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

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.

2 files changed, 28 insertions, 35 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index f1f0e32..a24957a 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,15 @@
 2020-08-25  Alan Modra  <amodra@gmail.com>
 
+	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.
+
+2020-08-25  Alan Modra  <amodra@gmail.com>
+
 	PR 26419
 	* elf-m10300.c (mn10300_elf_relax_section): Don't attempt access
 	before start of section.
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 66930c0..8fec76e 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