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Handle _GLOBAL_OFFSET_TABLE_ correctly.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116932 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2010-10-20 16:46:08 +00:00
parent 9f608b1919
commit 64e6719ee8
2 changed files with 45 additions and 0 deletions
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27
lib/Target/X86/X86MCCodeEmitter.cpp
View File

@ -18,6 +18,7 @@
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
@ -193,6 +194,25 @@ static bool Is32BitMemOperand(const MCInst &MI, unsigned Op) {
return false;
}
/// StartsWithGlobalOffsetTable - Return true for the simple cases where this
/// expression starts with _GLOBAL_OFFSET_TABLE_. This is a needed to support
/// PIC on ELF i386 as that symbol is magic. We check only simple case that
/// are know to be used: _GLOBAL_OFFSET_TABLE_ by itself or at the start
/// of a binary expression.
static bool StartsWithGlobalOffsetTable(const MCExpr *Expr) {
if (Expr->getKind() == MCExpr::Binary) {
const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(Expr);
Expr = BE->getLHS();
}
if (Expr->getKind() != MCExpr::SymbolRef)
return false;
const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Expr);
const MCSymbol &S = Ref->getSymbol();
return S.getName() == "_GLOBAL_OFFSET_TABLE_";
}
void X86MCCodeEmitter::
EmitImmediate(const MCOperand &DispOp, unsigned Size, MCFixupKind FixupKind,
unsigned &CurByte, raw_ostream &OS,
@ -209,6 +229,13 @@ EmitImmediate(const MCOperand &DispOp, unsigned Size, MCFixupKind FixupKind,
// If we have an immoffset, add it to the expression.
const MCExpr *Expr = DispOp.getExpr();
if (StartsWithGlobalOffsetTable(Expr)) {
// FIXME: We should probably change the FixupKind to a special one so that
// other parts of MC don't have to check the symbol name.
assert(ImmOffset == 0);
ImmOffset = CurByte;
}
// If the fixup is pc-relative, we need to bias the value to be relative to
// the start of the field, not the end of the field.
if (FixupKind == MCFixupKind(X86::reloc_pcrel_4byte) ||

18
test/MC/ELF/global-offset.s Normal file
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@ -0,0 +1,18 @@
// RUN: llvm-mc -filetype=obj -triple i386-pc-linux-gnu %s -o - | elf-dump --dump-section-data | FileCheck %s
// We test that _GLOBAL_OFFSET_TABLE_ will account for the two bytes at the
// start of the addl.
addl $_GLOBAL_OFFSET_TABLE_, %ebx
// CHECK: ('sh_name', 0x00000001) # '.text'
// CHECK-NEXT: ('sh_type',
// CHECK-NEXT: ('sh_flags',
// CHECK-NEXT: ('sh_addr',
// CHECK-NEXT: ('sh_offset',
// CHECK-NEXT: ('sh_size',
// CHECK-NEXT: ('sh_link',
// CHECK-NEXT: ('sh_info',
// CHECK-NEXT: ('sh_addralign',
// CHECK-NEXT: ('sh_entsize',
// CHECK-NEXT: ('_section_data', '81c30200 0000')