//===- X86_64.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 "lld/Common/ErrorHandler.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::ELF;
namespace lld {
namespace elf {
namespace {
class X86_64 : public TargetInfo {
public:
X86_64();
int getTlsGdRelaxSkip(RelType type) const override;
RelExpr getRelExpr(RelType type, const Symbol &s,
const uint8_t *loc) const override;
RelType getDynRel(RelType type) const override;
void writeGotPltHeader(uint8_t *buf) const override;
void writeGotPlt(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 relocateOne(uint8_t *loc, RelType type, uint64_t val) const override;
RelExpr adjustRelaxExpr(RelType type, const uint8_t *data,
RelExpr expr) const override;
void relaxGot(uint8_t *loc, RelType type, uint64_t val) const override;
void relaxTlsGdToIe(uint8_t *loc, RelType type, uint64_t val) const override;
void relaxTlsGdToLe(uint8_t *loc, RelType type, uint64_t val) const override;
void relaxTlsIeToLe(uint8_t *loc, RelType type, uint64_t val) const override;
void relaxTlsLdToLe(uint8_t *loc, RelType type, uint64_t val) const override;
bool adjustPrologueForCrossSplitStack(uint8_t *loc, uint8_t *end,
uint8_t stOther) const override;
};
} // namespace
X86_64::X86_64() {
copyRel = R_X86_64_COPY;
gotRel = R_X86_64_GLOB_DAT;
noneRel = R_X86_64_NONE;
pltRel = R_X86_64_JUMP_SLOT;
relativeRel = R_X86_64_RELATIVE;
iRelativeRel = R_X86_64_IRELATIVE;
symbolicRel = R_X86_64_64;
tlsDescRel = R_X86_64_TLSDESC;
tlsGotRel = R_X86_64_TPOFF64;
tlsModuleIndexRel = R_X86_64_DTPMOD64;
tlsOffsetRel = R_X86_64_DTPOFF64;
pltHeaderSize = 16;
pltEntrySize = 16;
ipltEntrySize = 16;
trapInstr = {0xcc, 0xcc, 0xcc, 0xcc}; // 0xcc = INT3
// Align to the large page size (known as a superpage or huge page).
// FreeBSD automatically promotes large, superpage-aligned allocations.
defaultImageBase = 0x200000;
}
int X86_64::getTlsGdRelaxSkip(RelType type) const { return 2; }
RelExpr X86_64::getRelExpr(RelType type, const Symbol &s,
const uint8_t *loc) const {
if (type == R_X86_64_GOTTPOFF)
config->hasStaticTlsModel = true;
switch (type) {
case R_X86_64_8:
case R_X86_64_16:
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
return R_ABS;
case R_X86_64_DTPOFF32:
case R_X86_64_DTPOFF64:
return R_DTPREL;
case R_X86_64_TPOFF32:
return R_TLS;
case R_X86_64_TLSDESC_CALL:
return R_TLSDESC_CALL;
case R_X86_64_TLSLD:
return R_TLSLD_PC;
case R_X86_64_TLSGD:
return R_TLSGD_PC;
case R_X86_64_SIZE32:
case R_X86_64_SIZE64:
return R_SIZE;
case R_X86_64_PLT32:
return R_PLT_PC;
case R_X86_64_PC8:
case R_X86_64_PC16:
case R_X86_64_PC32:
case R_X86_64_PC64:
return R_PC;
case R_X86_64_GOT32:
case R_X86_64_GOT64:
return R_GOTPLT;
case R_X86_64_GOTPC32_TLSDESC:
return R_TLSDESC_PC;
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_REX_GOTPCRELX:
case R_X86_64_GOTTPOFF:
return R_GOT_PC;
case R_X86_64_GOTOFF64:
return R_GOTPLTREL;
case R_X86_64_GOTPC32:
case R_X86_64_GOTPC64:
return R_GOTPLTONLY_PC;
case R_X86_64_NONE:
return R_NONE;
default:
error(getErrorLocation(loc) + "unknown relocation (" + Twine(type) +
") against symbol " + toString(s));
return R_NONE;
}
}
void X86_64::writeGotPltHeader(uint8_t *buf) const {
// The first entry holds the value of _DYNAMIC. It is not clear why that is
// required, but it is documented in the psabi and the glibc dynamic linker
// seems to use it (note that this is relevant for linking ld.so, not any
// other program).
write64le(buf, mainPart->dynamic->getVA());
}
void X86_64::writeGotPlt(uint8_t *buf, const Symbol &s) const {
// See comments in X86::writeGotPlt.
write64le(buf, s.getPltVA() + 6);
}
void X86_64::writePltHeader(uint8_t *buf) const {
const uint8_t pltData[] = {
0xff, 0x35, 0, 0, 0, 0, // pushq GOTPLT+8(%rip)
0xff, 0x25, 0, 0, 0, 0, // jmp *GOTPLT+16(%rip)
0x0f, 0x1f, 0x40, 0x00, // nop
};
memcpy(buf, pltData, sizeof(pltData));
uint64_t gotPlt = in.gotPlt->getVA();
uint64_t plt = in.ibtPlt ? in.ibtPlt->getVA() : in.plt->getVA();
write32le(buf + 2, gotPlt - plt + 2); // GOTPLT+8
write32le(buf + 8, gotPlt - plt + 4); // GOTPLT+16
}
void X86_64::writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const {
const uint8_t inst[] = {
0xff, 0x25, 0, 0, 0, 0, // jmpq *got(%rip)
0x68, 0, 0, 0, 0, // pushq <relocation index>
0xe9, 0, 0, 0, 0, // jmpq plt[0]
};
memcpy(buf, inst, sizeof(inst));
write32le(buf + 2, sym.getGotPltVA() - pltEntryAddr - 6);
write32le(buf + 7, sym.pltIndex);
write32le(buf + 12, in.plt->getVA() - pltEntryAddr - 16);
}
RelType X86_64::getDynRel(RelType type) const {
if (type == R_X86_64_64 || type == R_X86_64_PC64 || type == R_X86_64_SIZE32 ||
type == R_X86_64_SIZE64)
return type;
return R_X86_64_NONE;
}
void X86_64::relaxTlsGdToLe(uint8_t *loc, RelType type, uint64_t val) const {
if (type == R_X86_64_TLSGD) {
// Convert
// .byte 0x66
// leaq x@tlsgd(%rip), %rdi
// .word 0x6666
// rex64
// call __tls_get_addr@plt
// to the following two instructions.
const uint8_t inst[] = {
0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00,
0x00, 0x00, // mov %fs:0x0,%rax
0x48, 0x8d, 0x80, 0, 0, 0, 0, // lea x@tpoff,%rax
};
memcpy(loc - 4, inst, sizeof(inst));
// The original code used a pc relative relocation and so we have to
// compensate for the -4 in had in the addend.
write32le(loc + 8, val + 4);
} else {
// Convert
// lea x@tlsgd(%rip), %rax
// call *(%rax)
// to the following two instructions.
assert(type == R_X86_64_GOTPC32_TLSDESC);
if (memcmp(loc - 3, "\x48\x8d\x05", 3)) {
error(getErrorLocation(loc - 3) + "R_X86_64_GOTPC32_TLSDESC must be used "
"in callq *x@tlsdesc(%rip), %rax");
return;
}
// movq $x@tpoff(%rip),%rax
loc[-2] = 0xc7;
loc[-1] = 0xc0;
write32le(loc, val + 4);
// xchg ax,ax
loc[4] = 0x66;
loc[5] = 0x90;
}
}
void X86_64::relaxTlsGdToIe(uint8_t *loc, RelType type, uint64_t val) const {
if (type == R_X86_64_TLSGD) {
// Convert
// .byte 0x66
// leaq x@tlsgd(%rip), %rdi
// .word 0x6666
// rex64
// call __tls_get_addr@plt
// to the following two instructions.
const uint8_t inst[] = {
0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00,
0x00, 0x00, // mov %fs:0x0,%rax
0x48, 0x03, 0x05, 0, 0, 0, 0, // addq x@gottpoff(%rip),%rax
};
memcpy(loc - 4, inst, sizeof(inst));
// Both code sequences are PC relatives, but since we are moving the
// constant forward by 8 bytes we have to subtract the value by 8.
write32le(loc + 8, val - 8);
} else {
// Convert
// lea x@tlsgd(%rip), %rax
// call *(%rax)
// to the following two instructions.
assert(type == R_X86_64_GOTPC32_TLSDESC);
if (memcmp(loc - 3, "\x48\x8d\x05", 3)) {
error(getErrorLocation(loc - 3) + "R_X86_64_GOTPC32_TLSDESC must be used "
"in callq *x@tlsdesc(%rip), %rax");
return;
}
// movq x@gottpoff(%rip),%rax
loc[-2] = 0x8b;
write32le(loc, val);
// xchg ax,ax
loc[4] = 0x66;
loc[5] = 0x90;
}
}
// In some conditions, R_X86_64_GOTTPOFF relocation can be optimized to
// R_X86_64_TPOFF32 so that it does not use GOT.
void X86_64::relaxTlsIeToLe(uint8_t *loc, RelType type, uint64_t val) const {
uint8_t *inst = loc - 3;
uint8_t reg = loc[-1] >> 3;
uint8_t *regSlot = loc - 1;
// Note that ADD with RSP or R12 is converted to ADD instead of LEA
// because LEA with these registers needs 4 bytes to encode and thus
// wouldn't fit the space.
if (memcmp(inst, "\x48\x03\x25", 3) == 0) {
// "addq foo@gottpoff(%rip),%rsp" -> "addq $foo,%rsp"
memcpy(inst, "\x48\x81\xc4", 3);
} else if (memcmp(inst, "\x4c\x03\x25", 3) == 0) {
// "addq foo@gottpoff(%rip),%r12" -> "addq $foo,%r12"
memcpy(inst, "\x49\x81\xc4", 3);
} else if (memcmp(inst, "\x4c\x03", 2) == 0) {
// "addq foo@gottpoff(%rip),%r[8-15]" -> "leaq foo(%r[8-15]),%r[8-15]"
memcpy(inst, "\x4d\x8d", 2);
*regSlot = 0x80 | (reg << 3) | reg;
} else if (memcmp(inst, "\x48\x03", 2) == 0) {
// "addq foo@gottpoff(%rip),%reg -> "leaq foo(%reg),%reg"
memcpy(inst, "\x48\x8d", 2);
*regSlot = 0x80 | (reg << 3) | reg;
} else if (memcmp(inst, "\x4c\x8b", 2) == 0) {
// "movq foo@gottpoff(%rip),%r[8-15]" -> "movq $foo,%r[8-15]"
memcpy(inst, "\x49\xc7", 2);
*regSlot = 0xc0 | reg;
} else if (memcmp(inst, "\x48\x8b", 2) == 0) {
// "movq foo@gottpoff(%rip),%reg" -> "movq $foo,%reg"
memcpy(inst, "\x48\xc7", 2);
*regSlot = 0xc0 | reg;
} else {
error(getErrorLocation(loc - 3) +
"R_X86_64_GOTTPOFF must be used in MOVQ or ADDQ instructions only");
}
// The original code used a PC relative relocation.
// Need to compensate for the -4 it had in the addend.
write32le(loc, val + 4);
}
void X86_64::relaxTlsLdToLe(uint8_t *loc, RelType type, uint64_t val) const {
if (type == R_X86_64_DTPOFF64) {
write64le(loc, val);
return;
}
if (type == R_X86_64_DTPOFF32) {
write32le(loc, val);
return;
}
const uint8_t inst[] = {
0x66, 0x66, // .word 0x6666
0x66, // .byte 0x66
0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00, // mov %fs:0,%rax
};
if (loc[4] == 0xe8) {
// Convert
// leaq bar@tlsld(%rip), %rdi # 48 8d 3d <Loc>
// callq __tls_get_addr@PLT # e8 <disp32>
// leaq bar@dtpoff(%rax), %rcx
// to
// .word 0x6666
// .byte 0x66
// mov %fs:0,%rax
// leaq bar@tpoff(%rax), %rcx
memcpy(loc - 3, inst, sizeof(inst));
return;
}
if (loc[4] == 0xff && loc[5] == 0x15) {
// Convert
// leaq x@tlsld(%rip),%rdi # 48 8d 3d <Loc>
// call *__tls_get_addr@GOTPCREL(%rip) # ff 15 <disp32>
// to
// .long 0x66666666
// movq %fs:0,%rax
// See "Table 11.9: LD -> LE Code Transition (LP64)" in
// https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/x86-64-psABI-1.0.pdf
loc[-3] = 0x66;
memcpy(loc - 2, inst, sizeof(inst));
return;
}
error(getErrorLocation(loc - 3) +
"expected R_X86_64_PLT32 or R_X86_64_GOTPCRELX after R_X86_64_TLSLD");
}
void X86_64::relocateOne(uint8_t *loc, RelType type, uint64_t val) const {
switch (type) {
case R_X86_64_8:
checkIntUInt(loc, val, 8, type);
*loc = val;
break;
case R_X86_64_PC8:
checkInt(loc, val, 8, type);
*loc = val;
break;
case R_X86_64_16:
checkIntUInt(loc, val, 16, type);
write16le(loc, val);
break;
case R_X86_64_PC16:
checkInt(loc, val, 16, type);
write16le(loc, val);
break;
case R_X86_64_32:
checkUInt(loc, val, 32, type);
write32le(loc, val);
break;
case R_X86_64_32S:
case R_X86_64_TPOFF32:
case R_X86_64_GOT32:
case R_X86_64_GOTPC32:
case R_X86_64_GOTPC32_TLSDESC:
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_REX_GOTPCRELX:
case R_X86_64_PC32:
case R_X86_64_GOTTPOFF:
case R_X86_64_PLT32:
case R_X86_64_TLSGD:
case R_X86_64_TLSLD:
case R_X86_64_DTPOFF32:
case R_X86_64_SIZE32:
checkInt(loc, val, 32, type);
write32le(loc, val);
break;
case R_X86_64_64:
case R_X86_64_DTPOFF64:
case R_X86_64_PC64:
case R_X86_64_SIZE64:
case R_X86_64_GOT64:
case R_X86_64_GOTOFF64:
case R_X86_64_GOTPC64:
write64le(loc, val);
break;
default:
llvm_unreachable("unknown relocation");
}
}
RelExpr X86_64::adjustRelaxExpr(RelType type, const uint8_t *data,
RelExpr relExpr) const {
if (type != R_X86_64_GOTPCRELX && type != R_X86_64_REX_GOTPCRELX)
return relExpr;
const uint8_t op = data[-2];
const uint8_t modRm = data[-1];
// FIXME: When PIC is disabled and foo is defined locally in the
// lower 32 bit address space, memory operand in mov can be converted into
// immediate operand. Otherwise, mov must be changed to lea. We support only
// latter relaxation at this moment.
if (op == 0x8b)
return R_RELAX_GOT_PC;
// Relax call and jmp.
if (op == 0xff && (modRm == 0x15 || modRm == 0x25))
return R_RELAX_GOT_PC;
// Relaxation of test, adc, add, and, cmp, or, sbb, sub, xor.
// If PIC then no relaxation is available.
// We also don't relax test/binop instructions without REX byte,
// they are 32bit operations and not common to have.
assert(type == R_X86_64_REX_GOTPCRELX);
return config->isPic ? relExpr : R_RELAX_GOT_PC_NOPIC;
}
// A subset of relaxations can only be applied for no-PIC. This method
// handles such relaxations. Instructions encoding information was taken from:
// "Intel 64 and IA-32 Architectures Software Developer's Manual V2"
// (http://www.intel.com/content/dam/www/public/us/en/documents/manuals/
// 64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf)
static void relaxGotNoPic(uint8_t *loc, uint64_t val, uint8_t op,
uint8_t modRm) {
const uint8_t rex = loc[-3];
// Convert "test %reg, foo@GOTPCREL(%rip)" to "test $foo, %reg".
if (op == 0x85) {
// See "TEST-Logical Compare" (4-428 Vol. 2B),
// TEST r/m64, r64 uses "full" ModR / M byte (no opcode extension).
// ModR/M byte has form XX YYY ZZZ, where
// YYY is MODRM.reg(register 2), ZZZ is MODRM.rm(register 1).
// XX has different meanings:
// 00: The operand's memory address is in reg1.
// 01: The operand's memory address is reg1 + a byte-sized displacement.
// 10: The operand's memory address is reg1 + a word-sized displacement.
// 11: The operand is reg1 itself.
// If an instruction requires only one operand, the unused reg2 field
// holds extra opcode bits rather than a register code
// 0xC0 == 11 000 000 binary.
// 0x38 == 00 111 000 binary.
// We transfer reg2 to reg1 here as operand.
// See "2.1.3 ModR/M and SIB Bytes" (Vol. 2A 2-3).
loc[-1] = 0xc0 | (modRm & 0x38) >> 3; // ModR/M byte.
// Change opcode from TEST r/m64, r64 to TEST r/m64, imm32
// See "TEST-Logical Compare" (4-428 Vol. 2B).
loc[-2] = 0xf7;
// Move R bit to the B bit in REX byte.
// REX byte is encoded as 0100WRXB, where
// 0100 is 4bit fixed pattern.
// REX.W When 1, a 64-bit operand size is used. Otherwise, when 0, the
// default operand size is used (which is 32-bit for most but not all
// instructions).
// REX.R This 1-bit value is an extension to the MODRM.reg field.
// REX.X This 1-bit value is an extension to the SIB.index field.
// REX.B This 1-bit value is an extension to the MODRM.rm field or the
// SIB.base field.
// See "2.2.1.2 More on REX Prefix Fields " (2-8 Vol. 2A).
loc[-3] = (rex & ~0x4) | (rex & 0x4) >> 2;
write32le(loc, val);
return;
}
// If we are here then we need to relax the adc, add, and, cmp, or, sbb, sub
// or xor operations.
// Convert "binop foo@GOTPCREL(%rip), %reg" to "binop $foo, %reg".
// Logic is close to one for test instruction above, but we also
// write opcode extension here, see below for details.
loc[-1] = 0xc0 | (modRm & 0x38) >> 3 | (op & 0x3c); // ModR/M byte.
// Primary opcode is 0x81, opcode extension is one of:
// 000b = ADD, 001b is OR, 010b is ADC, 011b is SBB,
// 100b is AND, 101b is SUB, 110b is XOR, 111b is CMP.
// This value was wrote to MODRM.reg in a line above.
// See "3.2 INSTRUCTIONS (A-M)" (Vol. 2A 3-15),
// "INSTRUCTION SET REFERENCE, N-Z" (Vol. 2B 4-1) for
// descriptions about each operation.
loc[-2] = 0x81;
loc[-3] = (rex & ~0x4) | (rex & 0x4) >> 2;
write32le(loc, val);
}
void X86_64::relaxGot(uint8_t *loc, RelType type, uint64_t val) const {
const uint8_t op = loc[-2];
const uint8_t modRm = loc[-1];
// Convert "mov foo@GOTPCREL(%rip),%reg" to "lea foo(%rip),%reg".
if (op == 0x8b) {
loc[-2] = 0x8d;
write32le(loc, val);
return;
}
if (op != 0xff) {
// We are relaxing a rip relative to an absolute, so compensate
// for the old -4 addend.
assert(!config->isPic);
relaxGotNoPic(loc, val + 4, op, modRm);
return;
}
// Convert call/jmp instructions.
if (modRm == 0x15) {
// ABI says we can convert "call *foo@GOTPCREL(%rip)" to "nop; call foo".
// Instead we convert to "addr32 call foo" where addr32 is an instruction
// prefix. That makes result expression to be a single instruction.
loc[-2] = 0x67; // addr32 prefix
loc[-1] = 0xe8; // call
write32le(loc, val);
return;
}
// Convert "jmp *foo@GOTPCREL(%rip)" to "jmp foo; nop".
// jmp doesn't return, so it is fine to use nop here, it is just a stub.
assert(modRm == 0x25);
loc[-2] = 0xe9; // jmp
loc[3] = 0x90; // nop
write32le(loc - 1, val + 1);
}
// A split-stack prologue starts by checking the amount of stack remaining
// in one of two ways:
// A) Comparing of the stack pointer to a field in the tcb.
// B) Or a load of a stack pointer offset with an lea to r10 or r11.
bool X86_64::adjustPrologueForCrossSplitStack(uint8_t *loc, uint8_t *end,
uint8_t stOther) const {
if (!config->is64) {
error("Target doesn't support split stacks.");
return false;
}
if (loc + 8 >= end)
return false;
// Replace "cmp %fs:0x70,%rsp" and subsequent branch
// with "stc, nopl 0x0(%rax,%rax,1)"
if (memcmp(loc, "\x64\x48\x3b\x24\x25", 5) == 0) {
memcpy(loc, "\xf9\x0f\x1f\x84\x00\x00\x00\x00", 8);
return true;
}
// Adjust "lea X(%rsp),%rYY" to lea "(X - 0x4000)(%rsp),%rYY" where rYY could
// be r10 or r11. The lea instruction feeds a subsequent compare which checks
// if there is X available stack space. Making X larger effectively reserves
// that much additional space. The stack grows downward so subtract the value.
if (memcmp(loc, "\x4c\x8d\x94\x24", 4) == 0 ||
memcmp(loc, "\x4c\x8d\x9c\x24", 4) == 0) {
// The offset bytes are encoded four bytes after the start of the
// instruction.
write32le(loc + 4, read32le(loc + 4) - 0x4000);
return true;
}
return false;
}
// If Intel Indirect Branch Tracking is enabled, we have to emit special PLT
// entries containing endbr64 instructions. A PLT entry will be split into two
// parts, one in .plt.sec (writePlt), and the other in .plt (writeIBTPlt).
namespace {
class IntelIBT : public X86_64 {
public:
IntelIBT();
void writeGotPlt(uint8_t *buf, const Symbol &s) const override;
void writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const override;
void writeIBTPlt(uint8_t *buf, size_t numEntries) const override;
static const unsigned IBTPltHeaderSize = 16;
};
} // namespace
IntelIBT::IntelIBT() { pltHeaderSize = 0; }
void IntelIBT::writeGotPlt(uint8_t *buf, const Symbol &s) const {
uint64_t va =
in.ibtPlt->getVA() + IBTPltHeaderSize + s.pltIndex * pltEntrySize;
write64le(buf, va);
}
void IntelIBT::writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const {
const uint8_t Inst[] = {
0xf3, 0x0f, 0x1e, 0xfa, // endbr64
0xff, 0x25, 0, 0, 0, 0, // jmpq *got(%rip)
0x66, 0x0f, 0x1f, 0x44, 0, 0, // nop
};
memcpy(buf, Inst, sizeof(Inst));
write32le(buf + 6, sym.getGotPltVA() - pltEntryAddr - 10);
}
void IntelIBT::writeIBTPlt(uint8_t *buf, size_t numEntries) const {
writePltHeader(buf);
buf += IBTPltHeaderSize;
const uint8_t inst[] = {
0xf3, 0x0f, 0x1e, 0xfa, // endbr64
0x68, 0, 0, 0, 0, // pushq <relocation index>
0xe9, 0, 0, 0, 0, // jmpq plt[0]
0x66, 0x90, // nop
};
for (size_t i = 0; i < numEntries; ++i) {
memcpy(buf, inst, sizeof(inst));
write32le(buf + 5, i);
write32le(buf + 10, -pltHeaderSize - sizeof(inst) * i - 30);
buf += sizeof(inst);
}
}
// These nonstandard PLT entries are to migtigate Spectre v2 security
// vulnerability. In order to mitigate Spectre v2, we want to avoid indirect
// branch instructions such as `jmp *GOTPLT(%rip)`. So, in the following PLT
// entries, we use a CALL followed by MOV and RET to do the same thing as an
// indirect jump. That instruction sequence is so-called "retpoline".
//
// We have two types of retpoline PLTs as a size optimization. If `-z now`
// is specified, all dynamic symbols are resolved at load-time. Thus, when
// that option is given, we can omit code for symbol lazy resolution.
namespace {
class Retpoline : public X86_64 {
public:
Retpoline();
void writeGotPlt(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;
};
class RetpolineZNow : public X86_64 {
public:
RetpolineZNow();
void writeGotPlt(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;
};
} // namespace
Retpoline::Retpoline() {
pltHeaderSize = 48;
pltEntrySize = 32;
ipltEntrySize = 32;
}
void Retpoline::writeGotPlt(uint8_t *buf, const Symbol &s) const {
write64le(buf, s.getPltVA() + 17);
}
void Retpoline::writePltHeader(uint8_t *buf) const {
const uint8_t insn[] = {
0xff, 0x35, 0, 0, 0, 0, // 0: pushq GOTPLT+8(%rip)
0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // 6: mov GOTPLT+16(%rip), %r11
0xe8, 0x0e, 0x00, 0x00, 0x00, // d: callq next
0xf3, 0x90, // 12: loop: pause
0x0f, 0xae, 0xe8, // 14: lfence
0xeb, 0xf9, // 17: jmp loop
0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 19: int3; .align 16
0x4c, 0x89, 0x1c, 0x24, // 20: next: mov %r11, (%rsp)
0xc3, // 24: ret
0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 25: int3; padding
0xcc, 0xcc, 0xcc, 0xcc, // 2c: int3; padding
};
memcpy(buf, insn, sizeof(insn));
uint64_t gotPlt = in.gotPlt->getVA();
uint64_t plt = in.plt->getVA();
write32le(buf + 2, gotPlt - plt - 6 + 8);
write32le(buf + 9, gotPlt - plt - 13 + 16);
}
void Retpoline::writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const {
const uint8_t insn[] = {
0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // 0: mov foo@GOTPLT(%rip), %r11
0xe8, 0, 0, 0, 0, // 7: callq plt+0x20
0xe9, 0, 0, 0, 0, // c: jmp plt+0x12
0x68, 0, 0, 0, 0, // 11: pushq <relocation index>
0xe9, 0, 0, 0, 0, // 16: jmp plt+0
0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 1b: int3; padding
};
memcpy(buf, insn, sizeof(insn));
uint64_t off = pltEntryAddr - in.plt->getVA();
write32le(buf + 3, sym.getGotPltVA() - pltEntryAddr - 7);
write32le(buf + 8, -off - 12 + 32);
write32le(buf + 13, -off - 17 + 18);
write32le(buf + 18, sym.pltIndex);
write32le(buf + 23, -off - 27);
}
RetpolineZNow::RetpolineZNow() {
pltHeaderSize = 32;
pltEntrySize = 16;
ipltEntrySize = 16;
}
void RetpolineZNow::writePltHeader(uint8_t *buf) const {
const uint8_t insn[] = {
0xe8, 0x0b, 0x00, 0x00, 0x00, // 0: call next
0xf3, 0x90, // 5: loop: pause
0x0f, 0xae, 0xe8, // 7: lfence
0xeb, 0xf9, // a: jmp loop
0xcc, 0xcc, 0xcc, 0xcc, // c: int3; .align 16
0x4c, 0x89, 0x1c, 0x24, // 10: next: mov %r11, (%rsp)
0xc3, // 14: ret
0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 15: int3; padding
0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 1a: int3; padding
0xcc, // 1f: int3; padding
};
memcpy(buf, insn, sizeof(insn));
}
void RetpolineZNow::writePlt(uint8_t *buf, const Symbol &sym,
uint64_t pltEntryAddr) const {
const uint8_t insn[] = {
0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // mov foo@GOTPLT(%rip), %r11
0xe9, 0, 0, 0, 0, // jmp plt+0
0xcc, 0xcc, 0xcc, 0xcc, // int3; padding
};
memcpy(buf, insn, sizeof(insn));
write32le(buf + 3, sym.getGotPltVA() - pltEntryAddr - 7);
write32le(buf + 8, in.plt->getVA() - pltEntryAddr - 12);
}
static TargetInfo *getTargetInfo() {
if (config->zRetpolineplt) {
if (config->zNow) {
static RetpolineZNow t;
return &t;
}
static Retpoline t;
return &t;
}
if (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT) {
static IntelIBT t;
return &t;
}
static X86_64 t;
return &t;
}
TargetInfo *getX86_64TargetInfo() { return getTargetInfo(); }
} // namespace elf
} // namespace lld