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elf_rela.cc
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elf_rela.cc
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/*
* Copyright 2021 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Author: Yonghyun Hwang <[email protected]>
*/
#include "elf_rela.h"
#include <limits>
#include <string_view>
#include <system_error>
#include "elf_error.h"
#include "llvm/Support/raw_ostream.h"
namespace
{
void throw_gelf_error()
{
throw std::error_code{ static_cast<ElfErrorCode>(elf_errno()) };
}
bool HasAllocFlag(Elf *elf, size_t sec_id)
{
Elf_Scn *scn = elf_getscn(elf, sec_id);
if (scn == nullptr) {
throw_gelf_error();
}
GElf_Shdr sec_header{};
if (!gelf_getshdr(scn, &sec_header)) {
throw_gelf_error();
}
return sec_header.sh_flags & SHF_ALLOC;
}
} // namespace
ElfRela::ElfRela(Elf *elf) noexcept(false) : elf_(elf), symbol_(elf_)
{
if (!GetNextRela()) {
throw std::error_code{ ElfErrorCode::NO_RELA_SECTION };
}
}
ElfRela::RelaEntry *ElfRela::Entry() noexcept(false)
{
if (gelf_getrela(rela_data_, rela_cursor_, &rela_entry_) == nullptr) {
throw_gelf_error();
}
return &rela_entry_;
}
std::string_view ElfRela::Name()
{
return symbol_.Name(GELF_R_SYM(Entry()->r_info));
}
void ElfRela::PrintCurrentEntry()
{
llvm::outs()
<< "Section: " << SectionId() << ", Symbol: " << Name() << "\n";
}
bool ElfRela::HasSectionIndex(ElfSymbol::SectionIndex idx)
{
return symbol_.HasSectionIndex(idx, GELF_R_SYM(Entry()->r_info));
}
void ElfRela::SetSectionIndex(ElfSymbol::SectionIndex idx)
{
return symbol_.SetSectionIndex(idx, GELF_R_SYM(Entry()->r_info));
}
Elf_Scn *ElfRela::GetNextRela()
{
while ((scn_ = elf_nextscn(elf_, scn_))) {
gelf_getshdr(scn_, &rela_header_);
// Section relocated by KLP RELA should have SHF_ALLOC flag because
// kernel module loader frees sections without the flag before KLP
// RELA kicks in. So, skip RELA sections for sections without the
// flag.
if (rela_header_.sh_type == SHT_RELA &&
HasAllocFlag(elf_, this->SectionId()))
break;
}
if (scn_ == nullptr) {
rela_cursor_ = std::numeric_limits<size_t>::max();
rela_data_ = nullptr;
rela_count_ = 0;
return nullptr;
}
rela_data_ = elf_getdata(scn_, nullptr);
rela_count_ = rela_header_.sh_size / rela_header_.sh_entsize;
if (rela_count_ > 0) {
// rela_cursor_ starts with 0 while terminating condition for next
// iteration is rela_cursor_ == rela_count_.
rela_count_--;
}
rela_cursor_ = 0;
return scn_;
}
bool ElfRela::Iterator::operator==(const Iterator &other) const
{
if (rela_ != other.rela_) {
return false;
}
if (rela_ == nullptr) {
return true;
}
return rela_->elf_ == other.rela_->elf_;
}
ElfRela::Iterator &ElfRela::Iterator::operator++()
{
if (rela_ == nullptr) {
return *this;
}
if (rela_->rela_cursor_ >= rela_->rela_count_) {
if (!rela_->GetNextRela()) {
rela_ = nullptr;
}
return *this;
}
rela_->rela_cursor_++;
return *this;
}