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A little elf refactoring, separate out header loading

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This commit is contained in:
Jeremy Rifkin 2025-01-24 20:16:46 -06:00
parent d063784abc
commit 485d9a6f21
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GPG Key ID: 19AA8270105E8EB4
2 changed files with 64 additions and 29 deletions
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80
src/binary/elf.cpp
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@ -54,10 +54,35 @@ namespace detail {
Result<std::uintptr_t, internal_error> elf::get_module_image_base() {
// get image base
auto impl = [this]<std::size_t Bits>() -> Result<std::uintptr_t, internal_error> {
static_assert(Bits == 32 || Bits == 64, "Unexpected Bits argument");
using PHeader = typename std::conditional<Bits == 32, Elf32_Phdr, Elf64_Phdr>::type;
auto header = get_header_info();
if(header.is_error()) {
return std::move(header).unwrap_error();
}
const auto& header_info = header.unwrap_value();
// PT_PHDR will occur at most once
// Should be somewhat reliable https://stackoverflow.com/q/61568612/15675011
// It should occur at the beginning but may as well loop just in case
for(unsigned i = 0; i < header_info.e_phnum; i++) {
auto loaded_ph = load_bytes<PHeader>(file, header_info.e_phoff + header_info.e_phentsize * i);
if(loaded_ph.is_error()) {
return std::move(loaded_ph).unwrap_error();
}
const PHeader& program_header = loaded_ph.unwrap_value();
if(byteswap_if_needed(program_header.p_type, is_little_endian) == PT_PHDR) {
return byteswap_if_needed(program_header.p_vaddr, is_little_endian) -
byteswap_if_needed(program_header.p_offset, is_little_endian);
}
}
// Apparently some objects like shared objects can end up missing this header. 0 as a base seems correct.
return 0;
};
if(is_64) {
return get_module_image_base_from_program_table<64>();
return impl.operator()<64>();
} else {
return get_module_image_base_from_program_table<32>();
return impl.operator()<32>();
}
}
@ -70,35 +95,36 @@ namespace detail {
}
}
template<std::size_t Bits>
Result<std::uintptr_t, internal_error> elf::get_module_image_base_from_program_table() {
static_assert(Bits == 32 || Bits == 64, "Unexpected Bits argument");
using Header = typename std::conditional<Bits == 32, Elf32_Ehdr, Elf64_Ehdr>::type;
using PHeader = typename std::conditional<Bits == 32, Elf32_Phdr, Elf64_Phdr>::type;
auto loaded_header = load_bytes<Header>(file, 0);
if(loaded_header.is_error()) {
return std::move(loaded_header).unwrap_error();
Result<elf::header_info, internal_error> elf::get_header_info() {
if(header) {
return header.unwrap();
}
const Header& file_header = loaded_header.unwrap_value();
if(file_header.e_ehsize != sizeof(Header)) {
return internal_error("ELF file header size mismatch" + object_path);
}
// PT_PHDR will occur at most once
// Should be somewhat reliable https://stackoverflow.com/q/61568612/15675011
// It should occur at the beginning but may as well loop just in case
for(int i = 0; i < file_header.e_phnum; i++) {
auto loaded_ph = load_bytes<PHeader>(file, file_header.e_phoff + file_header.e_phentsize * i);
if(loaded_ph.is_error()) {
return std::move(loaded_ph).unwrap_error();
auto impl = [this]<std::size_t Bits>() -> Result<header_info, internal_error> {
static_assert(Bits == 32 || Bits == 64, "Unexpected Bits argument");
using Header = typename std::conditional<Bits == 32, Elf32_Ehdr, Elf64_Ehdr>::type;
auto loaded_header = load_bytes<Header>(file, 0);
if(loaded_header.is_error()) {
return std::move(loaded_header).unwrap_error();
}
const PHeader& program_header = loaded_ph.unwrap_value();
if(byteswap_if_needed(program_header.p_type, is_little_endian) == PT_PHDR) {
return byteswap_if_needed(program_header.p_vaddr, is_little_endian) -
byteswap_if_needed(program_header.p_offset, is_little_endian);
const Header& file_header = loaded_header.unwrap_value();
if(file_header.e_ehsize != sizeof(Header)) {
return internal_error("ELF file header size mismatch" + object_path);
}
header_info info;
info.e_phoff = file_header.e_phoff;
info.e_phnum = file_header.e_phnum;
info.e_phentsize = file_header.e_phentsize;
info.e_shoff = file_header.e_shoff;
info.e_shnum = file_header.e_shnum;
info.e_shentsize = file_header.e_shentsize;
header = info;
return header.unwrap();
};
if(is_64) {
return impl.operator()<64>();
} else {
return impl.operator()<32>();
}
// Apparently some objects like shared objects can end up missing this header. 0 as a base seems correct.
return 0;
}
}
}

13
src/binary/elf.hpp
View File

@ -17,6 +17,16 @@ namespace detail {
bool is_little_endian;
bool is_64;
struct header_info {
uint64_t e_phoff;
uint32_t e_phnum;
uint32_t e_phentsize;
uint64_t e_shoff;
uint32_t e_shnum;
uint32_t e_shentsize;
};
optional<header_info> header;
elf(file_wrapper file, const std::string& object_path, bool is_little_endian, bool is_64);
public:
@ -28,8 +38,7 @@ namespace detail {
template<typename T, typename std::enable_if<std::is_integral<T>::value, int>::type = 0>
T byteswap_if_needed(T value, bool elf_is_little);
template<std::size_t Bits>
Result<std::uintptr_t, internal_error> get_module_image_base_from_program_table();
Result<header_info, internal_error> get_header_info();
};
}
}