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object_file.cc
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object_file.cc
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#include "mold.h"
#include <cstring>
#include <fcntl.h>
#include <regex>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
MemoryMappedFile *MemoryMappedFile::open(std::string path) {
struct stat st;
if (stat(path.c_str(), &st) == -1)
return nullptr;
u64 mtime = (u64)st.st_mtim.tv_sec * 1000000000 + st.st_mtim.tv_nsec;
return new MemoryMappedFile(path, nullptr, st.st_size, mtime);
}
MemoryMappedFile *MemoryMappedFile::must_open(std::string path) {
if (MemoryMappedFile *mb = MemoryMappedFile::open(path))
return mb;
Fatal() << "cannot open " << path;
}
u8 *MemoryMappedFile::data() {
if (data_)
return data_;
std::lock_guard lock(mu);
if (data_)
return data_;
i64 fd = ::open(name.c_str(), O_RDONLY);
if (fd == -1)
Fatal() << name << ": cannot open: " << strerror(errno);
data_ = (u8 *)mmap(nullptr, size_, PROT_READ, MAP_PRIVATE, fd, 0);
if (data_ == MAP_FAILED)
Fatal() << name << ": mmap failed: " << strerror(errno);
close(fd);
return data_;
}
MemoryMappedFile *MemoryMappedFile::slice(std::string name, u64 start, u64 size) {
MemoryMappedFile *mb = new MemoryMappedFile(name, data_ + start, size);
mb->parent = this;
return mb;
}
InputFile::InputFile(MemoryMappedFile *mb) : mb(mb), name(mb->name) {
if (mb->size() < sizeof(ElfEhdr))
Fatal() << *this << ": file too small";
if (memcmp(mb->data(), "\177ELF", 4))
Fatal() << *this << ": not an ELF file";
ElfEhdr &ehdr = *(ElfEhdr *)mb->data();
is_dso = (ehdr.e_type == ET_DYN);
u8 *sh_begin = mb->data() + ehdr.e_shoff;
u8 *sh_end = sh_begin + ehdr.e_shnum * sizeof(ElfShdr);
if (mb->data() + mb->size() < sh_end)
Fatal() << *this << ": e_shoff or e_shnum corrupted: "
<< mb->size() << " " << ehdr.e_shnum;
elf_sections = {(ElfShdr *)sh_begin, (ElfShdr *)sh_end};
shstrtab = get_string(ehdr.e_shstrndx);
}
std::string_view InputFile::get_string(const ElfShdr &shdr) {
u8 *begin = mb->data() + shdr.sh_offset;
u8 *end = begin + shdr.sh_size;
if (mb->data() + mb->size() < end)
Fatal() << *this << ": shdr corrupted";
return {(char *)begin, (char *)end};
}
std::string_view InputFile::get_string(i64 idx) {
if (elf_sections.size() <= idx)
Fatal() << *this << ": invalid section index";
return get_string(elf_sections[idx]);
}
template<typename T>
std::span<T> InputFile::get_data(const ElfShdr &shdr) {
std::string_view view = get_string(shdr);
if (view.size() % sizeof(T))
Fatal() << *this << ": corrupted section";
return {(T *)view.data(), view.size() / sizeof(T)};
}
template<typename T>
std::span<T> InputFile::get_data(i64 idx) {
if (elf_sections.size() <= idx)
Fatal() << *this << ": invalid section index";
return get_data<T>(elf_sections[idx]);
}
ElfShdr *InputFile::find_section(i64 type) {
for (ElfShdr &sec : elf_sections)
if (sec.sh_type == type)
return &sec;
return nullptr;
}
ObjectFile::ObjectFile(MemoryMappedFile *mb, std::string archive_name,
bool is_in_lib)
: InputFile(mb), archive_name(archive_name), is_in_lib(is_in_lib) {
is_alive = !is_in_lib;
}
void ObjectFile::initialize_sections() {
// Read sections
for (i64 i = 0; i < elf_sections.size(); i++) {
const ElfShdr &shdr = elf_sections[i];
if ((shdr.sh_flags & SHF_EXCLUDE) && !(shdr.sh_flags & SHF_ALLOC))
continue;
switch (shdr.sh_type) {
case SHT_GROUP: {
// Get the signature of this section group.
if (shdr.sh_info >= elf_syms.size())
Fatal() << *this << ": invalid symbol index";
const ElfSym &sym = elf_syms[shdr.sh_info];
std::string_view signature = symbol_strtab.data() + sym.st_name;
// Get comdat group members.
std::span<u32> entries = get_data<u32>(shdr);
if (entries.empty())
Fatal() << *this << ": empty SHT_GROUP";
if (entries[0] == 0)
continue;
if (entries[0] != GRP_COMDAT)
Fatal() << *this << ": unsupported SHT_GROUP format";
static ConcurrentMap<ComdatGroup> map;
ComdatGroup *group = map.insert(signature, ComdatGroup());
comdat_groups.push_back({group, entries});
static Counter counter("comdats");
counter++;
break;
}
case SHT_SYMTAB_SHNDX:
Fatal() << *this << ": SHT_SYMTAB_SHNDX section is not supported";
break;
case SHT_SYMTAB:
case SHT_STRTAB:
case SHT_REL:
case SHT_RELA:
case SHT_NULL:
break;
default: {
static Counter counter("regular_sections");
counter++;
std::string_view name = shstrtab.data() + shdr.sh_name;
this->sections[i] = new InputSection(this, shdr, name, i);
break;
}
}
}
// Attach relocation sections to their target sections.
for (const ElfShdr &shdr : elf_sections) {
if (shdr.sh_type != SHT_RELA)
continue;
if (shdr.sh_info >= sections.size())
Fatal() << *this << ": invalid relocated section index: "
<< (u32)shdr.sh_info;
if (InputSection *target = sections[shdr.sh_info]) {
target->rels = get_data<ElfRela>(shdr);
target->has_fragments.resize(target->rels.size());
if (target->shdr.sh_flags & SHF_ALLOC)
target->rel_types.resize(target->rels.size());
}
}
// Set is_comdat_member bits.
for (auto &pair : comdat_groups) {
std::span<u32> entries = pair.second;
for (i64 i : entries)
if (this->sections[i])
this->sections[i]->is_comdat_member = true;
}
}
void ObjectFile::initialize_ehframe_sections() {
for (i64 i = 0; i < sections.size(); i++) {
InputSection *isec = sections[i];
if (isec && isec->name == ".eh_frame") {
read_ehframe(*isec);
isec->is_ehframe = true;
sections[i] = nullptr;
}
}
}
// .eh_frame contains data records explaining how to handle exceptions.
// When an exception is thrown, the runtime searches a record from
// .eh_frame with the current program counter as a key. A record that
// covers the current PC explains how to find a handler and how to
// transfer the control ot it.
//
// Unlike the most other sections, linker has to parse .eh_frame contents
// because of the following reasons:
//
// - There's usually only one .eh_frame section for each object file,
// which explains how to handle exceptions for all functions in the same
// object. If we just copy them, the resulting .eh_frame section will
// contain lots of records for dead sections (i.e. de-duplicated inline
// functions). We want to copy only records for live functions.
//
// - .eh_frame contains two types of records: CIE and FDE. There's usually
// only one CIE at beginning of .eh_frame section followed by FDEs.
// Compiler usually emits the identical CIE record for all object files.
// We want to merge identical CIEs in an output .eh_frame section to
// reduce the section size.
//
// - Scanning a .eh_frame section to find a record is an O(n) operation
// where n is the number of records in the section. To reduce it to
// O(log n), linker creates a .eh_frame_hdr section. The section
// contains a sorted list of [an address in .text, an FDE address whose
// coverage starts at the .text address] to make binary search doable.
// In order to create .eh_frame_hdr, linker has to read .eh_frame.
//
// This function parses an input .eh_frame section.
void ObjectFile::read_ehframe(InputSection &isec) {
std::span<ElfRela> rels = isec.rels;
std::string_view data = get_string(isec.shdr);
const char *begin = data.data();
if (data.empty()) {
cies.push_back(CieRecord{data});
return;
}
std::unordered_map<i64, i64> offset_to_cie;
i64 cur_cie = -1;
i64 cur_cie_offset = -1;
for (ElfRela rel : rels)
if (rel.r_type != R_X86_64_32 && rel.r_type != R_X86_64_PC32)
Fatal() << isec << ": unsupported relocation type: " << rel.r_type;
while (!data.empty()) {
i64 size = *(u32 *)data.data();
if (size == 0) {
if (data.size() != 4)
Fatal() << isec << ": garbage at end of section";
cies.push_back(CieRecord{data});
return;
}
i64 begin_offset = data.data() - begin;
i64 end_offset = begin_offset + size + 4;
if (!rels.empty() && rels[0].r_offset < begin_offset)
Fatal() << isec << ": unsupported relocation order";
std::string_view contents = data.substr(0, size + 4);
data = data.substr(size + 4);
i64 id = *(u32 *)(contents.data() + 4);
std::vector<EhReloc> eh_rels;
while (!rels.empty() && rels[0].r_offset < end_offset) {
if (id && first_global <= rels[0].r_sym)
Fatal() << isec << ": FDE with non-local relocations is not supported";
Symbol &sym = *symbols[rels[0].r_sym];
eh_rels.push_back(EhReloc{sym, rels[0].r_type,
(u32)(rels[0].r_offset - begin_offset),
rels[0].r_addend});
rels = rels.subspan(1);
}
if (id == 0) {
// CIE
cur_cie = cies.size();
offset_to_cie[begin_offset] = cies.size();
cies.push_back(CieRecord{contents, std::move(eh_rels)});
} else {
// FDE
i64 cie_offset = begin_offset + 4 - id;
if (cie_offset != cur_cie_offset) {
auto it = offset_to_cie.find(cie_offset);
if (it == offset_to_cie.end())
Fatal() << isec << ": bad FDE pointer";
cur_cie = it->second;
cur_cie_offset = cie_offset;
}
if (eh_rels.empty())
Fatal() << isec << ": FDE has no relocations";
if (eh_rels[0].offset != 8)
Fatal() << isec << ": FDE's first relocation should have offset 8";
FdeRecord fde(contents, std::move(eh_rels), cur_cie);
cies[cur_cie].fdes.push_back(std::move(fde));
}
}
for (CieRecord &cie : cies) {
std::span<FdeRecord> fdes = cie.fdes;
while (!fdes.empty()) {
InputSection *isec = fdes[0].rels[0].sym.input_section;
i64 i = 1;
while (i < fdes.size() && isec == fdes[i].rels[0].sym.input_section)
i++;
isec->fdes = fdes.subspan(0, i);
fdes = fdes.subspan(i);
}
}
}
static bool should_write_symtab(Symbol &sym) {
if (config.discard_all || config.strip_all)
return false;
if (sym.esym->st_type == STT_SECTION)
return false;
// Local symbols are discarded if --discard-local is given or they
// are not in a mergeable section. I *believe* we exclude symbols in
// mergeable sections because (1) they are too many and (2) they are
// merged, so their origins shouldn't matter, but I dont' really
// know the rationale. Anyway, this is the behavior of the
// traditional linkers.
if (sym.name.starts_with(".L")) {
if (config.discard_locals)
return false;
if (InputSection *isec = sym.input_section)
if (isec->shdr.sh_flags & SHF_MERGE)
return false;
}
return true;
}
void ObjectFile::initialize_symbols() {
if (!symtab_sec)
return;
static Counter counter("all_syms");
counter += elf_syms.size();
// Initialize local symbols
Symbol *locals = new Symbol[first_global];
for (i64 i = 1; i < first_global; i++) {
const ElfSym &esym = elf_syms[i];
Symbol &sym = locals[i];
sym.name = symbol_strtab.data() + esym.st_name;
sym.file = this;
sym.st_type = esym.st_type;
sym.value = esym.st_value;
sym.esym = &esym;
if (!esym.is_abs()) {
if (esym.is_common())
Fatal() << *this << ": common local symbol?";
sym.input_section = sections[esym.st_shndx];
}
if (should_write_symtab(sym)) {
sym.write_symtab = true;
strtab_size += sym.name.size() + 1;
num_local_symtab++;
}
}
symbols.resize(elf_syms.size());
sym_fragments.resize(elf_syms.size() - first_global);
for (i64 i = 0; i < first_global; i++)
symbols[i] = &locals[i];
// Initialize global symbols
for (i64 i = first_global; i < elf_syms.size(); i++) {
const ElfSym &esym = elf_syms[i];
std::string_view name = symbol_strtab.data() + esym.st_name;
i64 pos = name.find('@');
if (pos != std::string_view::npos)
name = name.substr(0, pos);
symbols[i] = Symbol::intern(name);
if (esym.is_common())
has_common_symbol = true;
}
}
void ObjectFile::initialize_mergeable_sections() {
mergeable_sections.resize(sections.size());
for (i64 i = 0; i < sections.size(); i++) {
if (InputSection *isec = sections[i]) {
if (isec->shdr.sh_flags & SHF_MERGE) {
mergeable_sections[i] = new MergeableSection(isec);
sections[i] = nullptr;
}
}
}
// Initialize rel_fragments
for (InputSection *isec : sections) {
if (!isec || isec->rels.empty())
continue;
for (i64 i = 0; i < isec->rels.size(); i++) {
const ElfRela &rel = isec->rels[i];
const ElfSym &esym = elf_syms[rel.r_sym];
if (esym.st_type != STT_SECTION)
continue;
MergeableSection *m = mergeable_sections[esym.st_shndx];
if (!m)
continue;
i64 offset = esym.st_value + rel.r_addend;
std::span<u32> offsets = m->frag_offsets;
auto it = std::upper_bound(offsets.begin(), offsets.end(), offset);
if (it == offsets.begin())
Fatal() << *this << ": bad relocation at " << rel.r_sym;
i64 idx = it - 1 - offsets.begin();
SectionFragmentRef ref{m->fragments[idx], (i32)(offset - offsets[idx])};
isec->rel_fragments.push_back(ref);
isec->has_fragments[i] = true;
}
}
// Initialize sym_fragments
for (i64 i = 0; i < elf_syms.size(); i++) {
const ElfSym &esym = elf_syms[i];
if (esym.is_abs() || esym.is_common())
continue;
MergeableSection *m = mergeable_sections[esym.st_shndx];
if (!m)
continue;
std::span<u32> offsets = m->frag_offsets;
auto it = std::upper_bound(offsets.begin(), offsets.end(), esym.st_value);
if (it == offsets.begin())
Fatal() << *this << ": bad symbol value: " << esym.st_value;
i64 idx = it - 1 - offsets.begin();
if (i < first_global) {
symbols[i]->frag = m->fragments[idx];
symbols[i]->value = esym.st_value - offsets[idx];
} else {
sym_fragments[i - first_global].frag = m->fragments[idx];
sym_fragments[i - first_global].addend = esym.st_value - offsets[idx];
}
}
erase(mergeable_sections, [](MergeableSection *m) { return !m; });
}
void ObjectFile::parse() {
sections.resize(elf_sections.size());
symtab_sec = find_section(SHT_SYMTAB);
if (symtab_sec) {
first_global = symtab_sec->sh_info;
elf_syms = get_data<ElfSym>(*symtab_sec);
symbol_strtab = get_string(symtab_sec->sh_link);
}
initialize_sections();
initialize_symbols();
initialize_mergeable_sections();
initialize_ehframe_sections();
}
// Symbols with higher priorities overwrites symbols with lower priorities.
// Here is the list of priorities, from the highest to the lowest.
//
// 1. Strong defined symbol
// 2. Weak defined symbol
// 3. Defined symbol in an archive member
// 4. Unclaimed (nonexistent) symbol
//
// Ties are broken by file priority.
static u64 get_rank(InputFile *file, const ElfSym &esym, InputSection *isec) {
if (isec && isec->is_comdat_member)
return file->priority;
if (esym.is_undef()) {
assert(esym.st_bind == STB_WEAK);
return ((u64)2 << 32) + file->priority;
}
if (esym.st_bind == STB_WEAK)
return ((u64)1 << 32) + file->priority;
return file->priority;
}
static u64 get_rank(const Symbol &sym) {
if (!sym.file)
return (u64)4 << 32;
if (sym.is_placeholder)
return ((u64)3 << 32) + sym.file->priority;
return get_rank(sym.file, *sym.esym, sym.input_section);
}
void ObjectFile::maybe_override_symbol(Symbol &sym, i64 symidx) {
InputSection *isec = nullptr;
const ElfSym &esym = elf_syms[symidx];
if (!esym.is_abs() && !esym.is_common())
isec = sections[esym.st_shndx];
std::lock_guard lock(sym.mu);
u64 new_rank = get_rank(this, esym, isec);
u64 existing_rank = get_rank(sym);
if (new_rank < existing_rank) {
sym.file = this;
sym.input_section = isec;
if (SectionFragmentRef &ref = sym_fragments[symidx - first_global]; ref.frag) {
sym.frag = ref.frag;
sym.value = ref.addend;
} else {
sym.value = esym.st_value;
}
sym.ver_idx = 0;
sym.st_type = esym.st_type;
sym.esym = &esym;
sym.is_placeholder = false;
if (sym.traced) {
bool is_weak = (esym.st_bind == STB_WEAK);
SyncOut() << "trace: " << *sym.file
<< (is_weak ? ": weak definition of " : ": definition of ")
<< sym.name;
}
}
}
void ObjectFile::resolve_symbols() {
for (i64 i = first_global; i < symbols.size(); i++) {
const ElfSym &esym = elf_syms[i];
if (!esym.is_defined())
continue;
Symbol &sym = *symbols[i];
if (is_in_lib) {
std::lock_guard lock(sym.mu);
bool is_new = !sym.file;
bool tie_but_higher_priority =
sym.is_placeholder && this->priority < sym.file->priority;
if (is_new || tie_but_higher_priority) {
sym.file = this;
sym.is_placeholder = true;
if (sym.traced)
SyncOut() << "trace: " << *sym.file
<< ": lazy definition of " << sym.name;
}
} else {
maybe_override_symbol(sym, i);
}
}
}
void ObjectFile::mark_live_objects(std::function<void(ObjectFile *)> feeder) {
assert(is_alive);
for (i64 i = first_global; i < symbols.size(); i++) {
const ElfSym &esym = elf_syms[i];
Symbol &sym = *symbols[i];
if (esym.is_defined()) {
if (is_in_lib)
maybe_override_symbol(sym, i);
continue;
}
if (sym.traced)
SyncOut() << "trace: " << *this << ": reference to " << sym.name;
if (esym.st_bind != STB_WEAK && sym.file && !sym.file->is_alive.exchange(true)) {
if (!sym.file->is_dso)
feeder((ObjectFile *)sym.file);
if (sym.traced)
SyncOut() << "trace: " << *this << " keeps " << *sym.file
<< " for " << sym.name;
}
}
}
void ObjectFile::handle_undefined_weak_symbols() {
for (i64 i = first_global; i < symbols.size(); i++) {
const ElfSym &esym = elf_syms[i];
if (esym.is_undef() && esym.st_bind == STB_WEAK) {
Symbol &sym = *symbols[i];
std::lock_guard lock(sym.mu);
bool is_new = !sym.file || sym.is_placeholder;
bool tie_but_higher_priority =
!is_new && sym.is_undef_weak() && this->priority < sym.file->priority;
if (is_new || tie_but_higher_priority) {
sym.file = this;
sym.input_section = nullptr;
sym.value = 0;
sym.esym = &esym;
sym.is_placeholder = false;
if (sym.traced)
SyncOut() << "trace: " << *this << ": unresolved weak symbol "
<< sym.name;
}
}
}
}
void ObjectFile::resolve_comdat_groups() {
for (auto &pair : comdat_groups) {
ComdatGroup *group = pair.first;
ObjectFile *cur = group->owner;
while (!cur || cur->priority > this->priority)
if (group->owner.compare_exchange_weak(cur, this))
break;
}
}
void ObjectFile::eliminate_duplicate_comdat_groups() {
for (auto &pair : comdat_groups) {
ComdatGroup *group = pair.first;
if (group->owner == this)
continue;
std::span<u32> entries = pair.second;
for (i64 i : entries)
if (sections[i])
sections[i]->kill();
static Counter counter("removed_comdat_mem");
counter += entries.size();
}
}
void ObjectFile::claim_unresolved_symbols() {
if (!is_alive)
return;
for (i64 i = first_global; i < symbols.size(); i++) {
const ElfSym &esym = elf_syms[i];
Symbol &sym = *symbols[i];
std::lock_guard lock(sym.mu);
if (esym.is_undef() && (!sym.esym || sym.esym->is_undef())) {
if (sym.file && sym.file->priority < this->priority)
continue;
sym.file = this;
sym.esym = &esym;
}
}
}
void ObjectFile::scan_relocations() {
// Scan relocations against seciton contents
for (InputSection *isec : sections)
if (isec)
isec->scan_relocations();
// Scan relocations against exception frames
for (CieRecord &cie : cies) {
for (EhReloc &rel : cie.rels) {
if (!rel.sym.is_imported())
continue;
if (rel.sym.st_type != STT_FUNC)
Fatal() << *this << ": " << rel.sym.name
<< ": .eh_frame CIE record with an external data reference"
<< " is not supported";
rel.sym.flags |= NEEDS_PLT;
}
}
}
void ObjectFile::convert_common_symbols() {
if (!has_common_symbol)
return;
static OutputSection *bss =
OutputSection::get_instance(".bss", SHT_NOBITS, SHF_WRITE | SHF_ALLOC);
for (i64 i = first_global; i < elf_syms.size(); i++) {
if (!elf_syms[i].is_common())
continue;
Symbol *sym = symbols[i];
if (sym->file != this)
continue;
auto *shdr = new ElfShdr;
memset(shdr, 0, sizeof(*shdr));
shdr->sh_flags = SHF_ALLOC;
shdr->sh_type = SHT_NOBITS;
shdr->sh_size = elf_syms[i].st_size;
shdr->sh_addralign = 1;
auto *isec = new InputSection(this, *shdr, ".bss", sections.size());
isec->output_section = bss;
sections.push_back(isec);
sym->input_section = isec;
sym->value = 0;
}
}
static bool should_write_global_symtab(Symbol &sym) {
return sym.esym->st_type != STT_SECTION && sym.is_alive();
}
void ObjectFile::compute_symtab() {
if (config.strip_all)
return;
if (config.gc_sections && !config.discard_all) {
// Detect symbols pointing to sections discarded by -gc-sections
// to remove them from symtab.
for (i64 i = 1; i < first_global; i++) {
Symbol &sym = *symbols[i];
if (sym.write_symtab && !sym.is_alive()) {
strtab_size -= sym.name.size() + 1;
num_local_symtab--;
sym.write_symtab = false;
}
}
}
// Compute the size of global symbols.
for (i64 i = first_global; i < elf_syms.size(); i++) {
Symbol &sym = *symbols[i];
if (sym.file == this && should_write_global_symtab(sym)) {
strtab_size += sym.name.size() + 1;
num_global_symtab++;
}
}
}
void ObjectFile::write_symtab() {
u8 *symtab_base = out::buf + out::symtab->shdr.sh_offset;
u8 *strtab_base = out::buf + out::strtab->shdr.sh_offset;
i64 symtab_off;
i64 strtab_off = strtab_offset;
auto write_sym = [&](i64 i) {
Symbol &sym = *symbols[i];
ElfSym &esym = *(ElfSym *)(symtab_base + symtab_off);
symtab_off += sizeof(ElfSym);
esym = elf_syms[i];
esym.st_name = strtab_off;
if (sym.st_type == STT_TLS)
esym.st_value = sym.get_addr() - out::tls_begin;
else
esym.st_value = sym.get_addr();
if (sym.input_section)
esym.st_shndx = sym.input_section->output_section->shndx;
else if (sym.shndx)
esym.st_shndx = sym.shndx;
else
esym.st_shndx = SHN_ABS;
write_string(strtab_base + strtab_off, sym.name);
strtab_off += sym.name.size() + 1;
};
symtab_off = local_symtab_offset;
for (i64 i = 1; i < first_global; i++)
if (symbols[i]->write_symtab)
write_sym(i);
symtab_off = global_symtab_offset;
for (i64 i = first_global; i < elf_syms.size(); i++)
if (symbols[i]->file == this && should_write_global_symtab(*symbols[i]))
write_sym(i);
}
bool is_c_identifier(std::string_view name) {
static std::regex re("[a-zA-Z_][a-zA-Z0-9_]*");
return std::regex_match(name.begin(), name.end(), re);
}
ObjectFile::ObjectFile() {
// Create linker-synthesized symbols.
auto *esyms = new std::vector<ElfSym>(1);
symbols.push_back(new Symbol);
first_global = 1;
is_alive = true;
priority = 1;
auto add = [&](std::string_view name, u8 visibility = STV_DEFAULT) {
ElfSym esym = {};
esym.st_type = STT_NOTYPE;
esym.st_shndx = SHN_ABS;
esym.st_bind = STB_GLOBAL;
esym.st_visibility = visibility;
esyms->push_back(esym);
Symbol *sym = Symbol::intern(name);
symbols.push_back(sym);
return sym;
};
out::__ehdr_start = add("__ehdr_start", STV_HIDDEN);
out::__rela_iplt_start = add("__rela_iplt_start", STV_HIDDEN);
out::__rela_iplt_end = add("__rela_iplt_end", STV_HIDDEN);
out::__init_array_start = add("__init_array_start", STV_HIDDEN);
out::__init_array_end = add("__init_array_end", STV_HIDDEN);
out::__fini_array_start = add("__fini_array_start", STV_HIDDEN);
out::__fini_array_end = add("__fini_array_end", STV_HIDDEN);
out::__preinit_array_start = add("__preinit_array_start", STV_HIDDEN);
out::__preinit_array_end = add("__preinit_array_end", STV_HIDDEN);
out::_DYNAMIC = add("_DYNAMIC", STV_HIDDEN);
out::_GLOBAL_OFFSET_TABLE_ = add("_GLOBAL_OFFSET_TABLE_", STV_HIDDEN);
out::__bss_start = add("__bss_start", STV_HIDDEN);
out::_end = add("_end", STV_HIDDEN);
out::_etext = add("_etext", STV_HIDDEN);
out::_edata = add("_edata", STV_HIDDEN);
if (config.eh_frame_hdr)
out::__GNU_EH_FRAME_HDR = add("__GNU_EH_FRAME_HDR", STV_HIDDEN);
for (OutputChunk *chunk : out::chunks) {
if (!is_c_identifier(chunk->name))
continue;
auto *start = new std::string("__start_" + std::string(chunk->name));
auto *stop = new std::string("__stop_" + std::string(chunk->name));
add(*start, STV_HIDDEN);
add(*stop, STV_HIDDEN);
}
elf_syms = *esyms;
sym_fragments.resize(elf_syms.size() - first_global);
}
std::ostream &operator<<(std::ostream &out, const InputFile &file) {
if (file.is_dso) {
out << file.name;
return out;
}
ObjectFile *obj = (ObjectFile *)&file;
if (obj->archive_name == "")
out << obj->name;
else
out << obj->archive_name << "(" << obj->name + ")";
return out;
}
std::string_view SharedFile::get_soname() {
if (ElfShdr *sec = find_section(SHT_DYNAMIC))
for (ElfDyn &dyn : get_data<ElfDyn>(*sec))
if (dyn.d_tag == DT_SONAME)
return symbol_strtab.data() + dyn.d_val;
return name;
}
void SharedFile::parse() {
symtab_sec = find_section(SHT_DYNSYM);
if (!symtab_sec)
return;
symbol_strtab = get_string(symtab_sec->sh_link);
soname = get_soname();
version_strings = read_verdef();
// Read a symbol table.
i64 first_global = symtab_sec->sh_info;
std::span<ElfSym> esyms = get_data<ElfSym>(*symtab_sec);
std::span<u16> vers;
if (ElfShdr *sec = find_section(SHT_GNU_VERSYM))
vers = get_data<u16>(*sec);
for (i64 i = first_global; i < esyms.size(); i++) {
if (!vers.empty() && (vers[i] >> 15) == 1)
continue;
std::string_view name = symbol_strtab.data() + esyms[i].st_name;
Symbol *sym = Symbol::intern(name);
if (esyms[i].is_defined()) {
elf_syms.push_back(&esyms[i]);
versyms.push_back(vers.empty() ? 1 : vers[i]);
symbols.push_back(sym);
} else {
undefs.push_back(sym);
}
}
static Counter counter("dso_syms");
counter += elf_syms.size();
}
std::vector<std::string_view> SharedFile::read_verdef() {
ElfShdr *verdef_sec = find_section(SHT_GNU_VERDEF);
if (!verdef_sec)
return {};
std::string_view verdef = get_string(*verdef_sec);
std::string_view strtab = get_string(verdef_sec->sh_link);
std::vector<std::string_view> ret(2);
auto *ver = (ElfVerdef *)verdef.data();
for (;;) {
if (ret.size() <= ver->vd_ndx)
ret.resize(ver->vd_ndx + 1);
ElfVerdaux *aux = (ElfVerdaux *)((u8 *)ver + ver->vd_aux);
ret[ver->vd_ndx] = strtab.data() + aux->vda_name;
if (!ver->vd_next)
break;
ver = (ElfVerdef *)((u8 *)ver + ver->vd_next);
}
return ret;
}
void SharedFile::resolve_symbols() {
for (i64 i = 0; i < symbols.size(); i++) {
Symbol &sym = *symbols[i];
const ElfSym &esym = *elf_syms[i];
std::lock_guard lock(sym.mu);
u64 new_rank = get_rank(this, esym, nullptr);
u64 existing_rank = get_rank(sym);
if (new_rank < existing_rank) {
sym.file = this;
sym.input_section = nullptr;
sym.frag = nullptr;
sym.value = esym.st_value;
sym.ver_idx = versyms[i];
sym.st_type = (esym.st_type == STT_GNU_IFUNC) ? STT_FUNC : esym.st_type;
sym.esym = &esym;
sym.is_placeholder = false;
if (sym.traced) {
bool is_weak = (esym.st_bind == STB_WEAK);
SyncOut() << "trace: " << *sym.file
<< (is_weak ? ": weak definition of " : ": definition of ")
<< sym.name;
}
}
}
}
std::vector<Symbol *> SharedFile::find_aliases(Symbol *sym) {
assert(sym->file == this);
std::vector<Symbol *> vec;
for (Symbol *sym2 : symbols)
if (sym != sym2 && sym->value == sym2->value)
vec.push_back(sym2);
return vec;
}