From b97dac52268053372f19525fc77c87c8c7870e05 Mon Sep 17 00:00:00 2001
From: Tim Northover <tnorthover@apple.com>
Date: Wed, 23 Aug 2017 22:07:10 +0000
Subject: [PATCH] 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311611 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../ARM/MCTargetDesc/ARMMachObjectWriter.cpp   | 13 +++++++++++--
 test/MC/ARM/arm-macho-calls.s                  | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 test/MC/ARM/arm-macho-calls.s

diff --git a/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 6f0372c9019..f371699e9fc 100644
--- a/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -324,8 +324,17 @@ bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
   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;
diff --git a/test/MC/ARM/arm-macho-calls.s b/test/MC/ARM/arm-macho-calls.s
new file mode 100644
index 00000000000..47af47f1f9f
--- /dev/null
+++ b/test/MC/ARM/arm-macho-calls.s
@@ -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
-- 
2.50.1