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main.cc
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#include "mold.h"
#include <functional>
#include <map>
#include <signal.h>
#include <tbb/global_control.h>
#include <tbb/parallel_do.h>
#include <tbb/parallel_for_each.h>
#include <unordered_set>
i64 BuildId::size() const {
switch (kind) {
case HEX:
return value.size();
case HASH:
return hash_size;
case UUID:
return 16;
}
unreachable();
}
static bool is_text_file(MemoryMappedFile *mb) {
return mb->size() >= 4 &&
isprint(mb->data()[0]) &&
isprint(mb->data()[1]) &&
isprint(mb->data()[2]) &&
isprint(mb->data()[3]);
}
enum class FileType { UNKNOWN, OBJ, DSO, AR, THIN_AR, TEXT };
static FileType get_file_type(MemoryMappedFile *mb) {
if (mb->size() >= 20 && memcmp(mb->data(), "\177ELF", 4) == 0) {
ElfEhdr &ehdr = *(ElfEhdr *)mb->data();
if (ehdr.e_type == ET_REL)
return FileType::OBJ;
if (ehdr.e_type == ET_DYN)
return FileType::DSO;
return FileType::UNKNOWN;
}
if (mb->size() >= 8 && memcmp(mb->data(), "!<arch>\n", 8) == 0)
return FileType::AR;
if (mb->size() >= 8 && memcmp(mb->data(), "!<thin>\n", 8) == 0)
return FileType::THIN_AR;
if (is_text_file(mb))
return FileType::TEXT;
return FileType::UNKNOWN;
}
static ObjectFile *new_object_file(MemoryMappedFile *mb,
std::string archive_name,
ReadContext &ctx) {
static Counter count("parsed_objs");
count++;
bool in_lib = (!archive_name.empty() && !ctx.whole_archive);
ObjectFile *file = new ObjectFile(mb, archive_name, in_lib);
ctx.tg.run([=]() { file->parse(); });
if (config.trace)
SyncOut() << "trace: " << *file;
return file;
}
static SharedFile *new_shared_file(MemoryMappedFile *mb, ReadContext &ctx) {
SharedFile *file = new SharedFile(mb, ctx.as_needed);
ctx.tg.run([=]() { file->parse(); });
if (config.trace)
SyncOut() << "trace: " << *file;
return file;
}
template <typename T>
class FileCache {
public:
void store(MemoryMappedFile *mb, T *obj) {
Key k(mb->name, mb->size(), mb->mtime);
cache[k].push_back(obj);
}
std::vector<T *> get(MemoryMappedFile *mb) {
Key k(mb->name, mb->size(), mb->mtime);
std::vector<T *> objs = cache[k];
cache[k].clear();
return objs;
}
T *get_one(MemoryMappedFile *mb) {
std::vector<T *> objs = get(mb);
return objs.empty() ? nullptr : objs[0];
}
private:
typedef std::tuple<std::string, i64, i64> Key;
std::map<Key, std::vector<T *>> cache;
};
void read_file(MemoryMappedFile *mb, ReadContext &ctx) {
if (ctx.visited.contains(mb->name))
return;
static FileCache<ObjectFile> obj_cache;
static FileCache<SharedFile> dso_cache;
if (ctx.is_preloading) {
switch (get_file_type(mb)) {
case FileType::OBJ:
obj_cache.store(mb, new_object_file(mb, "", ctx));
return;
case FileType::DSO:
dso_cache.store(mb, new_shared_file(mb, ctx));
return;
case FileType::AR:
for (MemoryMappedFile *child : read_fat_archive_members(mb))
obj_cache.store(mb, new_object_file(child, mb->name, ctx));
return;
case FileType::THIN_AR:
for (MemoryMappedFile *child : read_thin_archive_members(mb))
obj_cache.store(child, new_object_file(child, mb->name, ctx));
return;
case FileType::TEXT:
parse_linker_script(mb, ctx);
return;
}
Fatal() << mb->name << ": unknown file type";
}
switch (get_file_type(mb)) {
case FileType::OBJ:
if (ObjectFile *obj = obj_cache.get_one(mb))
out::objs.push_back(obj);
else
out::objs.push_back(new_object_file(mb, "", ctx));
return;
case FileType::DSO:
if (SharedFile *obj = dso_cache.get_one(mb))
out::dsos.push_back(obj);
else
out::dsos.push_back(new_shared_file(mb, ctx));
ctx.visited.insert(mb->name);
return;
case FileType::AR:
if (std::vector<ObjectFile *> objs = obj_cache.get(mb); !objs.empty()) {
append(out::objs, objs);
} else {
for (MemoryMappedFile *child : read_archive_members(mb))
out::objs.push_back(new_object_file(child, mb->name, ctx));
}
ctx.visited.insert(mb->name);
return;
case FileType::THIN_AR:
for (MemoryMappedFile *child : read_thin_archive_members(mb)) {
if (ObjectFile *obj = obj_cache.get_one(child))
out::objs.push_back(obj);
else
out::objs.push_back(new_object_file(child, mb->name, ctx));
}
ctx.visited.insert(mb->name);
return;
case FileType::TEXT:
parse_linker_script(mb, ctx);
return;
}
Fatal() << mb->name << ": unknown file type";
}
template <typename T>
static std::vector<std::span<T>> split(std::vector<T> &input, i64 unit) {
assert(input.size() > 0);
std::span<T> span(input);
std::vector<std::span<T>> vec;
while (span.size() >= unit) {
vec.push_back(span.subspan(0, unit));
span = span.subspan(unit);
}
if (!span.empty())
vec.push_back(span);
return vec;
}
static void apply_exclude_libs() {
Timer t("apply_exclude_libs");
if (config.exclude_libs.empty())
return;
std::unordered_set<std::string_view> set(config.exclude_libs.begin(),
config.exclude_libs.end());
for (ObjectFile *file : out::objs)
if (!file->archive_name.empty())
if (set.contains("ALL") || set.contains(file->archive_name))
file->exclude_libs = true;
}
static void create_synthetic_sections() {
auto add = [](OutputChunk *chunk) {
out::chunks.push_back(chunk);
};
add(out::ehdr = new OutputEhdr);
add(out::phdr = new OutputPhdr);
add(out::shdr = new OutputShdr);
add(out::got = new GotSection);
add(out::gotplt = new GotPltSection);
add(out::relplt = new RelPltSection);
if (!config.strip_all)
add(out::strtab = new StrtabSection);
add(out::shstrtab = new ShstrtabSection);
add(out::plt = new PltSection);
add(out::pltgot = new PltGotSection);
if (!config.strip_all)
add(out::symtab = new SymtabSection);
add(out::dynsym = new DynsymSection);
add(out::dynstr = new DynstrSection);
add(out::eh_frame = new EhFrameSection);
add(out::copyrel = new CopyrelSection(".dynbss"));
add(out::copyrel_relro = new CopyrelSection(".dynbss.rel.ro"));
if (!config.dynamic_linker.empty())
add(out::interp = new InterpSection);
if (config.build_id.kind != BuildId::NONE)
add(out::buildid = new BuildIdSection);
if (config.eh_frame_hdr)
add(out::eh_frame_hdr = new EhFrameHdrSection);
if (config.hash_style_sysv)
add(out::hash = new HashSection);
if (config.hash_style_gnu)
add(out::gnu_hash = new GnuHashSection);
if (!config.version_definitions.empty())
add(out::verdef = new VerdefSection);
if (!config.is_static) {
add(out::dynamic = new DynamicSection);
add(out::reldyn = new RelDynSection);
add(out::versym = new VersymSection);
add(out::verneed = new VerneedSection);
}
}
static void set_file_priority() {
// File priority 1 is reserved for the internal file.
i64 priority = 2;
for (ObjectFile *file : out::objs)
if (!file->is_in_lib)
file->priority = priority++;
for (ObjectFile *file : out::objs)
if (file->is_in_lib)
file->priority = priority++;
for (SharedFile *file : out::dsos)
file->priority = priority++;
}
static void resolve_obj_symbols() {
Timer t("resolve_obj_symbols");
// Register archive symbols
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
if (file->is_in_lib)
file->resolve_lazy_symbols();
});
// Register defined symbols
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
if (!file->is_in_lib)
file->resolve_regular_symbols();
});
// Mark reachable objects to decide which files to include
// into an output.
std::vector<ObjectFile *> roots;
for (ObjectFile *file : out::objs)
if (file->is_alive)
roots.push_back(file);
for (std::string_view name : config.undefined)
if (InputFile *file = Symbol::intern(name)->file)
if (!file->is_alive.exchange(true) && !file->is_dso)
roots.push_back((ObjectFile *)file);
tbb::parallel_do(roots,
[&](ObjectFile *file,
tbb::parallel_do_feeder<ObjectFile *> &feeder) {
file->mark_live_objects(
[&](ObjectFile *obj) { feeder.add(obj); });
});
// Remove symbols of eliminated objects.
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
Symbol null_sym;
if (!file->is_alive)
for (Symbol *sym : file->get_global_syms())
if (sym->file == file)
sym->clear();
});
// Eliminate unused archive members.
erase(out::objs, [](InputFile *file) { return !file->is_alive; });
}
static void resolve_dso_symbols() {
Timer t("resolve_dso_symbols");
// Register DSO symbols
tbb::parallel_for_each(out::dsos, [](SharedFile *file) {
file->resolve_symbols();
});
// Mark live DSOs
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
for (i64 i = file->first_global; i < file->elf_syms.size(); i++) {
const ElfSym &esym = file->elf_syms[i];
if (esym.is_defined())
continue;
Symbol &sym = *file->symbols[i];
if (!sym.file || !sym.file->is_dso)
continue;
sym.file->is_alive = true;
if (esym.st_bind != STB_WEAK) {
std::lock_guard lock(sym.mu);
sym.is_weak = false;
}
}
});
// Remove symbols of unreferenced DSOs.
tbb::parallel_for_each(out::dsos, [](SharedFile *file) {
Symbol null_sym;
if (!file->is_alive)
for (Symbol *sym : file->symbols)
if (sym->file == file)
sym->clear();
});
// Remove unreferenced DSOs
erase(out::dsos, [](InputFile *file) { return !file->is_alive; });
}
static void eliminate_comdats() {
Timer t("eliminate_comdats");
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
file->resolve_comdat_groups();
});
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
file->eliminate_duplicate_comdat_groups();
});
}
static void convert_common_symbols() {
Timer t("convert_common_symbols");
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
file->convert_common_symbols();
});
}
static void compute_merged_section_sizes() {
Timer t("compute_merged_section_sizes");
// Mark section fragments referenced by live objects.
if (!config.gc_sections) {
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
for (SectionFragment *frag : file->fragments)
frag->is_alive = true;
});
}
// Add an identification string to .comment.
MergedSection *sec =
MergedSection::get_instance(".comment", SHT_PROGBITS, 0);
std::string_view verstr("mold linker", 12);
SectionFragment *frag = sec->insert(verstr, 1);
frag->is_alive = true;
tbb::parallel_for_each(MergedSection::instances, [](MergedSection *sec) {
sec->assign_offsets();
});
}
// So far, each input section has a pointer to its corresponding
// output section, but there's no reverse edge to get a list of
// input sections from an output section. This function creates it.
//
// An output section may contain millions of input sections.
// So, we append input sections to output sections in parallel.
static void bin_sections() {
Timer t("bin_sections");
i64 unit = (out::objs.size() + 127) / 128;
std::vector<std::span<ObjectFile *>> slices = split(out::objs, unit);
i64 num_osec = OutputSection::instances.size();
std::vector<std::vector<std::vector<InputSection *>>> groups(slices.size());
for (i64 i = 0; i < groups.size(); i++)
groups[i].resize(num_osec);
tbb::parallel_for((i64)0, (i64)slices.size(), [&](i64 i) {
for (ObjectFile *file : slices[i])
for (InputSection *isec : file->sections)
if (isec)
groups[i][isec->output_section->idx].push_back(isec);
});
std::vector<i64> sizes(num_osec);
for (std::span<std::vector<InputSection *>> group : groups)
for (i64 i = 0; i < group.size(); i++)
sizes[i] += group[i].size();
tbb::parallel_for((i64)0, num_osec, [&](i64 j) {
OutputSection::instances[j]->members.reserve(sizes[j]);
for (i64 i = 0; i < groups.size(); i++)
append(OutputSection::instances[j]->members, groups[i][j]);
});
}
static void check_duplicate_symbols() {
Timer t("check_dup_syms");
tbb::parallel_for_each(out::objs, [&](ObjectFile *file) {
for (i64 i = file->first_global; i < file->elf_syms.size(); i++) {
const ElfSym &esym = file->elf_syms[i];
Symbol &sym = *file->symbols[i];
bool is_weak = (esym.st_bind == STB_WEAK);
bool is_eliminated =
!esym.is_abs() && !esym.is_common() && !file->get_section(esym);
if (esym.is_defined() && !is_weak && !is_eliminated && sym.file != file)
Error() << "duplicate symbol: " << *file << ": " << *sym.file
<< ": " << sym;
}
});
Error::checkpoint();
}
std::vector<OutputChunk *> collect_output_sections() {
std::vector<OutputChunk *> vec;
for (OutputSection *osec : OutputSection::instances)
if (!osec->members.empty())
vec.push_back(osec);
for (MergedSection *osec : MergedSection::instances)
if (osec->shdr.sh_size)
vec.push_back(osec);
// Sections are added to the section lists in an arbitrary order because
// they are created in parallel.
// Sort them to to make the output deterministic.
sort(vec, [](OutputChunk *x, OutputChunk *y) {
return std::tuple(x->name, x->shdr.sh_type, x->shdr.sh_flags) <
std::tuple(y->name, y->shdr.sh_type, y->shdr.sh_flags);
});
return vec;
}
static void compute_section_sizes() {
Timer t("compute_section_sizes");
tbb::parallel_for_each(OutputSection::instances, [&](OutputSection *osec) {
if (osec->members.empty())
return;
std::vector<std::span<InputSection *>> slices =
split(osec->members, 10000);
std::vector<i64> size(slices.size());
std::vector<i64> alignments(slices.size());
tbb::parallel_for((i64)0, (i64)slices.size(), [&](i64 i) {
i64 off = 0;
i64 align = 1;
for (InputSection *isec : slices[i]) {
off = align_to(off, isec->shdr.sh_addralign);
isec->offset = off;
off += isec->shdr.sh_size;
align = std::max<i64>(align, isec->shdr.sh_addralign);
}
size[i] = off;
alignments[i] = align;
});
i64 align = *std::max_element(alignments.begin(), alignments.end());
std::vector<i64> start(slices.size());
for (i64 i = 1; i < slices.size(); i++)
start[i] = align_to(start[i - 1] + size[i - 1], align);
tbb::parallel_for((i64)1, (i64)slices.size(), [&](i64 i) {
for (InputSection *isec : slices[i])
isec->offset += start[i];
});
osec->shdr.sh_size = start.back() + size.back();
osec->shdr.sh_addralign = align;
});
}
static void convert_undefined_weak_symbols() {
Timer t("undef_weak");
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
file->convert_undefined_weak_symbols();
});
}
static void scan_rels() {
Timer t("scan_rels");
// Scan relocations to find dynamic symbols.
tbb::parallel_for_each(out::objs, [&](ObjectFile *file) {
file->scan_relocations();
});
// Exit if there was a relocation that refers an undefined symbol.
Error::checkpoint();
// Add imported or exported symbols to .dynsym.
tbb::parallel_for_each(out::objs, [&](ObjectFile *file) {
for (Symbol *sym : file->get_global_syms())
if (sym->file == file)
if (sym->is_imported || sym->is_exported)
sym->flags |= NEEDS_DYNSYM;
});
// Aggregate dynamic symbols to a single vector.
std::vector<InputFile *> files;
append(files, out::objs);
append(files, out::dsos);
std::vector<std::vector<Symbol *>> vec(files.size());
tbb::parallel_for((i64)0, (i64)files.size(), [&](i64 i) {
for (Symbol *sym : files[i]->symbols)
if (sym->flags && sym->file == files[i])
vec[i].push_back(sym);
});
// Assign offsets in additional tables for each dynamic symbol.
for (Symbol *sym : flatten(vec)) {
if (sym->flags & NEEDS_DYNSYM)
out::dynsym->add_symbol(sym);
if (sym->flags & NEEDS_GOT)
out::got->add_got_symbol(sym);
if (sym->flags & NEEDS_PLT) {
if (sym->flags & NEEDS_GOT)
out::pltgot->add_symbol(sym);
else
out::plt->add_symbol(sym);
}
if (sym->flags & NEEDS_GOTTPOFF)
out::got->add_gottpoff_symbol(sym);
if (sym->flags & NEEDS_TLSGD)
out::got->add_tlsgd_symbol(sym);
if (sym->flags & NEEDS_TLSDESC)
out::got->add_tlsdesc_symbol(sym);
if (sym->flags & NEEDS_TLSLD)
out::got->add_tlsld();
if (sym->flags & NEEDS_COPYREL) {
assert(sym->file->is_dso);
SharedFile *file = (SharedFile *)sym->file;
sym->copyrel_readonly = file->is_readonly(sym);
if (sym->copyrel_readonly)
out::copyrel_relro->add_symbol(sym);
else
out::copyrel->add_symbol(sym);
for (Symbol *alias : file->find_aliases(sym)) {
alias->has_copyrel = true;
alias->value = sym->value;
alias->copyrel_readonly = sym->copyrel_readonly;
out::dynsym->add_symbol(alias);
}
}
}
}
static void apply_version_script() {
Timer t("apply_version_script");
for (std::pair<std::string_view, i16> pair : config.version_patterns) {
std::string_view pattern = pair.first;
i16 veridx = pair.second;
assert(pattern != "*");
if (pattern.find('*') == pattern.npos) {
Symbol::intern(pattern)->ver_idx = veridx;
continue;
}
GlobPattern glob(pattern);
tbb::parallel_for_each(out::objs, [&](ObjectFile *file) {
for (Symbol *sym : file->get_global_syms())
if (sym->file == file && glob.match(sym->name))
sym->ver_idx = veridx;
});
}
}
static void parse_symbol_version() {
Timer t("parse_symbol_version");
std::unordered_map<std::string_view, u16> verdefs;
for (i64 i = 0; i < config.version_definitions.size(); i++)
verdefs[config.version_definitions[i]] = i + VER_NDX_LAST_RESERVED + 1;
tbb::parallel_for_each(out::objs, [&](ObjectFile *file) {
for (i64 i = 0; i < file->symbols.size() - file->first_global; i++) {
if (!file->symvers[i])
continue;
Symbol *sym = file->symbols[i + file->first_global];
if (sym->file != file)
continue;
std::string_view ver = file->symvers[i];
bool is_default = false;
if (ver.starts_with('@')) {
is_default = true;
ver = ver.substr(1);
}
auto it = verdefs.find(ver);
if (it == verdefs.end()) {
Error() << *file << ": symbol " << *sym << " has undefined version "
<< ver;
continue;
}
sym->ver_idx = it->second;
if (!is_default)
sym->ver_idx |= VERSYM_HIDDEN;
}
});
}
static void compute_import_export() {
Timer t("compute_import_export");
// Export symbols referenced by DSOs.
if (!config.shared) {
tbb::parallel_for_each(out::dsos, [&](SharedFile *file) {
for (Symbol *sym : file->undefs)
if (sym->file && !sym->file->is_dso && sym->visibility != STV_HIDDEN)
sym->is_exported = true;
});
}
// Global symbols are exported from DSO by default.
if (config.shared || config.export_dynamic) {
tbb::parallel_for_each(out::objs, [](ObjectFile *file) {
for (Symbol *sym : file->get_global_syms()) {
if (sym->file != file)
continue;
if (sym->visibility == STV_HIDDEN || sym->ver_idx == VER_NDX_LOCAL)
continue;
sym->is_exported = true;
if (config.shared && sym->visibility != STV_PROTECTED &&
!config.Bsymbolic &&
!(config.Bsymbolic_functions && sym->get_type() == STT_FUNC))
sym->is_imported = true;
}
});
}
}
static void fill_verdef() {
Timer t("fill_verdef");
if (config.version_definitions.empty())
return;
// Resize .gnu.version
out::versym->contents.resize(out::dynsym->symbols.size(), 1);
out::versym->contents[0] = 0;
// Allocate a buffer for .gnu.version_d.
out::verdef->contents.resize((sizeof(ElfVerdef) + sizeof(ElfVerdaux)) *
(config.version_definitions.size() + 1));
u8 *buf = (u8 *)&out::verdef->contents[0];
u8 *ptr = buf;
ElfVerdef *verdef = nullptr;
auto write = [&](std::string_view verstr, i64 idx, i64 flags) {
out::verdef->shdr.sh_info++;
if (verdef)
verdef->vd_next = ptr - (u8 *)verdef;
verdef = (ElfVerdef *)ptr;
ptr += sizeof(ElfVerdef);
verdef->vd_version = 1;
verdef->vd_flags = flags;
verdef->vd_ndx = idx;
verdef->vd_cnt = 1;
verdef->vd_hash = elf_hash(verstr);
verdef->vd_aux = sizeof(ElfVerdef);
ElfVerdaux *aux = (ElfVerdaux *)ptr;
ptr += sizeof(ElfVerdaux);
aux->vda_name = out::dynstr->add_string(verstr);
};
std::string_view basename = config.soname.empty() ?
config.output : config.soname;
write(basename, 1, VER_FLG_BASE);
i64 idx = 2;
for (std::string_view verstr : config.version_definitions)
write(verstr, idx++, 0);
for (Symbol *sym : std::span(out::dynsym->symbols).subspan(1))
out::versym->contents[sym->dynsym_idx] = sym->ver_idx;
}
static void fill_verneed() {
Timer t("fill_verneed");
// Create a list of versioned symbols and sort by file and version.
std::vector<Symbol *> syms(out::dynsym->symbols.begin() + 1,
out::dynsym->symbols.end());
erase(syms, [](Symbol *sym) {
return !sym->file->is_dso || sym->ver_idx <= VER_NDX_LAST_RESERVED;
});
if (syms.empty())
return;
sort(syms, [](Symbol *a, Symbol *b) {
return std::tuple(((SharedFile *)a->file)->soname, a->ver_idx) <
std::tuple(((SharedFile *)b->file)->soname, b->ver_idx);
});
// Resize of .gnu.version
out::versym->contents.resize(out::dynsym->symbols.size(), 1);
out::versym->contents[0] = 0;
// Allocate a large enough buffer for .gnu.version_r.
out::verneed->contents.resize((sizeof(ElfVerneed) + sizeof(ElfVernaux)) *
syms.size());
// Fill .gnu.version_r.
u8 *buf = (u8 *)&out::verneed->contents[0];
u8 *ptr = buf;
ElfVerneed *verneed = nullptr;
ElfVernaux *aux = nullptr;
u16 veridx = VER_NDX_LAST_RESERVED + config.version_definitions.size();
auto start_group = [&](InputFile *file) {
out::verneed->shdr.sh_info++;
if (verneed)
verneed->vn_next = ptr - (u8 *)verneed;
verneed = (ElfVerneed *)ptr;
ptr += sizeof(*verneed);
verneed->vn_version = 1;
verneed->vn_file = out::dynstr->find_string(((SharedFile *)file)->soname);
verneed->vn_aux = sizeof(ElfVerneed);
aux = nullptr;
};
auto add_entry = [&](Symbol *sym) {
verneed->vn_cnt++;
if (aux)
aux->vna_next = sizeof(ElfVernaux);
aux = (ElfVernaux *)ptr;
ptr += sizeof(*aux);
std::string_view verstr = sym->get_version();
aux->vna_hash = elf_hash(verstr);
aux->vna_other = ++veridx;
aux->vna_name = out::dynstr->add_string(verstr);
};
for (i64 i = 0; i < syms.size(); i++) {
if (i == 0 || syms[i - 1]->file != syms[i]->file) {
start_group(syms[i]->file);
add_entry(syms[i]);
} else if (syms[i - 1]->ver_idx != syms[i]->ver_idx) {
add_entry(syms[i]);
}
out::versym->contents[syms[i]->dynsym_idx] = veridx;
}
// Resize .gnu.version_r to fit to its contents.
out::verneed->contents.resize(ptr - buf);
}
static void clear_padding(i64 filesize) {
Timer t("clear_padding");
auto zero = [](OutputChunk *chunk, i64 next_start) {
i64 pos = chunk->shdr.sh_offset;
if (chunk->shdr.sh_type != SHT_NOBITS)
pos += chunk->shdr.sh_size;
memset(out::buf + pos, 0, next_start - pos);
};
for (i64 i = 1; i < out::chunks.size(); i++)
zero(out::chunks[i - 1], out::chunks[i]->shdr.sh_offset);
zero(out::chunks.back(), filesize);
}
// We want to sort output chunks in the following order.
//
// ELF header
// program header
// .interp
// note
// alloc readonly data
// alloc readonly code
// alloc writable tdata
// alloc writable tbss
// alloc writable RELRO data
// alloc writable RELRO bss
// alloc writable non-RELRO data
// alloc writable non-RELRO bss
// nonalloc
// section header
static i64 get_section_rank(OutputChunk *chunk) {
if (chunk == out::ehdr)
return 0;
if (chunk == out::phdr)
return 1;
if (chunk == out::interp)
return 2;
if (chunk == out::shdr)
return 1 << 20;
u64 type = chunk->shdr.sh_type;
u64 flags = chunk->shdr.sh_flags;
if (type == SHT_NOTE)
return 3;
if (!(flags & SHF_ALLOC))
return (1 << 20) - 1;
bool reaodnly = !(flags & SHF_WRITE);
bool exec = (flags & SHF_EXECINSTR);
bool tls = (flags & SHF_TLS);
bool relro = is_relro(chunk);
bool hasbits = !(type == SHT_NOBITS);
return ((!reaodnly << 9) | (exec << 8) | (!tls << 7) |
(!relro << 6) | (!hasbits << 5)) + 4;
}
// Returns the smallest number n such that
// n >= val and n % align == skew.
inline u64 align_with_skew(u64 val, u64 align, u64 skew) {
return align_to(val + align - skew, align) - align + skew;
}
static i64 set_osec_offsets(std::span<OutputChunk *> chunks) {
Timer t("osec_offset");
i64 fileoff = 0;
i64 vaddr = config.image_base;
for (OutputChunk *chunk : chunks) {
if (chunk->new_page)
vaddr = align_to(vaddr, PAGE_SIZE);
vaddr = align_to(vaddr, chunk->shdr.sh_addralign);
fileoff = align_with_skew(fileoff, PAGE_SIZE, vaddr % PAGE_SIZE);
chunk->shdr.sh_offset = fileoff;
if (chunk->shdr.sh_flags & SHF_ALLOC)
chunk->shdr.sh_addr = vaddr;
bool is_bss = (chunk->shdr.sh_type == SHT_NOBITS);
if (!is_bss)
fileoff += chunk->shdr.sh_size;
bool is_tbss = is_bss && (chunk->shdr.sh_flags & SHF_TLS);
if (!is_tbss)
vaddr += chunk->shdr.sh_size;
if (chunk->new_page_end)
vaddr = align_to(vaddr, PAGE_SIZE);
}
return fileoff;
}
static void fix_synthetic_symbols(std::span<OutputChunk *> chunks) {
auto start = [](Symbol *sym, OutputChunk *chunk) {
if (sym && chunk) {
sym->shndx = chunk->shndx;
sym->value = chunk->shdr.sh_addr;
}
};
auto stop = [](Symbol *sym, OutputChunk *chunk) {
if (sym && chunk) {
sym->shndx = chunk->shndx;
sym->value = chunk->shdr.sh_addr + chunk->shdr.sh_size;
}
};
// __bss_start
for (OutputChunk *chunk : chunks) {
if (chunk->kind == OutputChunk::REGULAR && chunk->name == ".bss") {
start(out::__bss_start, chunk);
break;
}
}
// __ehdr_start and __executable_start
for (OutputChunk *chunk : chunks) {
if (chunk->shndx == 1) {
out::__ehdr_start->shndx = 1;
out::__ehdr_start->value = out::ehdr->shdr.sh_addr;
out::__executable_start->shndx = 1;
out::__executable_start->value = out::ehdr->shdr.sh_addr;
break;
}
}
// __rela_iplt_start and __rela_iplt_end
start(out::__rela_iplt_start, out::relplt);
stop(out::__rela_iplt_end, out::relplt);
// __{init,fini}_array_{start,end}
for (OutputChunk *chunk : chunks) {
switch (chunk->shdr.sh_type) {
case SHT_INIT_ARRAY:
start(out::__init_array_start, chunk);
stop(out::__init_array_end, chunk);
break;
case SHT_FINI_ARRAY:
start(out::__fini_array_start, chunk);
stop(out::__fini_array_end, chunk);
break;
}
}
// _end, _etext, _edata and the like
for (OutputChunk *chunk : chunks) {
if (chunk->kind == OutputChunk::HEADER)
continue;
if (chunk->shdr.sh_flags & SHF_ALLOC)
stop(out::_end, chunk);
if (chunk->shdr.sh_flags & SHF_EXECINSTR)
stop(out::_etext, chunk);
if (chunk->shdr.sh_type != SHT_NOBITS && chunk->shdr.sh_flags & SHF_ALLOC)
stop(out::_edata, chunk);
}
// _DYNAMIC
start(out::_DYNAMIC, out::dynamic);
// _GLOBAL_OFFSET_TABLE_
start(out::_GLOBAL_OFFSET_TABLE_, out::gotplt);
// __GNU_EH_FRAME_HDR
start(out::__GNU_EH_FRAME_HDR, out::eh_frame_hdr);
// __start_ and __stop_ symbols
for (OutputChunk *chunk : chunks) {
if (is_c_identifier(chunk->name)) {
start(Symbol::intern_alloc("__start_" + std::string(chunk->name)), chunk);
stop(Symbol::intern_alloc("__stop_" + std::string(chunk->name)), chunk);
}
}
}
void cleanup() {