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//===- EhFrame.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 "EhFrame.h"
#include "InputFiles.h"
#include "lld/Common/ErrorHandler.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace lld;
using namespace lld::macho;
using namespace llvm::support::endian;
uint64_t EhReader::readLength(size_t *off) const {
const size_t errOff = *off;
if (*off + 4 > data.size())
failOn(errOff, "CIE/FDE too small");
uint64_t len = read32le(data.data() + *off);
*off += 4;
if (len == dwarf::DW_LENGTH_DWARF64) {
// FIXME: test this DWARF64 code path
if (*off + 8 > data.size())
failOn(errOff, "CIE/FDE too small");
len = read64le(data.data() + *off);
*off += 8;
}
if (*off + len > data.size())
failOn(errOff, "CIE/FDE extends past the end of the section");
return len;
}
void EhReader::skipValidLength(size_t *off) const {
uint32_t len = read32le(data.data() + *off);
*off += 4;
if (len == dwarf::DW_LENGTH_DWARF64)
*off += 8;
}
// Read a byte and advance off by one byte.
uint8_t EhReader::readByte(size_t *off) const {
if (*off + 1 > data.size())
failOn(*off, "unexpected end of CIE/FDE");
return data[(*off)++];
}
uint32_t EhReader::readU32(size_t *off) const {
if (*off + 4 > data.size())
failOn(*off, "unexpected end of CIE/FDE");
uint32_t v = read32le(data.data() + *off);
*off += 4;
return v;
}
uint64_t EhReader::readPointer(size_t *off, uint8_t size) const {
if (*off + size > data.size())
failOn(*off, "unexpected end of CIE/FDE");
uint64_t v;
if (size == 8)
v = read64le(data.data() + *off);
else {
assert(size == 4);
v = read32le(data.data() + *off);
}
*off += size;
return v;
}
// Read a null-terminated string.
StringRef EhReader::readString(size_t *off) const {
if (*off > data.size())
failOn(*off, "corrupted CIE (failed to read string)");
const size_t maxlen = data.size() - *off;
auto *c = reinterpret_cast<const char *>(data.data() + *off);
size_t len = strnlen(c, maxlen);
if (len == maxlen) // we failed to find the null terminator
failOn(*off, "corrupted CIE (failed to read string)");
*off += len + 1; // skip the null byte too
return StringRef(c, len);
}
void EhReader::skipLeb128(size_t *off) const {
const size_t errOff = *off;
while (*off < data.size()) {
uint8_t val = data[(*off)++];
if ((val & 0x80) == 0)
return;
}
failOn(errOff, "corrupted CIE (failed to read LEB128)");
}
void EhReader::failOn(size_t errOff, const Twine &msg) const {
fatal(toString(file) + ":(__eh_frame+0x" +
Twine::utohexstr(dataOff + errOff) + "): " + msg);
}
/*
* Create a pair of relocs to write the value of:
* `b - (offset + a)` if Invert == false
* `(a + offset) - b` if Invert == true
*/
template <bool Invert = false>
static void createSubtraction(PointerUnion<Symbol *, InputSection *> a,
PointerUnion<Symbol *, InputSection *> b,
uint64_t off, uint8_t length,
SmallVectorImpl<Reloc> *newRelocs) {
auto subtrahend = a;
auto minuend = b;
if (Invert)
std::swap(subtrahend, minuend);
assert(subtrahend.is<Symbol *>());
Reloc subtrahendReloc(target->subtractorRelocType, /*pcrel=*/false, length,
off, /*addend=*/0, subtrahend);
Reloc minuendReloc(target->unsignedRelocType, /*pcrel=*/false, length, off,
(Invert ? 1 : -1) * off, minuend);
newRelocs->push_back(subtrahendReloc);
newRelocs->push_back(minuendReloc);
}
void EhRelocator::makePcRel(uint64_t off,
PointerUnion<Symbol *, InputSection *> target,
uint8_t length) {
createSubtraction(isec->symbols[0], target, off, length, &newRelocs);
}
void EhRelocator::makeNegativePcRel(
uint64_t off, PointerUnion<Symbol *, InputSection *> target,
uint8_t length) {
createSubtraction</*Invert=*/true>(isec, target, off, length, &newRelocs);
}
void EhRelocator::commit() {
isec->relocs.insert(isec->relocs.end(), newRelocs.begin(), newRelocs.end());
}
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