From 575c4addcebc8c6cff71109d3f648b35aa49910b Mon Sep 17 00:00:00 2001
From: Logan Chien <tzuhsiang.chien@gmail.com>
Date: Wed, 5 Feb 2014 14:15:16 +0000
Subject: [PATCH] ARM: Resolve thumb_bl fixup in same MCFragment.

In Thumb1 mode, bl instruction might be selected for branches between
basic blocks in the function if the offset is greater than 2KB.
However, this might cause SEGV because the destination symbol
is not marked as thumb function and the execution mode will be reset
to ARM mode.

Since we are sure that these symbols are in the same data fragment, we
can simply resolve these local symbols, and don't emit any relocation
information for this bl instruction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200842 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp |  9 ++++++-
 test/MC/ARM/thumb-far-jump.s                  | 26 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 test/MC/ARM/thumb-far-jump.s

diff --git a/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 7db700472cb..698487980c3 100644
--- a/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -565,11 +565,18 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
         Value |= 1;
     }
   }
+  // For Thumb1 BL instruction, it is possible to be a long jump between
+  // the basic blocks of the same function.  Thus, we would like to resolve
+  // the offset when the destination has the same MCFragment.
+  if (A && (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl) {
+    const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
+    MCSymbolData &SymData = Asm.getSymbolData(Sym);
+    IsResolved = (SymData.getFragment() == DF);
+  }
   // We must always generate a relocation for BL/BLX instructions if we have
   // a symbol to reference, as the linker relies on knowing the destination
   // symbol's thumb-ness to get interworking right.
   if (A && ((unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_blx ||
-            (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_blx ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_uncondbl ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_condbl))
diff --git a/test/MC/ARM/thumb-far-jump.s b/test/MC/ARM/thumb-far-jump.s
new file mode 100644
index 00000000000..2fd2c567d13
--- /dev/null
+++ b/test/MC/ARM/thumb-far-jump.s
@@ -0,0 +1,26 @@
+@ RUN: llvm-mc < %s -triple thumbv5-linux-gnueabi -filetype=obj -o - \
+@ RUN:   | llvm-readobj -r | FileCheck %s
+	.syntax	unified
+
+	.text
+	.align	2
+	.globl	main
+	.type	main,%function
+	.thumb_func
+main:
+	bl	end
+	.space 8192
+end:
+	bl	main2
+	bx	lr
+
+	.text
+	.align	2
+	.globl	main2
+	.type	main2,%function
+	.thumb_func
+main2:
+	bx	lr
+
+@ CHECK-NOT: 0x0 R_ARM_THM_CALL end 0x0
+@ CHECK: 0x2004 R_ARM_THM_CALL main2 0x0
-- 
2.34.1