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/*
* Copyright (C) 2018 The Android Open Source Project
*
* 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
*
* http://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.
*/
#ifndef ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
#define ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
#include "base/array_ref.h"
#include "dwarf/headers.h"
#include "elf/elf_utils.h"
#include "xz_utils.h"
#include <map>
#include <string_view>
namespace art {
// Trivial ELF file reader.
//
// It is the bare minimum needed to read mini-debug-info symbols for unwinding.
// We use it to merge JIT mini-debug-infos together or to prune them after GC.
template <typename ElfTypes>
class ElfDebugReader {
public:
// Note that the input buffer might be misaligned.
typedef typename ElfTypes::Ehdr ALIGNED(1) Elf_Ehdr;
typedef typename ElfTypes::Shdr ALIGNED(1) Elf_Shdr;
typedef typename ElfTypes::Sym ALIGNED(1) Elf_Sym;
typedef typename ElfTypes::Addr ALIGNED(1) Elf_Addr;
// Call Frame Information.
struct CFI {
uint32_t length; // Length excluding the size of this field.
int32_t cie_pointer; // Offset in the section or -1 for CIE.
const uint8_t* data() const { return reinterpret_cast<const uint8_t*>(this); }
size_t size() const { return sizeof(uint32_t) + length; }
} PACKED(1);
// Common Information Entry.
struct CIE : public CFI {
} PACKED(1);
// Frame Description Entry.
struct FDE : public CFI {
Elf_Addr sym_addr;
Elf_Addr sym_size;
} PACKED(1);
explicit ElfDebugReader(ArrayRef<const uint8_t> file) : file_(file) {
header_ = Read<Elf_Ehdr>(/*offset=*/ 0);
CHECK_EQ(header_->e_ident[0], ELFMAG0);
CHECK_EQ(header_->e_ident[1], ELFMAG1);
CHECK_EQ(header_->e_ident[2], ELFMAG2);
CHECK_EQ(header_->e_ident[3], ELFMAG3);
CHECK_EQ(header_->e_ehsize, sizeof(Elf_Ehdr));
CHECK_EQ(header_->e_shentsize, sizeof(Elf_Shdr));
// Find all ELF sections.
sections_ = Read<Elf_Shdr>(header_->e_shoff, header_->e_shnum);
for (const Elf_Shdr& section : sections_) {
const char* name = Read<char>(sections_[header_->e_shstrndx].sh_offset + section.sh_name);
section_map_[std::string_view(name)] = §ion;
}
// Decompressed embedded debug symbols, if any.
const Elf_Shdr* gnu_debugdata = section_map_[".gnu_debugdata"];
if (gnu_debugdata != nullptr) {
auto compressed = Read<uint8_t>(gnu_debugdata->sh_offset, gnu_debugdata->sh_size);
XzDecompress(compressed, &decompressed_gnu_debugdata_);
gnu_debugdata_reader_.reset(new ElfDebugReader(decompressed_gnu_debugdata_));
}
}
explicit ElfDebugReader(std::vector<uint8_t>& file)
: ElfDebugReader(ArrayRef<const uint8_t>(file)) {
}
const Elf_Ehdr* GetHeader() { return header_; }
ArrayRef<Elf_Shdr> GetSections() { return sections_; }
const Elf_Shdr* GetSection(const char* name) { return section_map_[name]; }
template <typename VisitSym>
void VisitFunctionSymbols(VisitSym visit_sym) {
const Elf_Shdr* symtab = GetSection(".symtab");
const Elf_Shdr* strtab = GetSection(".strtab");
const Elf_Shdr* text = GetSection(".text");
if (symtab != nullptr && strtab != nullptr) {
CHECK_EQ(symtab->sh_entsize, sizeof(Elf_Sym));
size_t count = symtab->sh_size / sizeof(Elf_Sym);
for (const Elf_Sym& symbol : Read<Elf_Sym>(symtab->sh_offset, count)) {
if (ELF_ST_TYPE(symbol.st_info) == STT_FUNC && §ions_[symbol.st_shndx] == text) {
visit_sym(symbol, Read<char>(strtab->sh_offset + symbol.st_name));
}
}
}
if (gnu_debugdata_reader_ != nullptr) {
gnu_debugdata_reader_->VisitFunctionSymbols(visit_sym);
}
}
template <typename VisitSym>
void VisitDynamicSymbols(VisitSym visit_sym) {
const Elf_Shdr* dynsym = GetSection(".dynsym");
const Elf_Shdr* dynstr = GetSection(".dynstr");
if (dynsym != nullptr && dynstr != nullptr) {
CHECK_EQ(dynsym->sh_entsize, sizeof(Elf_Sym));
size_t count = dynsym->sh_size / sizeof(Elf_Sym);
for (const Elf_Sym& symbol : Read<Elf_Sym>(dynsym->sh_offset, count)) {
visit_sym(symbol, Read<char>(dynstr->sh_offset + symbol.st_name));
}
}
}
template <typename VisitCIE, typename VisitFDE>
void VisitDebugFrame(VisitCIE visit_cie, VisitFDE visit_fde) {
const Elf_Shdr* debug_frame = GetSection(".debug_frame");
if (debug_frame != nullptr) {
for (size_t offset = 0; offset < debug_frame->sh_size;) {
const CFI* entry = Read<CFI>(debug_frame->sh_offset + offset);
DCHECK_LE(entry->size(), debug_frame->sh_size - offset);
if (entry->cie_pointer == -1) {
visit_cie(Read<CIE>(debug_frame->sh_offset + offset));
} else {
const FDE* fde = Read<FDE>(debug_frame->sh_offset + offset);
visit_fde(fde, Read<CIE>(debug_frame->sh_offset + fde->cie_pointer));
}
offset += entry->size();
}
}
if (gnu_debugdata_reader_ != nullptr) {
gnu_debugdata_reader_->VisitDebugFrame(visit_cie, visit_fde);
}
}
private:
template<typename T>
const T* Read(size_t offset) {
DCHECK_LE(offset + sizeof(T), file_.size());
return reinterpret_cast<const T*>(file_.data() + offset);
}
template<typename T>
ArrayRef<const T> Read(size_t offset, size_t count) {
DCHECK_LE(offset + count * sizeof(T), file_.size());
return ArrayRef<const T>(Read<T>(offset), count);
}
ArrayRef<const uint8_t> const file_;
const Elf_Ehdr* header_;
ArrayRef<const Elf_Shdr> sections_;
std::unordered_map<std::string_view, const Elf_Shdr*> section_map_;
std::vector<uint8_t> decompressed_gnu_debugdata_;
std::unique_ptr<ElfDebugReader> gnu_debugdata_reader_;
DISALLOW_COPY_AND_ASSIGN(ElfDebugReader);
};
} // namespace art
#endif // ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
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