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llvm-project/lld/ELF/Arch/ARM.cpp

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//===- ARM.cpp ------------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Error.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Thunks.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::support::endian;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf;
namespace {
class ARM final : public TargetInfo {
public:
ARM();
RelExpr getRelExpr(uint32_t Type, const SymbolBody &S,
const uint8_t *Loc) const override;
bool isPicRel(uint32_t Type) const override;
uint32_t getDynRel(uint32_t Type) const override;
int64_t getImplicitAddend(const uint8_t *Buf, uint32_t Type) const override;
void writeGotPlt(uint8_t *Buf, const SymbolBody &S) const override;
void writeIgotPlt(uint8_t *Buf, const SymbolBody &S) const override;
void writePltHeader(uint8_t *Buf) const override;
void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr,
int32_t Index, unsigned RelOff) const override;
void addPltSymbols(InputSectionBase *IS, uint64_t Off) const override;
void addPltHeaderSymbols(InputSectionBase *ISD) const override;
bool needsThunk(RelExpr Expr, uint32_t RelocType, const InputFile *File,
const SymbolBody &S) const override;
void relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const override;
};
} // namespace
ARM::ARM() {
CopyRel = R_ARM_COPY;
RelativeRel = R_ARM_RELATIVE;
IRelativeRel = R_ARM_IRELATIVE;
GotRel = R_ARM_GLOB_DAT;
PltRel = R_ARM_JUMP_SLOT;
TlsGotRel = R_ARM_TLS_TPOFF32;
TlsModuleIndexRel = R_ARM_TLS_DTPMOD32;
TlsOffsetRel = R_ARM_TLS_DTPOFF32;
GotEntrySize = 4;
GotPltEntrySize = 4;
PltEntrySize = 16;
PltHeaderSize = 20;
TrapInstr = 0xd4d4d4d4;
// ARM uses Variant 1 TLS
TcbSize = 8;
NeedsThunks = true;
}
RelExpr ARM::getRelExpr(uint32_t Type, const SymbolBody &S,
const uint8_t *Loc) const {
switch (Type) {
default:
return R_ABS;
case R_ARM_THM_JUMP11:
return R_PC;
case R_ARM_CALL:
case R_ARM_JUMP24:
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_PREL31:
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
case R_ARM_THM_CALL:
return R_PLT_PC;
case R_ARM_GOTOFF32:
// (S + A) - GOT_ORG
return R_GOTREL;
case R_ARM_GOT_BREL:
// GOT(S) + A - GOT_ORG
return R_GOT_OFF;
case R_ARM_GOT_PREL:
case R_ARM_TLS_IE32:
// GOT(S) + A - P
return R_GOT_PC;
case R_ARM_SBREL32:
return R_ARM_SBREL;
case R_ARM_TARGET1:
return Config->Target1Rel ? R_PC : R_ABS;
case R_ARM_TARGET2:
if (Config->Target2 == Target2Policy::Rel)
return R_PC;
if (Config->Target2 == Target2Policy::Abs)
return R_ABS;
return R_GOT_PC;
case R_ARM_TLS_GD32:
return R_TLSGD_PC;
case R_ARM_TLS_LDM32:
return R_TLSLD_PC;
case R_ARM_BASE_PREL:
// B(S) + A - P
// FIXME: currently B(S) assumed to be .got, this may not hold for all
// platforms.
return R_GOTONLY_PC;
case R_ARM_MOVW_PREL_NC:
case R_ARM_MOVT_PREL:
case R_ARM_REL32:
case R_ARM_THM_MOVW_PREL_NC:
case R_ARM_THM_MOVT_PREL:
return R_PC;
case R_ARM_NONE:
return R_NONE;
case R_ARM_TLS_LE32:
return R_TLS;
}
}
bool ARM::isPicRel(uint32_t Type) const {
return (Type == R_ARM_TARGET1 && !Config->Target1Rel) ||
(Type == R_ARM_ABS32);
}
uint32_t ARM::getDynRel(uint32_t Type) const {
if (Type == R_ARM_TARGET1 && !Config->Target1Rel)
return R_ARM_ABS32;
if (Type == R_ARM_ABS32)
return Type;
// Keep it going with a dummy value so that we can find more reloc errors.
return R_ARM_ABS32;
}
void ARM::writeGotPlt(uint8_t *Buf, const SymbolBody &) const {
write32le(Buf, InX::Plt->getVA());
}
void ARM::writeIgotPlt(uint8_t *Buf, const SymbolBody &S) const {
// An ARM entry is the address of the ifunc resolver function.
write32le(Buf, S.getVA());
}
void ARM::writePltHeader(uint8_t *Buf) const {
const uint8_t PltData[] = {
0x04, 0xe0, 0x2d, 0xe5, // str lr, [sp,#-4]!
0x04, 0xe0, 0x9f, 0xe5, // ldr lr, L2
0x0e, 0xe0, 0x8f, 0xe0, // L1: add lr, pc, lr
0x08, 0xf0, 0xbe, 0xe5, // ldr pc, [lr, #8]
0x00, 0x00, 0x00, 0x00, // L2: .word &(.got.plt) - L1 - 8
};
memcpy(Buf, PltData, sizeof(PltData));
uint64_t GotPlt = InX::GotPlt->getVA();
uint64_t L1 = InX::Plt->getVA() + 8;
write32le(Buf + 16, GotPlt - L1 - 8);
}
void ARM::addPltHeaderSymbols(InputSectionBase *ISD) const {
auto *IS = cast<InputSection>(ISD);
addSyntheticLocal("$a", STT_NOTYPE, 0, 0, IS);
addSyntheticLocal("$d", STT_NOTYPE, 16, 0, IS);
}
void ARM::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
uint64_t PltEntryAddr, int32_t Index,
unsigned RelOff) const {
// FIXME: Using simple code sequence with simple relocations.
// There is a more optimal sequence but it requires support for the group
// relocations. See ELF for the ARM Architecture Appendix A.3
const uint8_t PltData[] = {
0x04, 0xc0, 0x9f, 0xe5, // ldr ip, L2
0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
0x00, 0xf0, 0x9c, 0xe5, // ldr pc, [ip]
0x00, 0x00, 0x00, 0x00, // L2: .word Offset(&(.plt.got) - L1 - 8
};
memcpy(Buf, PltData, sizeof(PltData));
uint64_t L1 = PltEntryAddr + 4;
write32le(Buf + 12, GotPltEntryAddr - L1 - 8);
}
void ARM::addPltSymbols(InputSectionBase *ISD, uint64_t Off) const {
auto *IS = cast<InputSection>(ISD);
addSyntheticLocal("$a", STT_NOTYPE, Off, 0, IS);
addSyntheticLocal("$d", STT_NOTYPE, Off + 12, 0, IS);
}
bool ARM::needsThunk(RelExpr Expr, uint32_t RelocType, const InputFile *File,
const SymbolBody &S) const {
// If S is an undefined weak symbol in an executable we don't need a Thunk.
// In a DSO calls to undefined symbols, including weak ones get PLT entries
// which may need a thunk.
if (S.isUndefined() && !S.isLocal() && S.symbol()->isWeak() &&
!Config->Shared)
return false;
// A state change from ARM to Thumb and vice versa must go through an
// interworking thunk if the relocation type is not R_ARM_CALL or
// R_ARM_THM_CALL.
switch (RelocType) {
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_JUMP24:
// Source is ARM, all PLT entries are ARM so no interworking required.
// Otherwise we need to interwork if Symbol has bit 0 set (Thumb).
if (Expr == R_PC && ((S.getVA() & 1) == 1))
return true;
break;
case R_ARM_THM_JUMP19:
case R_ARM_THM_JUMP24:
// Source is Thumb, all PLT entries are ARM so interworking is required.
// Otherwise we need to interwork if Symbol has bit 0 clear (ARM).
if (Expr == R_PLT_PC || ((S.getVA() & 1) == 0))
return true;
break;
}
return false;
}
void ARM::relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const {
switch (Type) {
case R_ARM_ABS32:
case R_ARM_BASE_PREL:
case R_ARM_GLOB_DAT:
case R_ARM_GOTOFF32:
case R_ARM_GOT_BREL:
case R_ARM_GOT_PREL:
case R_ARM_REL32:
case R_ARM_RELATIVE:
case R_ARM_SBREL32:
case R_ARM_TARGET1:
case R_ARM_TARGET2:
case R_ARM_TLS_GD32:
case R_ARM_TLS_IE32:
case R_ARM_TLS_LDM32:
case R_ARM_TLS_LDO32:
case R_ARM_TLS_LE32:
case R_ARM_TLS_TPOFF32:
case R_ARM_TLS_DTPOFF32:
write32le(Loc, Val);
break;
case R_ARM_TLS_DTPMOD32:
write32le(Loc, 1);
break;
case R_ARM_PREL31:
checkInt<31>(Loc, Val, Type);
write32le(Loc, (read32le(Loc) & 0x80000000) | (Val & ~0x80000000));
break;
case R_ARM_CALL:
// R_ARM_CALL is used for BL and BLX instructions, depending on the
// value of bit 0 of Val, we must select a BL or BLX instruction
if (Val & 1) {
// If bit 0 of Val is 1 the target is Thumb, we must select a BLX.
// The BLX encoding is 0xfa:H:imm24 where Val = imm24:H:'1'
checkInt<26>(Loc, Val, Type);
write32le(Loc, 0xfa000000 | // opcode
((Val & 2) << 23) | // H
((Val >> 2) & 0x00ffffff)); // imm24
break;
}
if ((read32le(Loc) & 0xfe000000) == 0xfa000000)
// BLX (always unconditional) instruction to an ARM Target, select an
// unconditional BL.
write32le(Loc, 0xeb000000 | (read32le(Loc) & 0x00ffffff));
// fall through as BL encoding is shared with B
LLVM_FALLTHROUGH;
case R_ARM_JUMP24:
case R_ARM_PC24:
case R_ARM_PLT32:
checkInt<26>(Loc, Val, Type);
write32le(Loc, (read32le(Loc) & ~0x00ffffff) | ((Val >> 2) & 0x00ffffff));
break;
case R_ARM_THM_JUMP11:
checkInt<12>(Loc, Val, Type);
write16le(Loc, (read32le(Loc) & 0xf800) | ((Val >> 1) & 0x07ff));
break;
case R_ARM_THM_JUMP19:
// Encoding T3: Val = S:J2:J1:imm6:imm11:0
checkInt<21>(Loc, Val, Type);
write16le(Loc,
(read16le(Loc) & 0xfbc0) | // opcode cond
((Val >> 10) & 0x0400) | // S
((Val >> 12) & 0x003f)); // imm6
write16le(Loc + 2,
0x8000 | // opcode
((Val >> 8) & 0x0800) | // J2
((Val >> 5) & 0x2000) | // J1
((Val >> 1) & 0x07ff)); // imm11
break;
case R_ARM_THM_CALL:
// R_ARM_THM_CALL is used for BL and BLX instructions, depending on the
// value of bit 0 of Val, we must select a BL or BLX instruction
if ((Val & 1) == 0) {
// Ensure BLX destination is 4-byte aligned. As BLX instruction may
// only be two byte aligned. This must be done before overflow check
Val = alignTo(Val, 4);
}
// Bit 12 is 0 for BLX, 1 for BL
write16le(Loc + 2, (read16le(Loc + 2) & ~0x1000) | (Val & 1) << 12);
// Fall through as rest of encoding is the same as B.W
LLVM_FALLTHROUGH;
case R_ARM_THM_JUMP24:
// Encoding B T4, BL T1, BLX T2: Val = S:I1:I2:imm10:imm11:0
// FIXME: Use of I1 and I2 require v6T2ops
checkInt<25>(Loc, Val, Type);
write16le(Loc,
0xf000 | // opcode
((Val >> 14) & 0x0400) | // S
((Val >> 12) & 0x03ff)); // imm10
write16le(Loc + 2,
(read16le(Loc + 2) & 0xd000) | // opcode
(((~(Val >> 10)) ^ (Val >> 11)) & 0x2000) | // J1
(((~(Val >> 11)) ^ (Val >> 13)) & 0x0800) | // J2
((Val >> 1) & 0x07ff)); // imm11
break;
case R_ARM_MOVW_ABS_NC:
case R_ARM_MOVW_PREL_NC:
write32le(Loc, (read32le(Loc) & ~0x000f0fff) | ((Val & 0xf000) << 4) |
(Val & 0x0fff));
break;
case R_ARM_MOVT_ABS:
case R_ARM_MOVT_PREL:
checkInt<32>(Loc, Val, Type);
write32le(Loc, (read32le(Loc) & ~0x000f0fff) |
(((Val >> 16) & 0xf000) << 4) | ((Val >> 16) & 0xfff));
break;
case R_ARM_THM_MOVT_ABS:
case R_ARM_THM_MOVT_PREL:
// Encoding T1: A = imm4:i:imm3:imm8
checkInt<32>(Loc, Val, Type);
write16le(Loc,
0xf2c0 | // opcode
((Val >> 17) & 0x0400) | // i
((Val >> 28) & 0x000f)); // imm4
write16le(Loc + 2,
(read16le(Loc + 2) & 0x8f00) | // opcode
((Val >> 12) & 0x7000) | // imm3
((Val >> 16) & 0x00ff)); // imm8
break;
case R_ARM_THM_MOVW_ABS_NC:
case R_ARM_THM_MOVW_PREL_NC:
// Encoding T3: A = imm4:i:imm3:imm8
write16le(Loc,
0xf240 | // opcode
((Val >> 1) & 0x0400) | // i
((Val >> 12) & 0x000f)); // imm4
write16le(Loc + 2,
(read16le(Loc + 2) & 0x8f00) | // opcode
((Val << 4) & 0x7000) | // imm3
(Val & 0x00ff)); // imm8
break;
default:
error(getErrorLocation(Loc) + "unrecognized reloc " + Twine(Type));
}
}
int64_t ARM::getImplicitAddend(const uint8_t *Buf, uint32_t Type) const {
switch (Type) {
default:
return 0;
case R_ARM_ABS32:
case R_ARM_BASE_PREL:
case R_ARM_GOTOFF32:
case R_ARM_GOT_BREL:
case R_ARM_GOT_PREL:
case R_ARM_REL32:
case R_ARM_TARGET1:
case R_ARM_TARGET2:
case R_ARM_TLS_GD32:
case R_ARM_TLS_LDM32:
case R_ARM_TLS_LDO32:
case R_ARM_TLS_IE32:
case R_ARM_TLS_LE32:
return SignExtend64<32>(read32le(Buf));
case R_ARM_PREL31:
return SignExtend64<31>(read32le(Buf));
case R_ARM_CALL:
case R_ARM_JUMP24:
case R_ARM_PC24:
case R_ARM_PLT32:
return SignExtend64<26>(read32le(Buf) << 2);
case R_ARM_THM_JUMP11:
return SignExtend64<12>(read16le(Buf) << 1);
case R_ARM_THM_JUMP19: {
// Encoding T3: A = S:J2:J1:imm10:imm6:0
uint16_t Hi = read16le(Buf);
uint16_t Lo = read16le(Buf + 2);
return SignExtend64<20>(((Hi & 0x0400) << 10) | // S
((Lo & 0x0800) << 8) | // J2
((Lo & 0x2000) << 5) | // J1
((Hi & 0x003f) << 12) | // imm6
((Lo & 0x07ff) << 1)); // imm11:0
}
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24: {
// Encoding B T4, BL T1, BLX T2: A = S:I1:I2:imm10:imm11:0
// I1 = NOT(J1 EOR S), I2 = NOT(J2 EOR S)
// FIXME: I1 and I2 require v6T2ops
uint16_t Hi = read16le(Buf);
uint16_t Lo = read16le(Buf + 2);
return SignExtend64<24>(((Hi & 0x0400) << 14) | // S
(~((Lo ^ (Hi << 3)) << 10) & 0x00800000) | // I1
(~((Lo ^ (Hi << 1)) << 11) & 0x00400000) | // I2
((Hi & 0x003ff) << 12) | // imm0
((Lo & 0x007ff) << 1)); // imm11:0
}
// ELF for the ARM Architecture 4.6.1.1 the implicit addend for MOVW and
// MOVT is in the range -32768 <= A < 32768
case R_ARM_MOVW_ABS_NC:
case R_ARM_MOVT_ABS:
case R_ARM_MOVW_PREL_NC:
case R_ARM_MOVT_PREL: {
uint64_t Val = read32le(Buf) & 0x000f0fff;
return SignExtend64<16>(((Val & 0x000f0000) >> 4) | (Val & 0x00fff));
}
case R_ARM_THM_MOVW_ABS_NC:
case R_ARM_THM_MOVT_ABS:
case R_ARM_THM_MOVW_PREL_NC:
case R_ARM_THM_MOVT_PREL: {
// Encoding T3: A = imm4:i:imm3:imm8
uint16_t Hi = read16le(Buf);
uint16_t Lo = read16le(Buf + 2);
return SignExtend64<16>(((Hi & 0x000f) << 12) | // imm4
((Hi & 0x0400) << 1) | // i
((Lo & 0x7000) >> 4) | // imm3
(Lo & 0x00ff)); // imm8
}
}
}
TargetInfo *elf::getARMTargetInfo() {
static ARM Target;
return &Target;
}
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