llvm-project/llvm/lib/Target/X86/X86TargetObjectFile.h

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//===-- X86TargetObjectFile.h - X86 Object Info -----------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIB_TARGET_X86_X86TARGETOBJECTFILE_H
#define LLVM_LIB_TARGET_X86_X86TARGETOBJECTFILE_H
#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
namespace llvm {
/// X86_64MachoTargetObjectFile - This TLOF implementation is used for Darwin
/// x86-64.
class X86_64MachoTargetObjectFile : public TargetLoweringObjectFileMachO {
public:
const MCExpr *
getTTypeGlobalReference(const GlobalValue *GV, unsigned Encoding,
Mangler &Mang, const TargetMachine &TM,
MachineModuleInfo *MMI,
MCStreamer &Streamer) const override;
// getCFIPersonalitySymbol - The symbol that gets passed to
// .cfi_personality.
MCSymbol *getCFIPersonalitySymbol(const GlobalValue *GV, Mangler &Mang,
const TargetMachine &TM,
MachineModuleInfo *MMI) const override;
[AsmPrinter] Access pointers to globals via pcrel GOT entries Front-ends could use global unnamed_addr to hold pointers to other symbols, like @gotequivalent below: @foo = global i32 42 @gotequivalent = private unnamed_addr constant i32* @foo @delta = global i32 trunc (i64 sub (i64 ptrtoint (i32** @gotequivalent to i64), i64 ptrtoint (i32* @delta to i64)) to i32) The global @delta holds a data "PC"-relative offset to @gotequivalent, an unnamed pointer to @foo. The darwin/x86-64 assembly output for this follows: .globl _foo _foo: .long 42 .globl _gotequivalent _gotequivalent: .quad _foo .globl _delta _delta: .long _gotequivalent-_delta Since unnamed_addr indicates that the address is not significant, only the content, we can optimize the case above by replacing pc-relative accesses to "GOT equivalent" globals, by a PC relative access to the GOT entry of the final symbol instead. Therefore, "delta" can contain a pc relative relocation to foo's GOT entry and we avoid the emission of "gotequivalent", yielding the assembly code below: .globl _foo _foo: .long 42 .globl _delta _delta: .long _foo@GOTPCREL+4 There are a couple of advantages of doing this: (1) Front-ends that need to emit a great deal of data to store pointers to external symbols could save space by not emitting such "got equivalent" globals and (2) IR constructs combined with this opt opens a way to represent GOT pcrel relocations by using the LLVM IR, which is something we previously had no way to express. Differential Revision: http://reviews.llvm.org/D6922 rdar://problem/18534217 llvm-svn: 230264
2015-02-24 05:26:18 +08:00
const MCExpr *getIndirectSymViaGOTPCRel(const MCSymbol *Sym,
const MCValue &MV, int64_t Offset,
MachineModuleInfo *MMI,
MCStreamer &Streamer) const override;
};
/// \brief This implemenatation is used for X86 ELF targets that don't
/// have a further specialization.
class X86ELFTargetObjectFile : public TargetLoweringObjectFileELF {
/// \brief Describe a TLS variable address within debug info.
const MCExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const override;
};
/// X86LinuxNaClTargetObjectFile - This implementation is used for linux and
/// Native Client on x86 and x86-64.
class X86LinuxNaClTargetObjectFile : public X86ELFTargetObjectFile {
void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
};
/// \brief This implementation is used for Windows targets on x86 and x86-64.
class X86WindowsTargetObjectFile : public TargetLoweringObjectFileCOFF {
const MCExpr *
getExecutableRelativeSymbol(const ConstantExpr *CE, Mangler &Mang,
const TargetMachine &TM) const override;
/// \brief Given a mergeable constant with the specified size and relocation
/// information, return a section that it should be placed in.
MCSection *getSectionForConstant(SectionKind Kind,
const Constant *C) const override;
};
} // end namespace llvm
#endif