//===-- ARMMachObjectWriter.cpp - ARM Mach Object Writer ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/ARMMCTargetDesc.h"
#include "MCTargetDesc/ARMBaseInfo.h"
#include "MCTargetDesc/ARMFixupKinds.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCMachOSymbolFlags.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Object/MachOFormat.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;
using namespace llvm::object;
namespace {
class ARMMachObjectWriter : public MCMachObjectTargetWriter {
void RecordARMScatteredRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
unsigned Log2Size,
uint64_t &FixedValue);
void RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
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)
: MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
/*UseAggressiveSymbolFolding=*/true) {}
void RecordRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue);
};
}
static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
unsigned &Log2Size) {
RelocType = unsigned(macho::RIT_Vanilla);
Log2Size = ~0U;
switch (Kind) {
default:
return false;
case FK_Data_1:
Log2Size = llvm::Log2_32(1);
return true;
case FK_Data_2:
Log2Size = llvm::Log2_32(2);
return true;
case FK_Data_4:
Log2Size = llvm::Log2_32(4);
return true;
case FK_Data_8:
Log2Size = llvm::Log2_32(8);
return true;
// Handle 24-bit branch kinds.
case ARM::fixup_arm_ldst_pcrel_12:
case ARM::fixup_arm_pcrel_10:
case ARM::fixup_arm_adr_pcrel_12:
case ARM::fixup_arm_condbranch:
case ARM::fixup_arm_uncondbranch:
case ARM::fixup_arm_uncondbl:
case ARM::fixup_arm_condbl:
case ARM::fixup_arm_blx:
RelocType = unsigned(macho::RIT_ARM_Branch24Bit);
// Report as 'long', even though that is not quite accurate.
Log2Size = llvm::Log2_32(4);
return true;
// Handle Thumb branches.
case ARM::fixup_arm_thumb_br:
RelocType = unsigned(macho::RIT_ARM_ThumbBranch22Bit);
Log2Size = llvm::Log2_32(2);
return true;
case ARM::fixup_t2_uncondbranch:
case ARM::fixup_arm_thumb_bl:
case ARM::fixup_arm_thumb_blx:
RelocType = unsigned(macho::RIT_ARM_ThumbBranch22Bit);
Log2Size = llvm::Log2_32(4);
return true;
// For movw/movt r_type relocations they always have a pair following them and
// the r_length bits are used differently. The encoding of the r_length is as
// follows:
// low bit of r_length:
// 0 - :lower16: for movw instructions
// 1 - :upper16: for movt instructions
// high bit of r_length:
// 0 - arm instructions
// 1 - thumb instructions
case ARM::fixup_arm_movt_hi16:
case ARM::fixup_arm_movt_hi16_pcrel:
RelocType = unsigned(macho::RIT_ARM_Half);
Log2Size = 1;
return true;
case ARM::fixup_t2_movt_hi16:
case ARM::fixup_t2_movt_hi16_pcrel:
RelocType = unsigned(macho::RIT_ARM_Half);
Log2Size = 3;
return true;
case ARM::fixup_arm_movw_lo16:
case ARM::fixup_arm_movw_lo16_pcrel:
RelocType = unsigned(macho::RIT_ARM_Half);
Log2Size = 0;
return true;
case ARM::fixup_t2_movw_lo16:
case ARM::fixup_t2_movw_lo16_pcrel:
RelocType = unsigned(macho::RIT_ARM_Half);
Log2Size = 2;
return true;
}
}
void ARMMachObjectWriter::
RecordARMScatteredHalfRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned Type = macho::RIT_ARM_Half;
// See <reloc.h>.
const MCSymbol *A = &Target.getSymA()->getSymbol();
MCSymbolData *A_SD = &Asm.getSymbolData(*A);
if (!A_SD->getFragment())
Asm.getContext().FatalError(Fixup.getLoc(),
"symbol '" + A->getName() +
"' can not be undefined in a subtraction expression");
uint32_t Value = Writer->getSymbolAddress(A_SD, Layout);
uint32_t Value2 = 0;
uint64_t SecAddr =
Writer->getSectionAddress(A_SD->getFragment()->getParent());
FixedValue += SecAddr;
if (const MCSymbolRefExpr *B = Target.getSymB()) {
MCSymbolData *B_SD = &Asm.getSymbolData(B->getSymbol());
if (!B_SD->getFragment())
Asm.getContext().FatalError(Fixup.getLoc(),
"symbol '" + B->getSymbol().getName() +
"' can not be undefined in a subtraction expression");
// Select the appropriate difference relocation type.
Type = macho::RIT_ARM_HalfDifference;
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.
// ARM_RELOC_HALF and ARM_RELOC_HALF_SECTDIFF abuse the r_length field:
//
// For these two r_type relocations they always have a pair following them and
// the r_length bits are used differently. The encoding of the r_length is as
// follows:
// low bit of r_length:
// 0 - :lower16: for movw instructions
// 1 - :upper16: for movt instructions
// high bit of r_length:
// 0 - arm instructions
// 1 - thumb instructions
// the other half of the relocated expression is in the following pair
// relocation entry in the low 16 bits of r_address field.
unsigned ThumbBit = 0;
unsigned MovtBit = 0;
switch ((unsigned)Fixup.getKind()) {
default: break;
case ARM::fixup_arm_movt_hi16:
case ARM::fixup_arm_movt_hi16_pcrel:
MovtBit = 1;
// The thumb bit shouldn't be set in the 'other-half' bit of the
// relocation, but it will be set in FixedValue if the base symbol
// is a thumb function. Clear it out here.
if (A_SD->getFlags() & SF_ThumbFunc)
FixedValue &= 0xfffffffe;
break;
case ARM::fixup_t2_movt_hi16:
case ARM::fixup_t2_movt_hi16_pcrel:
if (A_SD->getFlags() & SF_ThumbFunc)
FixedValue &= 0xfffffffe;
MovtBit = 1;
// Fallthrough
case ARM::fixup_t2_movw_lo16:
case ARM::fixup_t2_movw_lo16_pcrel:
ThumbBit = 1;
break;
}
if (Type == macho::RIT_ARM_HalfDifference) {
uint32_t OtherHalf = MovtBit
? (FixedValue & 0xffff) : ((FixedValue & 0xffff0000) >> 16);
macho::RelocationEntry MRE;
MRE.Word0 = ((OtherHalf << 0) |
(macho::RIT_Pair << 24) |
(MovtBit << 28) |
(ThumbBit << 29) |
(IsPCRel << 30) |
macho::RF_Scattered);
MRE.Word1 = Value2;
Writer->addRelocation(Fragment->getParent(), MRE);
}
macho::RelocationEntry MRE;
MRE.Word0 = ((FixupOffset << 0) |
(Type << 24) |
(MovtBit << 28) |
(ThumbBit << 29) |
(IsPCRel << 30) |
macho::RF_Scattered);
MRE.Word1 = Value;
Writer->addRelocation(Fragment->getParent(), MRE);
}
void ARMMachObjectWriter::RecordARMScatteredRelocation(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())
Asm.getContext().FatalError(Fixup.getLoc(),
"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())
Asm.getContext().FatalError(Fixup.getLoc(),
"symbol '" + B->getSymbol().getName() +
"' can not be undefined in a subtraction expression");
// Select the appropriate difference relocation type.
Type = macho::RIT_Difference;
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);
}
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,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned Log2Size;
unsigned RelocType = macho::RIT_Vanilla;
if (!getARMFixupKindMachOInfo(Fixup.getKind(), RelocType, Log2Size))
// If we failed to get fixup kind info, it's because there's no legal
// relocation type for the fixup kind. This happens when it's a fixup that's
// expected to always be resolvable at assembly time and not have any
// relocations needed.
Asm.getContext().FatalError(Fixup.getLoc(),
"unsupported relocation on symbol");
// 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()) {
if (RelocType == macho::RIT_ARM_Half)
return RecordARMScatteredHalfRelocation(Writer, Asm, Layout, Fragment,
Fixup, Target, FixedValue);
return RecordARMScatteredRelocation(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());
// FIXME: For other platforms, we need to use scattered relocations for
// internal relocations with offsets. If this is an internal relocation with
// an offset, it also needs a scattered relocation entry.
//
// Is this right for ARM?
uint32_t Offset = Target.getConstant();
if (IsPCRel && RelocType == macho::RIT_Vanilla)
Offset += 1 << Log2Size;
if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
return RecordARMScatteredRelocation(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
// FIXME!
report_fatal_error("FIXME: relocations to absolute targets "
"not yet implemented");
} 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 (requiresExternRelocation(Writer, Asm, *Fragment, RelocType, SD,
FixedValue)) {
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());
// The type is determined by the fixup kind.
Type = RelocType;
}
// struct relocation_info (8 bytes)
macho::RelocationEntry MRE;
MRE.Word0 = FixupOffset;
MRE.Word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
// Even when it's not a scattered relocation, movw/movt always uses
// a PAIR relocation.
if (Type == macho::RIT_ARM_Half) {
// The other-half value only gets populated for the movt and movw
// relocation entries.
uint32_t Value = 0;
switch ((unsigned)Fixup.getKind()) {
default: break;
case ARM::fixup_arm_movw_lo16:
case ARM::fixup_arm_movw_lo16_pcrel:
case ARM::fixup_t2_movw_lo16:
case ARM::fixup_t2_movw_lo16_pcrel:
Value = (FixedValue >> 16) & 0xffff;
break;
case ARM::fixup_arm_movt_hi16:
case ARM::fixup_arm_movt_hi16_pcrel:
case ARM::fixup_t2_movt_hi16:
case ARM::fixup_t2_movt_hi16_pcrel:
Value = FixedValue & 0xffff;
break;
}
macho::RelocationEntry MREPair;
MREPair.Word0 = Value;
MREPair.Word1 = ((0xffffff) |
(Log2Size << 25) |
(macho::RIT_Pair << 28));
Writer->addRelocation(Fragment->getParent(), MREPair);
}
Writer->addRelocation(Fragment->getParent(), MRE);
}
MCObjectWriter *llvm::createARMMachObjectWriter(raw_ostream &OS,
bool Is64Bit,
uint32_t CPUType,
uint32_t CPUSubtype) {
return createMachObjectWriter(new ARMMachObjectWriter(Is64Bit,
CPUType,
CPUSubtype),
OS, /*IsLittleEndian=*/true);
}