment for R_ARM_ABS8.  */
@@ -11356,25 +11352,12 @@ elf32_arm_final_link_relocate (reloc_howto_type *	    howto,
 
 	/* CZB cannot jump backward.  */
 	if (r_type == R_ARM_THM_JUMP6)
-	  reloc_signed_min = 0;
-
-	if (globals->use_rel)
 	  {
-	    /* Need to refetch addend.  */
-	    addend = bfd_get_16 (input_bfd, hit_data) & howto->src_mask;
-	    if (addend & ((howto->src_mask + 1) >> 1))
-	      {
-		signed_addend = -1;
-		signed_addend &= ~ howto->src_mask;
-		signed_addend |= addend;
-	      }
-	    else
-	      signed_addend = addend;
-	    /* The value in the insn has been right shifted.  We need to
-	       undo this, so that we can perform the address calculation
-	       in terms of bytes.  */
-	    signed_addend <<= howto->rightshift;
+	    reloc_signed_min = 0;
+	    if (globals->use_rel)
+	      signed_addend = ((addend & 0x200) >> 3) | ((addend & 0xf8) >> 2);
 	  }
+
 	relocation = value + signed_addend;
 
 	relocation -= (input_section->output_section->vma

-- 
Alan Modra
Australia Development Lab, IBM