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llvm-project/llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp

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//===-- X86MachObjectWriter.cpp - X86 Mach-O Writer -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/X86FixupKinds.h"
#include "MCTargetDesc/X86MCTargetDesc.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCValue.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Object/MachOFormat.h"
using namespace llvm;
using namespace llvm::object;
namespace {
class X86MachObjectWriter : public MCMachObjectTargetWriter {
void RecordScatteredRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
unsigned Log2Size,
uint64_t &FixedValue);
void RecordTLVPRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue);
void RecordX86Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue);
void RecordX86_64Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue);
public:
X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
uint32_t CPUSubtype)
: MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
/*UseAggressiveSymbolFolding=*/Is64Bit) {}
void RecordRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue) {
if (Writer->is64Bit())
RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
FixedValue);
else
RecordX86Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
FixedValue);
}
};
}
static bool isFixupKindRIPRel(unsigned Kind) {
return Kind == X86::reloc_riprel_4byte ||
Kind == X86::reloc_riprel_4byte_movq_load;
}
static unsigned getFixupKindLog2Size(unsigned Kind) {
switch (Kind) {
default:
llvm_unreachable("invalid fixup kind!");
case FK_PCRel_1:
case FK_Data_1: return 0;
case FK_PCRel_2:
case FK_Data_2: return 1;
case FK_PCRel_4:
// FIXME: Remove these!!!
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
case X86::reloc_signed_4byte:
case FK_Data_4: return 2;
case FK_Data_8: return 3;
}
}
void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
// See <reloc.h>.
uint32_t FixupOffset =
Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
uint32_t FixupAddress =
Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
int64_t Value = 0;
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
Value = Target.getConstant();
if (IsPCRel) {
// Compensate for the relocation offset, Darwin x86_64 relocations only have
// the addend and appear to have attempted to define it to be the actual
// expression addend without the PCrel bias. However, instructions with data
// following the relocation are not accommodated for (see comment below
// regarding SIGNED{1,2,4}), so it isn't exactly that either.
Value += 1LL << Log2Size;
}
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
Type = macho::RIT_X86_64_Unsigned;
Index = 0;
// FIXME: I believe this is broken, I don't think the linker can understand
// it. I think it would require a local relocation, but I'm not sure if that
// would work either. The official way to get an absolute PCrel relocation
// is to use an absolute symbol (which we don't support yet).
if (IsPCRel) {
IsExtern = 1;
Type = macho::RIT_X86_64_Branch;
}
} else if (Target.getSymB()) { // A - B + constant
const MCSymbol *A = &Target.getSymA()->getSymbol();
MCSymbolData &A_SD = Asm.getSymbolData(*A);
const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
const MCSymbol *B = &Target.getSymB()->getSymbol();
MCSymbolData &B_SD = Asm.getSymbolData(*B);
const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
// Neither symbol can be modified.
if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported relocation of modified symbol");
// We don't support PCrel relocations of differences. Darwin 'as' doesn't
// implement most of these correctly.
if (IsPCRel)
report_fatal_error("unsupported pc-relative relocation of difference");
// The support for the situation where one or both of the symbols would
// require a local relocation is handled just like if the symbols were
// external. This is certainly used in the case of debug sections where the
// section has only temporary symbols and thus the symbols don't have base
// symbols. This is encoded using the section ordinal and non-extern
// relocation entries.
// Darwin 'as' doesn't emit correct relocations for this (it ends up with a
// single SIGNED relocation); reject it for now. Except the case where both
// symbols don't have a base, equal but both NULL.
if (A_Base == B_Base && A_Base)
report_fatal_error("unsupported relocation with identical base");
Value += Writer->getSymbolAddress(&A_SD, Layout) -
(A_Base == NULL ? 0 : Writer->getSymbolAddress(A_Base, Layout));
Value -= Writer->getSymbolAddress(&B_SD, Layout) -
(B_Base == NULL ? 0 : Writer->getSymbolAddress(B_Base, Layout));
if (A_Base) {
Index = A_Base->getIndex();
IsExtern = 1;
}
else {
Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = macho::RIT_X86_64_Unsigned;
macho::RelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
if (B_Base) {
Index = B_Base->getIndex();
IsExtern = 1;
}
else {
Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = macho::RIT_X86_64_Subtractor;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
const MCSymbolData *Base = Asm.getAtom(&SD);
// Relocations inside debug sections always use local relocations when
// possible. This seems to be done because the debugger doesn't fully
// understand x86_64 relocation entries, and expects to find values that
// have already been fixed up.
if (Symbol->isInSection()) {
const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
Fragment->getParent()->getSection());
if (Section.hasAttribute(MCSectionMachO::S_ATTR_DEBUG))
Base = 0;
}
// x86_64 almost always uses external relocations, except when there is no
// symbol to use as a base address (a local symbol with no preceding
// non-local symbol).
if (Base) {
Index = Base->getIndex();
IsExtern = 1;
// Add the local offset, if needed.
if (Base != &SD)
Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
} else if (Symbol->isInSection() && !Symbol->isVariable()) {
// The index is the section ordinal (1-based).
Index = SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
Value += Writer->getSymbolAddress(&SD, Layout);
if (IsPCRel)
Value -= FixupAddress + (1 << Log2Size);
} else if (Symbol->isVariable()) {
const MCExpr *Value = Symbol->getVariableValue();
int64_t Res;
bool isAbs = Value->EvaluateAsAbsolute(Res, Layout,
Writer->getSectionAddressMap());
if (isAbs) {
FixedValue = Res;
return;
} else {
report_fatal_error("unsupported relocation of variable '" +
Symbol->getName() + "'");
}
} else {
report_fatal_error("unsupported relocation of undefined symbol '" +
Symbol->getName() + "'");
}
MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
if (IsPCRel) {
if (IsRIPRel) {
if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
// x86_64 distinguishes movq foo@GOTPCREL so that the linker can
// rewrite the movq to an leaq at link time if the symbol ends up in
// the same linkage unit.
if (unsigned(Fixup.getKind()) == X86::reloc_riprel_4byte_movq_load)
Type = macho::RIT_X86_64_GOTLoad;
else
Type = macho::RIT_X86_64_GOT;
} else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
Type = macho::RIT_X86_64_TLV;
} else if (Modifier != MCSymbolRefExpr::VK_None) {
report_fatal_error("unsupported symbol modifier in relocation");
} else {
Type = macho::RIT_X86_64_Signed;
// The Darwin x86_64 relocation format has a problem where it cannot
// encode an address (L<foo> + <constant>) which is outside the atom
// containing L<foo>. Generally, this shouldn't occur but it does
// happen when we have a RIPrel instruction with data following the
// relocation entry (e.g., movb $012, L0(%rip)). Even with the PCrel
// adjustment Darwin x86_64 uses, the offset is still negative and the
// linker has no way to recognize this.
//
// To work around this, Darwin uses several special relocation types
// to indicate the offsets. However, the specification or
// implementation of these seems to also be incomplete; they should
// adjust the addend as well based on the actual encoded instruction
// (the additional bias), but instead appear to just look at the final
// offset.
switch (-(Target.getConstant() + (1LL << Log2Size))) {
case 1: Type = macho::RIT_X86_64_Signed1; break;
case 2: Type = macho::RIT_X86_64_Signed2; break;
case 4: Type = macho::RIT_X86_64_Signed4; break;
}
}
} else {
if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in branch "
"relocation");
Type = macho::RIT_X86_64_Branch;
}
} else {
if (Modifier == MCSymbolRefExpr::VK_GOT) {
Type = macho::RIT_X86_64_GOT;
} else if (Modifier == MCSymbolRefExpr::VK_GOTPCREL) {
// GOTPCREL is allowed as a modifier on non-PCrel instructions, in which
// case all we do is set the PCrel bit in the relocation entry; this is
// used with exception handling, for example. The source is required to
// include any necessary offset directly.
Type = macho::RIT_X86_64_GOT;
IsPCRel = 1;
} else if (Modifier == MCSymbolRefExpr::VK_TLVP) {
report_fatal_error("TLVP symbol modifier should have been rip-rel");
} else if (Modifier != MCSymbolRefExpr::VK_None)
report_fatal_error("unsupported symbol modifier in relocation");
else
Type = macho::RIT_X86_64_Unsigned;
}
}
// x86_64 always writes custom values into the fixups.
FixedValue = Value;
// struct relocation_info (8 bytes)
macho::RelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
}
void X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
unsigned Log2Size,
uint64_t &FixedValue) {
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned Type = macho::RIT_Vanilla;
// See <reloc.h>.
const MCSymbol *A = &Target.getSymA()->getSymbol();
MCSymbolData *A_SD = &Asm.getSymbolData(*A);
if (!A_SD->getFragment())
report_fatal_error("symbol '" + A->getName() +
"' can not be undefined in a subtraction expression");
uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
uint64_t SecAddr = Writer->getSectionAddress(A_SD->getFragment()->getParent());
FixedValue += SecAddr;
uint32_t Value2 = 0;
if (const MCSymbolRefExpr *B = Target.getSymB()) {
MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
if (!B_SD->getFragment())
report_fatal_error("symbol '" + B->getSymbol().getName() +
"' can not be undefined in a subtraction expression");
// Select the appropriate difference relocation type.
//
// Note that there is no longer any semantic difference between these two
// relocation types from the linkers point of view, this is done solely for
// pedantic compatibility with 'as'.
Type = A_SD->isExternal() ? (unsigned)macho::RIT_Difference :
(unsigned)macho::RIT_Generic_LocalDifference;
Value2 = Writer->getSymbolAddress(B_SD, Layout);
FixedValue -= Writer->getSectionAddress(B_SD->getFragment()->getParent());
}
// Relocations are written out in reverse order, so the PAIR comes first.
if (Type == macho::RIT_Difference ||
Type == macho::RIT_Generic_LocalDifference) {
macho::RelocationEntry MRE;
MRE.Word0 = ((0 << 0) |
(macho::RIT_Pair << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
macho::RF_Scattered);
MRE.Word1 = Value2;
Writer->addRelocation(Fragment->getParent(), MRE);
}
macho::RelocationEntry MRE;
MRE.Word0 = ((FixupOffset << 0) |
(Type << 24) |
(Log2Size << 28) |
(IsPCRel << 30) |
macho::RF_Scattered);
MRE.Word1 = Value;
Writer->addRelocation(Fragment->getParent(), MRE);
}
void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
assert(Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP &&
!is64Bit() &&
"Should only be called with a 32-bit TLVP relocation!");
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
uint32_t Value = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned IsPCRel = 0;
// Get the symbol data.
MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
unsigned Index = SD_A->getIndex();
// We're only going to have a second symbol in pic mode and it'll be a
// subtraction from the picbase. For 32-bit pic the addend is the difference
// between the picbase and the next address. For 32-bit static the addend is
// zero.
if (Target.getSymB()) {
// If this is a subtraction then we're pcrel.
uint32_t FixupAddress =
Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset();
MCSymbolData *SD_B = &Asm.getSymbolData(Target.getSymB()->getSymbol());
IsPCRel = 1;
FixedValue = (FixupAddress - Writer->getSymbolAddress(SD_B, Layout) +
Target.getConstant());
FixedValue += 1ULL << Log2Size;
} else {
FixedValue = 0;
}
// struct relocation_info (8 bytes)
macho::RelocationEntry MRE;
MRE.Word0 = Value;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(1 << 27) | // Extern
(macho::RIT_Generic_TLV << 28)); // Type
Writer->addRelocation(Fragment->getParent(), MRE);
}
void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
// If this is a 32-bit TLVP reloc it's handled a bit differently.
if (Target.getSymA() &&
Target.getSymA()->getKind() == MCSymbolRefExpr::VK_TLVP) {
RecordTLVPRelocation(Writer, Asm, Layout, Fragment, Fixup, Target,
FixedValue);
return;
}
// If this is a difference or a defined symbol plus an offset, then we need a
// scattered relocation entry. Differences always require scattered
// relocations.
if (Target.getSymB())
return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
Target, Log2Size, FixedValue);
// Get the symbol data, if any.
MCSymbolData *SD = 0;
if (Target.getSymA())
SD = &Asm.getSymbolData(Target.getSymA()->getSymbol());
// If this is an internal relocation with an offset, it also needs a scattered
// relocation entry.
uint32_t Offset = Target.getConstant();
if (IsPCRel)
Offset += 1 << Log2Size;
if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
Target, Log2Size, FixedValue);
// See <reloc.h>.
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
//
// FIXME: Currently, these are never generated (see code below). I cannot
// find a case where they are actually emitted.
Type = macho::RIT_Vanilla;
} else {
// Resolve constant variables.
if (SD->getSymbol().isVariable()) {
int64_t Res;
if (SD->getSymbol().getVariableValue()->EvaluateAsAbsolute(
Res, Layout, Writer->getSectionAddressMap())) {
FixedValue = Res;
return;
}
}
// Check whether we need an external or internal relocation.
if (Writer->doesSymbolRequireExternRelocation(SD)) {
IsExtern = 1;
Index = SD->getIndex();
// For external relocations, make sure to offset the fixup value to
// compensate for the addend of the symbol address, if it was
// undefined. This occurs with weak definitions, for example.
if (!SD->Symbol->isUndefined())
FixedValue -= Layout.getSymbolOffset(SD);
} else {
// The index is the section ordinal (1-based).
const MCSectionData &SymSD = Asm.getSectionData(
SD->getSymbol().getSection());
Index = SymSD.getOrdinal() + 1;
FixedValue += Writer->getSectionAddress(&SymSD);
}
if (IsPCRel)
FixedValue -= Writer->getSectionAddress(Fragment->getParent());
Type = macho::RIT_Vanilla;
}
// struct relocation_info (8 bytes)
macho::RelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
}
MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,
bool Is64Bit,
uint32_t CPUType,
uint32_t CPUSubtype) {
return createMachObjectWriter(new X86MachObjectWriter(Is64Bit,
CPUType,
CPUSubtype),
OS, /*IsLittleEndian=*/true);
}
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