[ARM] Create relocations for wide Thumb2 unconditional branches.

[fhahn]

Summary

The ARM ELF ABI requires the linker to do interworking for wide branches
from Thumb code to ARM code. The range for Thumb2 unconditional branches
is the same as for BL.

That was pointed out by @peter.smith in the comments for D33436.

[fhahn]

I plan to add support for Thumb2 conditional branches in a separate patch, as they have a different range. I'll also investigate why unnecessary relocations are created for backward branches.

[peter.smith]

I'm happy with this change using the same argument as D33436. Will be worth waiting to see if anyone in a later timezone objects before committing.

[fhahn]

I've just created D33898 , which creates relocations for all unconditional branches to function symbols with different execution mode.

[fhahn]

This was fixed in another patch

lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

if ((unsigned)Fixup.getKind() == FK_Data_4 ||
       (unsigned)Fixup.getKind() == ARM::fixup_arm_movt_hi16 ||
       (unsigned)Fixup.getKind() == ARM::fixup_t2_movw_lo16 ||
       (unsigned)Fixup.getKind() == ARM::fixup_t2_movt_hi16) {
     if (Sym) {
       if (Asm.isThumbFunc(Sym))
         Value |= 1;
     }
   }
-  if (IsResolved && (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl) {
+  if (IsResolved && ((unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl ||
+                     (unsigned)Fixup.getKind() == ARM::fixup_t2_uncondbranch)) {
     assert(Sym && "How did we resolve this?");
 
     // If the symbol is external the linker will handle it.
     // FIXME: Should we handle it as an optimization?
 
     // If the symbol is out of range, produce a relocation and hope the
     // linker can handle it. GNU AS produces an error in this case.
     if (Sym->isExternal() || Value >= 0x400004)

test/MC/ARM/thumb2-wide-branch-fixup.s

+@ RUN: llvm-mc < %s -triple armv7-linux-gnueabi -filetype=obj -o - \
+@ RUN:   | llvm-readobj -r | FileCheck %s
+
+  .code  16
+  .thumb_func
+thumb_caller:
+  b.w internal_arm_fn
+  b.w global_arm_fn
+  b.w global_thumb_fn
+  b.w internal_thumb_fn
+  b.w far_thumb_fn
+
+  .type  internal_arm_fn,%function
+  .code  32
+internal_arm_fn:
+  bx  lr
+
+  .globl  global_arm_fn
+  .type  global_arm_fn,%function
+  .code  32
+global_arm_fn:
+  bx  lr
+
+  .type  internal_thumb_fn,%function
+  .code  16
+  .thumb_func
+internal_thumb_fn:
+  bx  lr
+
+  .globl  global_thumb_fn
+  .type  global_thumb_fn,%function
+  .code  16
+  .thumb_func
+global_thumb_fn:
+  bx  lr
+  .space 0x400004
+
+  .type  far_thumb_fn,%function
+  .code  16
+  .thumb_func
+far_thumb_fn:
+  bx  lr
+
+
+@ CHECK: Section (3) .rel.text
+@ CHECK-NEXT: 0x0 R_ARM_THM_JUMP24 internal_arm_fn 0x0
+@ CHECK-NEXT: 0x4 R_ARM_THM_JUMP24 global_arm_fn 0x0
+@ CHECK-NEXT: 0x8 R_ARM_THM_JUMP24 global_thumb_fn 0x0
+@ CHECK-NEXT: 0x10 R_ARM_THM_JUMP24 far_thumb_fn 0x0
+@ CHECK-NEXT: }