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ARM: Darwin BL/BLX relocations to out-of-range symbols. 

When a BL/BLX references a symbol in the same translation unit that is
out of range, use an external relocation. The linker will use this to
generate a branch island rather than a direct reference, allowing the
relocation to resolve correctly.

rdar://12359919

llvm-svn: 164615
This commit is contained in:
Jim Grosbach 2012-09-25 18:07:17 +00:00
parent 506150a071
commit df8ed71839
2 changed files with 91 additions and 1 deletions
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49
llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
View File

@ -41,6 +41,12 @@ class ARMMachObjectWriter : public MCMachObjectTargetWriter {
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue);
bool requiresExternRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCFragment &Fragment,
unsigned RelocType, const MCSymbolData *SD,
uint64_t FixedValue);
public:
ARMMachObjectWriter(bool Is64Bit, uint32_t CPUType,
uint32_t CPUSubtype)
@ -305,6 +311,46 @@ void ARMMachObjectWriter::RecordARMScatteredRelocation(MachObjectWriter *Writer,
Writer->addRelocation(Fragment->getParent(), MRE);
}
bool ARMMachObjectWriter::requiresExternRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCFragment &Fragment,
unsigned RelocType,
const MCSymbolData *SD,
uint64_t FixedValue) {
// Most cases can be identified purely from the symbol.
if (Writer->doesSymbolRequireExternRelocation(SD))
return true;
int64_t Value = (int64_t)FixedValue; // The displacement is signed.
int64_t Range;
switch (RelocType) {
default:
return false;
case macho::RIT_ARM_Branch24Bit:
// PC pre-adjustment of 8 for these instructions.
Value -= 8;
// ARM BL/BLX has a 25-bit offset.
Range = 0x1ffffff;
break;
case macho::RIT_ARM_ThumbBranch22Bit:
// PC pre-adjustment of 4 for these instructions.
Value -= 4;
// Thumb BL/BLX has a 24-bit offset.
Range = 0xffffff;
}
// BL/BLX also use external relocations when an internal relocation
// would result in the target being out of range. This gives the linker
// enough information to generate a branch island.
const MCSectionData &SymSD = Asm.getSectionData(
SD->getSymbol().getSection());
Value += Writer->getSectionAddress(&SymSD);
Value -= Writer->getSectionAddress(Fragment.getParent());
// If the resultant value would be out of range for an internal relocation,
// use an external instead.
if (Value > Range || Value < -(Range + 1))
return true;
return false;
}
void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
@ -373,7 +419,8 @@ void ARMMachObjectWriter::RecordRelocation(MachObjectWriter *Writer,
}
// Check whether we need an external or internal relocation.
if (Writer->doesSymbolRequireExternRelocation(SD)) {
if (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
FixedValue)) {
IsExtern = 1;
Index = SD->getIndex();

43
llvm/test/MC/MachO/ARM/long-call-branch-island-relocation.s Normal file
View File

@ -0,0 +1,43 @@
@ RUN: llvm-mc -n -triple armv7-apple-darwin10 %s -filetype=obj -o %t.o
@ RUN: macho-dump --dump-section-data < %t.o | FileCheck %s
@ rdar://12359919
.syntax unified
.text
.globl _bar
.align 2
.code 16
.thumb_func _bar
_bar:
push {r7, lr}
mov r7, sp
bl _foo
pop {r7, pc}
_junk:
@ Make the _foo symbol sufficiently far away to force the 'bl' relocation
@ above to be out of range. On Darwin, the assembler deals with this by
@ generating an external relocation so the linker can create a branch
@ island.
.space 20000000
.section __TEXT,initcode,regular,pure_instructions
.globl _foo
.align 2
.code 16
_foo:
push {r7, lr}
mov r7, sp
pop {r7, pc}
@ CHECK: ('_relocations', [
@ CHECK: # Relocation 0
@ CHECK: (('word-0', 0x4),
@ CHECK: ('word-1', 0x6d000002)),
@ CHECK: ])