[llvm] r311611 - ARM: use internal relocations for local symbols after all.

[Tim Northover via llvm-commits]

Author: tnorthover
Date: Wed Aug 23 15:07:10 2017
New Revision: 311611

URL: http://llvm.org/viewvc/llvm-project?rev=311611&view=rev
Log:
ARM: use internal relocations for local symbols after all.

Switching to external relocations for ARM-mode branches (to allow Thumb
interworking when the offset is unencodable) causes calls to temporary symbols
to be miscompiled and instead go to the parent externally visible symbol.

Calling a temporary never happens in compiled code, but can occasionally in
hand-written assembly.

Added:
    llvm/trunk/test/MC/ARM/arm-macho-calls.s
Modified:
    llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp

Modified: llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp?rev=311611&r1=311610&r2=311611&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp (original)
+++ llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp Wed Aug 23 15:07:10 2017
@@ -324,8 +324,17 @@ bool ARMMachObjectWriter::requiresExtern
   case MachO::ARM_RELOC_BR24:
     // An ARM call might be to a Thumb function, in which case the offset may
     // not be encodable in the instruction and we must use an external
-    // relocation that explicitly mentions the function.
-    return true;
+    // relocation that explicitly mentions the function. Not a problem if it's
+    // to a temporary "Lwhatever" symbol though, and in fact trying to use an
+    // external relocation there causes more issues.
+    if (!S.isTemporary())
+       return true;
+
+    // PC pre-adjustment of 8 for these instructions.
+    Value -= 8;
+    // ARM BL/BLX has a 25-bit offset.
+    Range = 0x1ffffff;
+    break;
   case MachO::ARM_THUMB_RELOC_BR22:
     // PC pre-adjustment of 4 for these instructions.
     Value -= 4;

Added: llvm/trunk/test/MC/ARM/arm-macho-calls.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ARM/arm-macho-calls.s?rev=311611&view=auto
==============================================================================
--- llvm/trunk/test/MC/ARM/arm-macho-calls.s (added)
+++ llvm/trunk/test/MC/ARM/arm-macho-calls.s Wed Aug 23 15:07:10 2017
@@ -0,0 +1,18 @@
+@ RUN: llvm-mc -triple armv7-apple-ios -filetype=obj -o %t %s
+@ RUN: llvm-objdump -d -r %t | FileCheck %s
+
+@ CHECK: _func:
+@ CHECK:    bl #0 <_func+0x8>
+@ CHECK:  ARM_RELOC_BR24 __text
+@ CHECK:    bl #-12 <_func>
+@ CHECK:  ARM_RELOC_BR24 _elsewhere
+    .global _func
+_func:
+    bl Llocal_symbol
+    bl _elsewhere
+Llocal_symbol:
+    bx lr
+
+    .global _elsewhere
+_elsewhere:
+    bx lr