[ARM] Incorrect relocation type for Thumb2 b<cond>.w

[peter.smith]

Summary

The Thumb2 conditional branch B<cond>.W has a different encoding (T3) to the unconditional branch B.W (T4) as it needs to record <cond>. As the encoding is different the B<cond>.W is given a different relocation type. ELF for the ARM Architecture 4.6.1.6 Static Thumb32 relocations states that R_ARM_THM_JUMP19 should be used for B<cond>.W. At present the MC layer is using the R_ARM_THM_JUMP24 from B.W.

This is a simple change to make fixup_t2_condbranch use R_ARM_THM_JUMP19 and update the test which is incorrectly expecting R_ARM_THM_JUMP24.

[rengolin]

Good catch Peter! LGTM. Thanks!

PS: ARM ELF ABI 4.6.1.6 (Table 4-13).

[peter.smith]

Thanks, committed in revision r271997

[peter.smith]

Thanks, apologies forgot to close this out on committing (revision r271997 earlier in the week).

lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp

case ARM::fixup_arm_uncondbl:
       }
       break;
     case ARM::fixup_arm_condbl:
     case ARM::fixup_arm_condbranch:
     case ARM::fixup_arm_uncondbranch:
       Type = ELF::R_ARM_JUMP24;
       break;
     case ARM::fixup_t2_condbranch:
+      Type = ELF::R_ARM_THM_JUMP19;
+      break;
     case ARM::fixup_t2_uncondbranch:
       Type = ELF::R_ARM_THM_JUMP24;
       break;
     case ARM::fixup_arm_movt_hi16:
       Type = ELF::R_ARM_MOVT_PREL;
       break;
     case ARM::fixup_arm_movw_lo16:
       Type = ELF::R_ARM_MOVW_PREL_NC;

test/MC/ARM/thumb1-relax-bcc.s

 @ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o %t %s
 @ RUN:    llvm-objdump -d -r -triple thumbv7m-none-eabi %t | FileCheck --check-prefix=CHECK-ELF %s
 
         .global func1
 _func1:
         bne _func2
 @ CHECK-ERROR: unsupported relocation on symbol
 
 @ CHECK-ELF: 7f f4 fe af        bne.w #-4
-@ CHECK-ELF-NEXT: R_ARM_THM_JUMP24 _func2
+@ CHECK-ELF-NEXT: R_ARM_THM_JUMP19 _func2