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

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//===- ARM.cpp ------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "InputFiles.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Thunks.h"
#include "lld/Common/ErrorHandler.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();
uint32_t calcEFlags() const override;
RelExpr getRelExpr(RelType type, const Symbol &s,
const uint8_t *loc) const override;
RelType getDynRel(RelType type) const override;
int64_t getImplicitAddend(const uint8_t *buf, RelType type) const override;
void writeGotPlt(uint8_t *buf, const Symbol &s) const override;
void writeIgotPlt(uint8_t *buf, const Symbol &s) const override;
void writePltHeader(uint8_t *buf) const override;
void writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const override;
void addPltSymbols(InputSection &isec, uint64_t off) const override;
void addPltHeaderSymbols(InputSection &isd) const override;
bool needsThunk(RelExpr expr, RelType type, const InputFile *file,
uint64_t branchAddr, const Symbol &s,
int64_t a) const override;
uint32_t getThunkSectionSpacing() const override;
bool inBranchRange(RelType type, uint64_t src, uint64_t dst) const override;
void relocate(uint8_t *loc, const Relocation &rel,
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;
symbolicRel = R_ARM_ABS32;
tlsGotRel = R_ARM_TLS_TPOFF32;
tlsModuleIndexRel = R_ARM_TLS_DTPMOD32;
tlsOffsetRel = R_ARM_TLS_DTPOFF32;
pltHeaderSize = 32;
pltEntrySize = 16;
ipltEntrySize = 16;
trapInstr = {0xd4, 0xd4, 0xd4, 0xd4};
needsThunks = true;
defaultMaxPageSize = 65536;
}
uint32_t ARM::calcEFlags() const {
// The ABIFloatType is used by loaders to detect the floating point calling
// convention.
uint32_t abiFloatType = 0;
if (config->armVFPArgs == ARMVFPArgKind::Base ||
config->armVFPArgs == ARMVFPArgKind::Default)
abiFloatType = EF_ARM_ABI_FLOAT_SOFT;
else if (config->armVFPArgs == ARMVFPArgKind::VFP)
abiFloatType = EF_ARM_ABI_FLOAT_HARD;
// We don't currently use any features incompatible with EF_ARM_EABI_VER5,
// but we don't have any firm guarantees of conformance. Linux AArch64
// kernels (as of 2016) require an EABI version to be set.
return EF_ARM_EABI_VER5 | abiFloatType;
}
RelExpr ARM::getRelExpr(RelType type, const Symbol &s,
const uint8_t *loc) const {
switch (type) {
case R_ARM_ABS32:
case R_ARM_MOVW_ABS_NC:
case R_ARM_MOVT_ABS:
case R_ARM_THM_MOVW_ABS_NC:
case R_ARM_THM_MOVT_ABS:
return R_ABS;
case R_ARM_THM_JUMP8:
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_TLS_LDO32:
return R_DTPREL;
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_ALU_PC_G0:
case R_ARM_ALU_PC_G0_NC:
case R_ARM_ALU_PC_G1:
case R_ARM_ALU_PC_G1_NC:
case R_ARM_ALU_PC_G2:
case R_ARM_LDR_PC_G0:
case R_ARM_LDR_PC_G1:
case R_ARM_LDR_PC_G2:
case R_ARM_LDRS_PC_G0:
case R_ARM_LDRS_PC_G1:
case R_ARM_LDRS_PC_G2:
case R_ARM_THM_ALU_PREL_11_0:
case R_ARM_THM_PC8:
case R_ARM_THM_PC12:
return R_ARM_PCA;
case R_ARM_MOVW_BREL_NC:
case R_ARM_MOVW_BREL:
case R_ARM_MOVT_BREL:
case R_ARM_THM_MOVW_BREL_NC:
case R_ARM_THM_MOVW_BREL:
case R_ARM_THM_MOVT_BREL:
return R_ARM_SBREL;
case R_ARM_NONE:
return R_NONE;
case R_ARM_TLS_LE32:
return R_TPREL;
case R_ARM_V4BX:
// V4BX is just a marker to indicate there's a "bx rN" instruction at the
// given address. It can be used to implement a special linker mode which
// rewrites ARMv4T inputs to ARMv4. Since we support only ARMv4 input and
// not ARMv4 output, we can just ignore it.
return R_NONE;
default:
error(getErrorLocation(loc) + "unknown relocation (" + Twine(type) +
") against symbol " + toString(s));
return R_NONE;
}
}
RelType ARM::getDynRel(RelType type) const {
if ((type == R_ARM_ABS32) || (type == R_ARM_TARGET1 && !config->target1Rel))
return R_ARM_ABS32;
return R_ARM_NONE;
}
void ARM::writeGotPlt(uint8_t *buf, const Symbol &) const {
write32le(buf, in.plt->getVA());
}
void ARM::writeIgotPlt(uint8_t *buf, const Symbol &s) const {
// An ARM entry is the address of the ifunc resolver function.
write32le(buf, s.getVA());
}
// Long form PLT Header that does not have any restrictions on the displacement
// of the .plt from the .plt.got.
static void writePltHeaderLong(uint8_t *buf) {
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
0xd4, 0xd4, 0xd4, 0xd4, // Pad to 32-byte boundary
0xd4, 0xd4, 0xd4, 0xd4, // Pad to 32-byte boundary
0xd4, 0xd4, 0xd4, 0xd4};
memcpy(buf, pltData, sizeof(pltData));
uint64_t gotPlt = in.gotPlt->getVA();
uint64_t l1 = in.plt->getVA() + 8;
write32le(buf + 16, gotPlt - l1 - 8);
}
// The default PLT header requires the .plt.got to be within 128 Mb of the
// .plt in the positive direction.
void ARM::writePltHeader(uint8_t *buf) const {
// Use a similar sequence to that in writePlt(), the difference is the calling
// conventions mean we use lr instead of ip. The PLT entry is responsible for
// saving lr on the stack, the dynamic loader is responsible for reloading
// it.
const uint32_t pltData[] = {
0xe52de004, // L1: str lr, [sp,#-4]!
0xe28fe600, // add lr, pc, #0x0NN00000 &(.got.plt - L1 - 4)
0xe28eea00, // add lr, lr, #0x000NN000 &(.got.plt - L1 - 4)
0xe5bef000, // ldr pc, [lr, #0x00000NNN] &(.got.plt -L1 - 4)
};
uint64_t offset = in.gotPlt->getVA() - in.plt->getVA() - 4;
if (!llvm::isUInt<27>(offset)) {
// We cannot encode the Offset, use the long form.
writePltHeaderLong(buf);
return;
}
write32le(buf + 0, pltData[0]);
write32le(buf + 4, pltData[1] | ((offset >> 20) & 0xff));
write32le(buf + 8, pltData[2] | ((offset >> 12) & 0xff));
write32le(buf + 12, pltData[3] | (offset & 0xfff));
memcpy(buf + 16, trapInstr.data(), 4); // Pad to 32-byte boundary
memcpy(buf + 20, trapInstr.data(), 4);
memcpy(buf + 24, trapInstr.data(), 4);
memcpy(buf + 28, trapInstr.data(), 4);
}
void ARM::addPltHeaderSymbols(InputSection &isec) const {
addSyntheticLocal("$a", STT_NOTYPE, 0, 0, isec);
addSyntheticLocal("$d", STT_NOTYPE, 16, 0, isec);
}
// Long form PLT entries that do not have any restrictions on the displacement
// of the .plt from the .plt.got.
static void writePltLong(uint8_t *buf, uint64_t gotPltEntryAddr,
uint64_t pltEntryAddr) {
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);
}
// The default PLT entries require the .plt.got to be within 128 Mb of the
// .plt in the positive direction.
void ARM::writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const {
// The PLT entry is similar to the example given in Appendix A of ELF for
// the Arm Architecture. Instead of using the Group Relocations to find the
// optimal rotation for the 8-bit immediate used in the add instructions we
// hard code the most compact rotations for simplicity. This saves a load
// instruction over the long plt sequences.
const uint32_t pltData[] = {
0xe28fc600, // L1: add ip, pc, #0x0NN00000 Offset(&(.plt.got) - L1 - 8
0xe28cca00, // add ip, ip, #0x000NN000 Offset(&(.plt.got) - L1 - 8
0xe5bcf000, // ldr pc, [ip, #0x00000NNN] Offset(&(.plt.got) - L1 - 8
};
uint64_t offset = sym.getGotPltVA() - pltEntryAddr - 8;
if (!llvm::isUInt<27>(offset)) {
// We cannot encode the Offset, use the long form.
writePltLong(buf, sym.getGotPltVA(), pltEntryAddr);
return;
}
write32le(buf + 0, pltData[0] | ((offset >> 20) & 0xff));
write32le(buf + 4, pltData[1] | ((offset >> 12) & 0xff));
write32le(buf + 8, pltData[2] | (offset & 0xfff));
memcpy(buf + 12, trapInstr.data(), 4); // Pad to 16-byte boundary
}
void ARM::addPltSymbols(InputSection &isec, uint64_t off) const {
addSyntheticLocal("$a", STT_NOTYPE, off, 0, isec);
addSyntheticLocal("$d", STT_NOTYPE, off + 12, 0, isec);
}
bool ARM::needsThunk(RelExpr expr, RelType type, const InputFile *file,
uint64_t branchAddr, const Symbol &s,
int64_t a) const {
// If S is an undefined weak symbol and does not have a PLT entry then it
// will be resolved as a branch to the next instruction.
if (s.isUndefWeak() && !s.isInPlt())
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 (type) {
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 STT_FUNC Symbol has bit 0 set (Thumb).
if (s.isFunc() && expr == R_PC && (s.getVA() & 1))
return true;
LLVM_FALLTHROUGH;
case R_ARM_CALL: {
uint64_t dst = (expr == R_PLT_PC) ? s.getPltVA() : s.getVA();
return !inBranchRange(type, branchAddr, dst + a);
}
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 STT_FUNC Symbol has bit 0 clear (ARM).
if (expr == R_PLT_PC || (s.isFunc() && (s.getVA() & 1) == 0))
return true;
LLVM_FALLTHROUGH;
case R_ARM_THM_CALL: {
uint64_t dst = (expr == R_PLT_PC) ? s.getPltVA() : s.getVA();
return !inBranchRange(type, branchAddr, dst + a);
}
}
return false;
}
uint32_t ARM::getThunkSectionSpacing() const {
// The placing of pre-created ThunkSections is controlled by the value
// thunkSectionSpacing returned by getThunkSectionSpacing(). The aim is to
// place the ThunkSection such that all branches from the InputSections
// prior to the ThunkSection can reach a Thunk placed at the end of the
// ThunkSection. Graphically:
// | up to thunkSectionSpacing .text input sections |
// | ThunkSection |
// | up to thunkSectionSpacing .text input sections |
// | ThunkSection |
// Pre-created ThunkSections are spaced roughly 16MiB apart on ARMv7. This
// is to match the most common expected case of a Thumb 2 encoded BL, BLX or
// B.W:
// ARM B, BL, BLX range +/- 32MiB
// Thumb B.W, BL, BLX range +/- 16MiB
// Thumb B<cc>.W range +/- 1MiB
// If a branch cannot reach a pre-created ThunkSection a new one will be
// created so we can handle the rare cases of a Thumb 2 conditional branch.
// We intentionally use a lower size for thunkSectionSpacing than the maximum
// branch range so the end of the ThunkSection is more likely to be within
// range of the branch instruction that is furthest away. The value we shorten
// thunkSectionSpacing by is set conservatively to allow us to create 16,384
// 12 byte Thunks at any offset in a ThunkSection without risk of a branch to
// one of the Thunks going out of range.
// On Arm the thunkSectionSpacing depends on the range of the Thumb Branch
// range. On earlier Architectures such as ARMv4, ARMv5 and ARMv6 (except
// ARMv6T2) the range is +/- 4MiB.
return (config->armJ1J2BranchEncoding) ? 0x1000000 - 0x30000
: 0x400000 - 0x7500;
}
bool ARM::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
if ((dst & 0x1) == 0)
// Destination is ARM, if ARM caller then Src is already 4-byte aligned.
// If Thumb Caller (BLX) the Src address has bottom 2 bits cleared to ensure
// destination will be 4 byte aligned.
src &= ~0x3;
else
// Bit 0 == 1 denotes Thumb state, it is not part of the range.
dst &= ~0x1;
int64_t offset = dst - src;
switch (type) {
case R_ARM_PC24:
case R_ARM_PLT32:
case R_ARM_JUMP24:
case R_ARM_CALL:
return llvm::isInt<26>(offset);
case R_ARM_THM_JUMP19:
return llvm::isInt<21>(offset);
case R_ARM_THM_JUMP24:
case R_ARM_THM_CALL:
return config->armJ1J2BranchEncoding ? llvm::isInt<25>(offset)
: llvm::isInt<23>(offset);
default:
return true;
}
}
// Helper to produce message text when LLD detects that a CALL relocation to
// a non STT_FUNC symbol that may result in incorrect interworking between ARM
// or Thumb.
static void stateChangeWarning(uint8_t *loc, RelType relt, const Symbol &s) {
assert(!s.isFunc());
const ErrorPlace place = getErrorPlace(loc);
std::string hint;
if (!place.srcLoc.empty())
hint = "; " + place.srcLoc;
if (s.isSection()) {
// Section symbols must be defined and in a section. Users cannot change
// the type. Use the section name as getName() returns an empty string.
warn(place.loc + "branch and link relocation: " + toString(relt) +
" to STT_SECTION symbol " + cast<Defined>(s).section->name +
" ; interworking not performed" + hint);
} else {
// Warn with hint on how to alter the symbol type.
warn(getErrorLocation(loc) + "branch and link relocation: " +
toString(relt) + " to non STT_FUNC symbol: " + s.getName() +
" interworking not performed; consider using directive '.type " +
s.getName() +
", %function' to give symbol type STT_FUNC if interworking between "
"ARM and Thumb is required" +
hint);
}
}
// Rotate a 32-bit unsigned value right by a specified amt of bits.
static uint32_t rotr32(uint32_t val, uint32_t amt) {
assert(amt < 32 && "Invalid rotate amount");
return (val >> amt) | (val << ((32 - amt) & 31));
}
static std::pair<uint32_t, uint32_t> getRemAndLZForGroup(unsigned group,
uint32_t val) {
uint32_t rem, lz;
do {
lz = llvm::countLeadingZeros(val) & ~1;
rem = val;
if (lz == 32) // implies rem == 0
break;
val &= 0xffffff >> lz;
} while (group--);
return {rem, lz};
}
static void encodeAluGroup(uint8_t *loc, const Relocation &rel, uint64_t val,
int group, bool check) {
// ADD/SUB (immediate) add = bit23, sub = bit22
// immediate field carries is a 12-bit modified immediate, made up of a 4-bit
// even rotate right and an 8-bit immediate.
uint32_t opcode = 0x00800000;
if (val >> 63) {
opcode = 0x00400000;
val = -val;
}
uint32_t imm, lz;
std::tie(imm, lz) = getRemAndLZForGroup(group, val);
uint32_t rot = 0;
if (lz < 24) {
imm = rotr32(imm, 24 - lz);
rot = (lz + 8) << 7;
}
if (check && imm > 0xff)
error(getErrorLocation(loc) + "unencodeable immediate " + Twine(val).str() +
" for relocation " + toString(rel.type));
write32le(loc, (read32le(loc) & 0xff3ff000) | opcode | rot | (imm & 0xff));
}
static void encodeLdrGroup(uint8_t *loc, const Relocation &rel, uint64_t val,
int group) {
// R_ARM_LDR_PC_Gn is S + A - P, we have ((S + A) | T) - P, if S is a
// function then addr is 0 (modulo 2) and Pa is 0 (modulo 4) so we can clear
// bottom bit to recover S + A - P.
if (rel.sym->isFunc())
val &= ~0x1;
// LDR (literal) u = bit23
uint32_t opcode = 0x00800000;
if (val >> 63) {
opcode = 0x0;
val = -val;
}
uint32_t imm = getRemAndLZForGroup(group, val).first;
checkUInt(loc, imm, 12, rel);
write32le(loc, (read32le(loc) & 0xff7ff000) | opcode | imm);
}
static void encodeLdrsGroup(uint8_t *loc, const Relocation &rel, uint64_t val,
int group) {
// R_ARM_LDRS_PC_Gn is S + A - P, we have ((S + A) | T) - P, if S is a
// function then addr is 0 (modulo 2) and Pa is 0 (modulo 4) so we can clear
// bottom bit to recover S + A - P.
if (rel.sym->isFunc())
val &= ~0x1;
// LDRD/LDRH/LDRSB/LDRSH (literal) u = bit23
uint32_t opcode = 0x00800000;
if (val >> 63) {
opcode = 0x0;
val = -val;
}
uint32_t imm = getRemAndLZForGroup(group, val).first;
checkUInt(loc, imm, 8, rel);
write32le(loc, (read32le(loc) & 0xff7ff0f0) | opcode | ((imm & 0xf0) << 4) |
(imm & 0xf));
}
void ARM::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
switch (rel.type) {
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_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_PREL31:
checkInt(loc, val, 31, rel);
write32le(loc, (read32le(loc) & 0x80000000) | (val & ~0x80000000));
break;
case R_ARM_CALL: {
// R_ARM_CALL is used for BL and BLX instructions, for symbols of type
// STT_FUNC we choose whether to write a BL or BLX depending on the
// value of bit 0 of Val. With bit 0 == 1 denoting Thumb. If the symbol is
// not of type STT_FUNC then we must preserve the original instruction.
// PLT entries are always ARM state so we know we don't need to interwork.
assert(rel.sym); // R_ARM_CALL is always reached via relocate().
bool bit0Thumb = val & 1;
bool isBlx = (read32le(loc) & 0xfe000000) == 0xfa000000;
// lld 10.0 and before always used bit0Thumb when deciding to write a BLX
// even when type not STT_FUNC.
if (!rel.sym->isFunc() && isBlx != bit0Thumb)
stateChangeWarning(loc, rel.type, *rel.sym);
if (rel.sym->isFunc() ? bit0Thumb : isBlx) {
// The BLX encoding is 0xfa:H:imm24 where Val = imm24:H:'1'
checkInt(loc, val, 26, rel);
write32le(loc, 0xfa000000 | // opcode
((val & 2) << 23) | // H
((val >> 2) & 0x00ffffff)); // imm24
break;
}
// 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(loc, val, 26, rel);
write32le(loc, (read32le(loc) & ~0x00ffffff) | ((val >> 2) & 0x00ffffff));
break;
case R_ARM_THM_JUMP8:
// We do a 9 bit check because val is right-shifted by 1 bit.
checkInt(loc, val, 9, rel);
write16le(loc, (read32le(loc) & 0xff00) | ((val >> 1) & 0x00ff));
break;
case R_ARM_THM_JUMP11:
// We do a 12 bit check because val is right-shifted by 1 bit.
checkInt(loc, val, 12, rel);
write16le(loc, (read32le(loc) & 0xf800) | ((val >> 1) & 0x07ff));
break;
case R_ARM_THM_JUMP19:
// Encoding T3: Val = S:J2:J1:imm6:imm11:0
checkInt(loc, val, 21, rel);
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, for symbols of type
// STT_FUNC we choose whether to write a BL or BLX depending on the
// value of bit 0 of Val. With bit 0 == 0 denoting ARM, if the symbol is
// not of type STT_FUNC then we must preserve the original instruction.
// PLT entries are always ARM state so we know we need to interwork.
assert(rel.sym); // R_ARM_THM_CALL is always reached via relocate().
bool bit0Thumb = val & 1;
bool isBlx = (read16le(loc + 2) & 0x1000) == 0;
// lld 10.0 and before always used bit0Thumb when deciding to write a BLX
// even when type not STT_FUNC. PLT entries generated by LLD are always ARM.
if (!rel.sym->isFunc() && !rel.sym->isInPlt() && isBlx == bit0Thumb)
stateChangeWarning(loc, rel.type, *rel.sym);
if (rel.sym->isFunc() || rel.sym->isInPlt() ? !bit0Thumb : isBlx) {
// We are writing a BLX. Ensure BLX destination is 4-byte aligned. As
// the BLX instruction may only be two byte aligned. This must be done
// before overflow check.
val = alignTo(val, 4);
write16le(loc + 2, read16le(loc + 2) & ~0x1000);
} else {
write16le(loc + 2, (read16le(loc + 2) & ~0x1000) | 1 << 12);
}
if (!config->armJ1J2BranchEncoding) {
// Older Arm architectures do not support R_ARM_THM_JUMP24 and have
// different encoding rules and range due to J1 and J2 always being 1.
checkInt(loc, val, 23, rel);
write16le(loc,
0xf000 | // opcode
((val >> 12) & 0x07ff)); // imm11
write16le(loc + 2,
(read16le(loc + 2) & 0xd000) | // opcode
0x2800 | // J1 == J2 == 1
((val >> 1) & 0x07ff)); // imm11
break;
}
}
// 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
checkInt(loc, val, 25, rel);
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:
case R_ARM_MOVW_BREL_NC:
write32le(loc, (read32le(loc) & ~0x000f0fff) | ((val & 0xf000) << 4) |
(val & 0x0fff));
break;
case R_ARM_MOVT_ABS:
case R_ARM_MOVT_PREL:
case R_ARM_MOVT_BREL:
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:
case R_ARM_THM_MOVT_BREL:
// Encoding T1: A = imm4:i:imm3:imm8
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:
case R_ARM_THM_MOVW_BREL_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;
case R_ARM_ALU_PC_G0:
encodeAluGroup(loc, rel, val, 0, true);
break;
case R_ARM_ALU_PC_G0_NC:
encodeAluGroup(loc, rel, val, 0, false);
break;
case R_ARM_ALU_PC_G1:
encodeAluGroup(loc, rel, val, 1, true);
break;
case R_ARM_ALU_PC_G1_NC:
encodeAluGroup(loc, rel, val, 1, false);
break;
case R_ARM_ALU_PC_G2:
encodeAluGroup(loc, rel, val, 2, true);
break;
case R_ARM_LDR_PC_G0:
encodeLdrGroup(loc, rel, val, 0);
break;
case R_ARM_LDR_PC_G1:
encodeLdrGroup(loc, rel, val, 1);
break;
case R_ARM_LDR_PC_G2:
encodeLdrGroup(loc, rel, val, 2);
break;
case R_ARM_LDRS_PC_G0:
encodeLdrsGroup(loc, rel, val, 0);
break;
case R_ARM_LDRS_PC_G1:
encodeLdrsGroup(loc, rel, val, 1);
break;
case R_ARM_LDRS_PC_G2:
encodeLdrsGroup(loc, rel, val, 2);
break;
case R_ARM_THM_ALU_PREL_11_0: {
// ADR encoding T2 (sub), T3 (add) i:imm3:imm8
int64_t imm = val;
uint16_t sub = 0;
if (imm < 0) {
imm = -imm;
sub = 0x00a0;
}
checkUInt(loc, imm, 12, rel);
write16le(loc, (read16le(loc) & 0xfb0f) | sub | (imm & 0x800) >> 1);
write16le(loc + 2,
(read16le(loc + 2) & 0x8f00) | (imm & 0x700) << 4 | (imm & 0xff));
break;
}
case R_ARM_THM_PC8:
// ADR and LDR literal encoding T1 positive offset only imm8:00
// R_ARM_THM_PC8 is S + A - Pa, we have ((S + A) | T) - Pa, if S is a
// function then addr is 0 (modulo 2) and Pa is 0 (modulo 4) so we can clear
// bottom bit to recover S + A - Pa.
if (rel.sym->isFunc())
val &= ~0x1;
checkUInt(loc, val, 10, rel);
checkAlignment(loc, val, 4, rel);
write16le(loc, (read16le(loc) & 0xff00) | (val & 0x3fc) >> 2);
break;
case R_ARM_THM_PC12: {
// LDR (literal) encoding T2, add = (U == '1') imm12
// imm12 is unsigned
// R_ARM_THM_PC12 is S + A - Pa, we have ((S + A) | T) - Pa, if S is a
// function then addr is 0 (modulo 2) and Pa is 0 (modulo 4) so we can clear
// bottom bit to recover S + A - Pa.
if (rel.sym->isFunc())
val &= ~0x1;
int64_t imm12 = val;
uint16_t u = 0x0080;
if (imm12 < 0) {
imm12 = -imm12;
u = 0;
}
checkUInt(loc, imm12, 12, rel);
write16le(loc, read16le(loc) | u);
write16le(loc + 2, (read16le(loc + 2) & 0xf000) | imm12);
break;
}
default:
llvm_unreachable("unknown relocation");
}
}
int64_t ARM::getImplicitAddend(const uint8_t *buf, RelType type) const {
switch (type) {
default:
internalLinkerError(getErrorLocation(buf),
"cannot read addend for relocation " + toString(type));
return 0;
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_IRELATIVE:
case R_ARM_REL32:
case R_ARM_RELATIVE:
case R_ARM_SBREL32:
case R_ARM_TARGET1:
case R_ARM_TARGET2:
case R_ARM_TLS_DTPMOD32:
case R_ARM_TLS_DTPOFF32:
case R_ARM_TLS_GD32:
case R_ARM_TLS_IE32:
case R_ARM_TLS_LDM32:
case R_ARM_TLS_LE32:
case R_ARM_TLS_LDO32:
case R_ARM_TLS_TPOFF32:
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_JUMP8:
return SignExtend64<9>(read16le(buf) << 1);
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:
if (!config->armJ1J2BranchEncoding) {
// Older Arm architectures do not support R_ARM_THM_JUMP24 and have
// different encoding rules and range due to J1 and J2 always being 1.
uint16_t hi = read16le(buf);
uint16_t lo = read16le(buf + 2);
return SignExtend64<22>(((hi & 0x7ff) << 12) | // imm11
((lo & 0x7ff) << 1)); // imm11:0
break;
}
LLVM_FALLTHROUGH;
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)
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:
case R_ARM_MOVW_BREL_NC:
case R_ARM_MOVT_BREL: {
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:
case R_ARM_THM_MOVW_BREL_NC:
case R_ARM_THM_MOVT_BREL: {
// 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
}
case R_ARM_ALU_PC_G0:
case R_ARM_ALU_PC_G0_NC:
case R_ARM_ALU_PC_G1:
case R_ARM_ALU_PC_G1_NC:
case R_ARM_ALU_PC_G2: {
// 12-bit immediate is a modified immediate made up of a 4-bit even
// right rotation and 8-bit constant. After the rotation the value
// is zero-extended. When bit 23 is set the instruction is an add, when
// bit 22 is set it is a sub.
uint32_t instr = read32le(buf);
uint32_t val = rotr32(instr & 0xff, ((instr & 0xf00) >> 8) * 2);
return (instr & 0x00400000) ? -val : val;
}
case R_ARM_LDR_PC_G0:
case R_ARM_LDR_PC_G1:
case R_ARM_LDR_PC_G2: {
// ADR (literal) add = bit23, sub = bit22
// LDR (literal) u = bit23 unsigned imm12
bool u = read32le(buf) & 0x00800000;
uint32_t imm12 = read32le(buf) & 0xfff;
return u ? imm12 : -imm12;
}
case R_ARM_LDRS_PC_G0:
case R_ARM_LDRS_PC_G1:
case R_ARM_LDRS_PC_G2: {
// LDRD/LDRH/LDRSB/LDRSH (literal) u = bit23 unsigned imm8
uint32_t opcode = read32le(buf);
bool u = opcode & 0x00800000;
uint32_t imm4l = opcode & 0xf;
uint32_t imm4h = (opcode & 0xf00) >> 4;
return u ? (imm4h | imm4l) : -(imm4h | imm4l);
}
case R_ARM_THM_ALU_PREL_11_0: {
// Thumb2 ADR, which is an alias for a sub or add instruction with an
// unsigned immediate.
// ADR encoding T2 (sub), T3 (add) i:imm3:imm8
uint16_t hi = read16le(buf);
uint16_t lo = read16le(buf + 2);
uint64_t imm = (hi & 0x0400) << 1 | // i
(lo & 0x7000) >> 4 | // imm3
(lo & 0x00ff); // imm8
// For sub, addend is negative, add is positive.
return (hi & 0x00f0) ? -imm : imm;
}
case R_ARM_THM_PC8:
// ADR and LDR (literal) encoding T1
// From ELF for the ARM Architecture the initial signed addend is formed
// from an unsigned field using expression (((imm8:00 + 4) & 0x3ff) – 4)
// this trick permits the PC bias of -4 to be encoded using imm8 = 0xff
return ((((read16le(buf) & 0xff) << 2) + 4) & 0x3ff) - 4;
case R_ARM_THM_PC12: {
// LDR (literal) encoding T2, add = (U == '1') imm12
bool u = read16le(buf) & 0x0080;
uint64_t imm12 = read16le(buf + 2) & 0x0fff;
return u ? imm12 : -imm12;
}
case R_ARM_NONE:
case R_ARM_V4BX:
case R_ARM_JUMP_SLOT:
// These relocations are defined as not having an implicit addend.
return 0;
}
}
TargetInfo *elf::getARMTargetInfo() {
static ARM target;
return &target;
}
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