llvm-6502/lib/Target/X86/X86AsmBackend.cpp
Daniel Dunbar a5f1d57f65 MC/Mach-O/x86_64: Add a new hook for checking whether a particular section can
be diced into atoms, and adjust getAtom() to take this into account.
 - This fixes relocations to symbols in fixed size literal sections, for
   example.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103532 91177308-0d34-0410-b5e6-96231b3b80d8
2010-05-12 00:38:17 +00:00

305 lines
9.9 KiB
C++

//===-- X86AsmBackend.cpp - X86 Assembler Backend -------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Target/TargetAsmBackend.h"
#include "X86.h"
#include "X86FixupKinds.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MachObjectWriter.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetRegistry.h"
#include "llvm/Target/TargetAsmBackend.h"
using namespace llvm;
namespace {
static unsigned getFixupKindLog2Size(unsigned Kind) {
switch (Kind) {
default: assert(0 && "invalid fixup kind!");
case X86::reloc_pcrel_1byte:
case FK_Data_1: return 0;
case FK_Data_2: return 1;
case X86::reloc_pcrel_4byte:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
case FK_Data_4: return 2;
case FK_Data_8: return 3;
}
}
class X86AsmBackend : public TargetAsmBackend {
public:
X86AsmBackend(const Target &T)
: TargetAsmBackend(T) {}
void ApplyFixup(const MCAsmFixup &Fixup, MCDataFragment &DF,
uint64_t Value) const {
unsigned Size = 1 << getFixupKindLog2Size(Fixup.Kind);
assert(Fixup.Offset + Size <= DF.getContents().size() &&
"Invalid fixup offset!");
for (unsigned i = 0; i != Size; ++i)
DF.getContents()[Fixup.Offset + i] = uint8_t(Value >> (i * 8));
}
bool MayNeedRelaxation(const MCInst &Inst,
const SmallVectorImpl<MCAsmFixup> &Fixups) const;
void RelaxInstruction(const MCInstFragment *IF, MCInst &Res) const;
bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const;
};
static unsigned getRelaxedOpcode(unsigned Op) {
switch (Op) {
default:
return Op;
case X86::JAE_1: return X86::JAE_4;
case X86::JA_1: return X86::JA_4;
case X86::JBE_1: return X86::JBE_4;
case X86::JB_1: return X86::JB_4;
case X86::JE_1: return X86::JE_4;
case X86::JGE_1: return X86::JGE_4;
case X86::JG_1: return X86::JG_4;
case X86::JLE_1: return X86::JLE_4;
case X86::JL_1: return X86::JL_4;
case X86::JMP_1: return X86::JMP_4;
case X86::JNE_1: return X86::JNE_4;
case X86::JNO_1: return X86::JNO_4;
case X86::JNP_1: return X86::JNP_4;
case X86::JNS_1: return X86::JNS_4;
case X86::JO_1: return X86::JO_4;
case X86::JP_1: return X86::JP_4;
case X86::JS_1: return X86::JS_4;
}
}
bool X86AsmBackend::MayNeedRelaxation(const MCInst &Inst,
const SmallVectorImpl<MCAsmFixup> &Fixups) const {
for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
// We don't support relaxing anything else currently. Make sure we error out
// if we see a non-constant 1 or 2 byte fixup.
//
// FIXME: We should need to check this here, this is better checked in the
// object writer which should be verifying that any final relocations match
// the expected fixup. However, that code is more complicated and hasn't
// been written yet. See the FIXMEs in MachObjectWriter.cpp.
if ((Fixups[i].Kind == FK_Data_1 || Fixups[i].Kind == FK_Data_2) &&
!isa<MCConstantExpr>(Fixups[i].Value))
report_fatal_error("unexpected small fixup with a non-constant operand!");
// Check for a 1byte pcrel fixup, and enforce that we would know how to
// relax this instruction.
if (unsigned(Fixups[i].Kind) == X86::reloc_pcrel_1byte) {
assert(getRelaxedOpcode(Inst.getOpcode()) != Inst.getOpcode());
return true;
}
}
return false;
}
// FIXME: Can tblgen help at all here to verify there aren't other instructions
// we can relax?
void X86AsmBackend::RelaxInstruction(const MCInstFragment *IF,
MCInst &Res) const {
// The only relaxations X86 does is from a 1byte pcrel to a 4byte pcrel.
unsigned RelaxedOp = getRelaxedOpcode(IF->getInst().getOpcode());
if (RelaxedOp == IF->getInst().getOpcode()) {
SmallString<256> Tmp;
raw_svector_ostream OS(Tmp);
IF->getInst().dump_pretty(OS);
report_fatal_error("unexpected instruction to relax: " + OS.str());
}
Res = IF->getInst();
Res.setOpcode(RelaxedOp);
}
/// WriteNopData - Write optimal nops to the output file for the \arg Count
/// bytes. This returns the number of bytes written. It may return 0 if
/// the \arg Count is more than the maximum optimal nops.
///
/// FIXME this is X86 32-bit specific and should move to a better place.
bool X86AsmBackend::WriteNopData(uint64_t Count, MCObjectWriter *OW) const {
static const uint8_t Nops[16][16] = {
// nop
{0x90},
// xchg %ax,%ax
{0x66, 0x90},
// nopl (%[re]ax)
{0x0f, 0x1f, 0x00},
// nopl 0(%[re]ax)
{0x0f, 0x1f, 0x40, 0x00},
// nopl 0(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopl 0L(%[re]ax)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopw 0L(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopw %cs:0L(%[re]ax,%[re]ax,1)
{0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
// nopl 0(%[re]ax,%[re]ax,1)
// nopw 0(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x44, 0x00, 0x00,
0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
// nopw 0(%[re]ax,%[re]ax,1)
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
// nopw 0(%[re]ax,%[re]ax,1)
// nopl 0L(%[re]ax) */
{0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax)
// nopl 0L(%[re]ax)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
// nopl 0L(%[re]ax)
// nopl 0L(%[re]ax,%[re]ax,1)
{0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}
};
// Write an optimal sequence for the first 15 bytes.
uint64_t OptimalCount = (Count < 16) ? Count : 15;
for (uint64_t i = 0, e = OptimalCount; i != e; i++)
OW->Write8(Nops[OptimalCount - 1][i]);
// Finish with single byte nops.
for (uint64_t i = OptimalCount, e = Count; i != e; ++i)
OW->Write8(0x90);
return true;
}
/* *** */
class ELFX86AsmBackend : public X86AsmBackend {
public:
ELFX86AsmBackend(const Target &T)
: X86AsmBackend(T) {
HasAbsolutizedSet = true;
HasScatteredSymbols = true;
}
MCObjectWriter *createObjectWriter(raw_ostream &OS) const {
return 0;
}
bool isVirtualSection(const MCSection &Section) const {
const MCSectionELF &SE = static_cast<const MCSectionELF&>(Section);
return SE.getType() == MCSectionELF::SHT_NOBITS;;
}
};
class DarwinX86AsmBackend : public X86AsmBackend {
public:
DarwinX86AsmBackend(const Target &T)
: X86AsmBackend(T) {
HasAbsolutizedSet = true;
HasScatteredSymbols = true;
}
bool isVirtualSection(const MCSection &Section) const {
const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
return (SMO.getType() == MCSectionMachO::S_ZEROFILL ||
SMO.getType() == MCSectionMachO::S_GB_ZEROFILL);
}
};
class DarwinX86_32AsmBackend : public DarwinX86AsmBackend {
public:
DarwinX86_32AsmBackend(const Target &T)
: DarwinX86AsmBackend(T) {}
MCObjectWriter *createObjectWriter(raw_ostream &OS) const {
return new MachObjectWriter(OS, /*Is64Bit=*/false);
}
};
class DarwinX86_64AsmBackend : public DarwinX86AsmBackend {
public:
DarwinX86_64AsmBackend(const Target &T)
: DarwinX86AsmBackend(T) {
HasReliableSymbolDifference = true;
}
MCObjectWriter *createObjectWriter(raw_ostream &OS) const {
return new MachObjectWriter(OS, /*Is64Bit=*/true);
}
virtual bool doesSectionRequireSymbols(const MCSection &Section) const {
// Temporary labels in the string literals sections require symbols. The
// issue is that the x86_64 relocation format does not allow symbol +
// offset, and so the linker does not have enough information to resolve the
// access to the appropriate atom unless an external relocation is used. For
// non-cstring sections, we expect the compiler to use a non-temporary label
// for anything that could have an addend pointing outside the symbol.
//
// See <rdar://problem/4765733>.
const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
return SMO.getType() == MCSectionMachO::S_CSTRING_LITERALS;
}
virtual bool isSectionAtomizable(const MCSection &Section) const {
const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
// Fixed sized data sections are uniqued, they cannot be diced into atoms.
switch (SMO.getType()) {
default:
return true;
case MCSectionMachO::S_4BYTE_LITERALS:
case MCSectionMachO::S_8BYTE_LITERALS:
case MCSectionMachO::S_16BYTE_LITERALS:
case MCSectionMachO::S_LITERAL_POINTERS:
case MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS:
case MCSectionMachO::S_LAZY_SYMBOL_POINTERS:
case MCSectionMachO::S_MOD_INIT_FUNC_POINTERS:
case MCSectionMachO::S_MOD_TERM_FUNC_POINTERS:
case MCSectionMachO::S_INTERPOSING:
return false;
}
}
};
}
TargetAsmBackend *llvm::createX86_32AsmBackend(const Target &T,
const std::string &TT) {
switch (Triple(TT).getOS()) {
case Triple::Darwin:
return new DarwinX86_32AsmBackend(T);
default:
return new ELFX86AsmBackend(T);
}
}
TargetAsmBackend *llvm::createX86_64AsmBackend(const Target &T,
const std::string &TT) {
switch (Triple(TT).getOS()) {
case Triple::Darwin:
return new DarwinX86_64AsmBackend(T);
default:
return new ELFX86AsmBackend(T);
}
}