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180 lines
4.9 KiB
C++
180 lines
4.9 KiB
C++
// This file contains functions to read an archive file (.a file).
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// An archive file is just a bundle of object files. It's similar to
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// tar or zip, but the contents are not compressed.
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//
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// An archive file is either "regular" or "thin". A regular archive
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// contains object files directly, while a thin archive contains only
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// pathnames. In the latter case, actual file contents have to be read
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// from given pathnames. A regular archive is sometimes called "fat"
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// archive as opposed to "thin".
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//
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// If an archive file is given to the linker, the linker pulls out
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// object files that are needed to resolve undefined symbols. So,
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// bunding object files as an archive and giving that archive to the
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// linker has a different meaning than directly giving the same set of
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// object files to the linker. The former links only needed object
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// files, while the latter links all the given object files.
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//
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// Therefore, if you link libc.a for example, not all the libc
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// functions are linked to your binary. Instead, only object files
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// that provides functions and variables used in your program get
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// linked. To make this efficient, static library functions are
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// usually separated to each object file in an archive file. You can
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// see the contents of libc.a by runnning `ar t
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// /usr/lib/x86_64-linux-gnu/libc.a`.
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#pragma once
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#include "mold.h"
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#include "filetype.h"
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namespace mold {
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struct ArHdr {
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char ar_name[16];
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char ar_date[12];
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char ar_uid[6];
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char ar_gid[6];
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char ar_mode[8];
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char ar_size[10];
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char ar_fmag[2];
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bool starts_with(std::string_view s) const {
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return std::string_view(ar_name, s.size()) == s;
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}
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bool is_strtab() const {
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return starts_with("// ");
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}
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bool is_symtab() const {
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return starts_with("/ ") || starts_with("/SYM64/ ");
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}
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std::string read_name(std::string_view strtab, u8 *&ptr) const {
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// BSD-style long filename
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if (starts_with("#1/")) {
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int namelen = atoi(ar_name + 3);
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std::string name{(char *)ptr, (size_t)namelen};
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ptr += namelen;
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if (size_t pos = name.find('\0'))
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name = name.substr(0, pos);
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return name;
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}
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// SysV-style long filename
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if (starts_with("/")) {
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const char *start = strtab.data() + atoi(ar_name + 1);
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return {start, (const char *)strstr(start, "/\n")};
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}
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// Short fileanme
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if (const char *end = (char *)memchr(ar_name, '/', sizeof(ar_name)))
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return {ar_name, end};
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return {ar_name, sizeof(ar_name)};
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}
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};
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template <typename C>
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std::vector<MappedFile<C> *>
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read_thin_archive_members(C &ctx, MappedFile<C> *mf) {
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u8 *begin = mf->data;
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u8 *data = begin + 8;
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std::vector<MappedFile<C> *> vec;
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std::string_view strtab;
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while (data < begin + mf->size) {
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// Each header is aligned to a 2 byte boundary.
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if ((begin - data) % 2)
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data++;
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ArHdr &hdr = *(ArHdr *)data;
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u8 *body = data + sizeof(hdr);
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u64 size = atol(hdr.ar_size);
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// Read a string table.
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if (hdr.is_strtab()) {
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strtab = {(char *)body, (size_t)size};
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data = body + size;
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continue;
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}
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// Skip a symbol table.
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if (hdr.is_symtab()) {
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data = body + size;
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continue;
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}
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if (!hdr.starts_with("#1/") && !hdr.starts_with("/"))
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Fatal(ctx) << mf->name << ": filename is not stored as a long filename";
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std::string name = hdr.read_name(strtab, body);
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// Skip if symbol table
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if (name == "__.SYMDEF" || name == "__.SYMDEF SORTED")
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continue;
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std::string path = name.starts_with('/') ?
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name : (filepath(mf->name).parent_path() / name).string();
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vec.push_back(MappedFile<C>::must_open(ctx, path));
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vec.back()->thin_parent = mf;
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data = body;
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}
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return vec;
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}
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template <typename C>
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std::vector<MappedFile<C> *>
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read_fat_archive_members(C &ctx, MappedFile<C> *mf) {
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u8 *begin = mf->data;
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u8 *data = begin + 8;
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std::vector<MappedFile<C> *> vec;
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std::string_view strtab;
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while (begin + mf->size - data >= 2) {
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if ((begin - data) % 2)
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data++;
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ArHdr &hdr = *(ArHdr *)data;
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u8 *body = data + sizeof(hdr);
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u64 size = atol(hdr.ar_size);
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data = body + size;
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// Read if string table
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if (hdr.is_strtab()) {
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strtab = {(char *)body, (size_t)size};
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continue;
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}
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// Skip if symbol table
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if (hdr.is_symtab())
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continue;
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// Read the name field
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std::string name = hdr.read_name(strtab, body);
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// Skip if symbol table
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if (name == "__.SYMDEF" || name == "__.SYMDEF SORTED")
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continue;
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vec.push_back(mf->slice(ctx, name, body - begin, data - body));
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}
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return vec;
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}
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template <typename C>
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std::vector<MappedFile<C> *>
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read_archive_members(C &ctx, MappedFile<C> *mf) {
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switch (get_file_type(mf)) {
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case FileType::AR:
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return read_fat_archive_members(ctx, mf);
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case FileType::THIN_AR:
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return read_thin_archive_members(ctx, mf);
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default:
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unreachable();
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}
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}
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} // namespace mold
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