tiny.tldr.formats.elf.image.writer

1pub const writer = @import("writer.zig");

1const std = @import("std");2const root = @import("../../../root.zig");3const elf = @import("../root.zig");4const symbols = @import("symbols.zig");5const zero = @import("zero.zig");67const Allocator = std.mem.Allocator;8const model = root.model;9const trace = root.trace;10const StringTable = elf.string.Table;11const ObjectFile = elf.parser.ObjectFile;12const ObjectLayout = elf.layout.ObjectLayout;13const OutputSection = elf.layout.OutputSection;14const GlobalSymbol = elf.layout.GlobalSymbol;15const SymbolRef = elf.layout.SymbolRef;16const GotLayout = elf.layout.GotLayout;17const SymbolAddressCache = elf.addressing.Cache;18const OutputSectionKind = elf.output_section.OutputSectionKind;19const output_section_count = elf.output_section.output_section_count;20const SectionHeader = elf.format.SectionHeader;21const SymbolRecord = elf.format.SymbolRecord;22const ehdr_size = elf.format.ehdr_size;23const phdr_size = elf.format.phdr_size;24const shdr_size = elf.format.shdr_size;25const sym_size = elf.format.sym_size;26const alignForwardU64 = elf.format.alignForwardU64;27const copyInto = elf.format.copyInto;28const elfSymbolInfo = elf.format.elfSymbolInfo;2930pub fn write(31    scratch: Allocator,32    image_allocator: Allocator,33    objects: []const ObjectFile,34    layouts: []const ObjectLayout,35    output_sections: *[output_section_count]OutputSection,36    globals: *const std.StringHashMapUnmanaged(GlobalSymbol),37    global_symbol_refs: []const SymbolRef,38    symbol_addresses: *SymbolAddressCache,39    got_layout: GotLayout,40    options: model.LinkOptions,41    entry_address: u64,42    live_output_count: usize,43    program_header_count: usize,44) model.Error!root.LinkedImage.Storage.Allocation {45    var shstrtab = try StringTable.init(scratch);46    defer shstrtab.deinit(scratch);47    var strtab = try StringTable.init(scratch);48    defer strtab.deinit(scratch);4950    var sh_names: [output_section_count]u32 = @splat(0);51    for (output_sections, 0..) |section, index| {52        if (section.logicalSize() != 0) sh_names[index] = try shstrtab.add(scratch, section.kind.name());53    }54    const sh_name_symtab = try shstrtab.add(scratch, ".symtab");55    const sh_name_strtab = try shstrtab.add(scratch, ".strtab");56    const sh_name_shstrtab = try shstrtab.add(scratch, ".shstrtab");5758    var executable_symbols = std.ArrayListUnmanaged(SymbolRecord).empty;59    defer executable_symbols.deinit(scratch);60    const local_symbol_capacity = std.math.add(usize, 1, live_output_count) catch return error.InvalidObject;61    const executable_symbol_capacity = std.math.add(usize, local_symbol_capacity, global_symbol_refs.len) catch return error.InvalidObject;62    try executable_symbols.ensureTotalCapacity(scratch, executable_symbol_capacity);63    try executable_symbols.append(scratch, .{});64    for (output_sections) |section| {65        if (section.logicalSize() == 0) continue;66        try executable_symbols.append(scratch, .{67            .info = elfSymbolInfo(std.elf.STB_LOCAL, std.elf.STT_SECTION),68            .section_index = section.section_index,69        });70    }71    const first_global_symbol: u32 = @intCast(executable_symbols.items.len);72    {73        const symbol_phase = trace.product(.write_symbol_table);74        defer symbol_phase.end();75        try symbols.appendExecutable(scratch, &executable_symbols, &strtab, objects, layouts, output_sections, globals, global_symbol_refs, symbol_addresses, options.max_link_jobs);76    }7778    const symtab_size = executable_symbols.items.len * sym_size;7980    var last_load_end: u64 = 0;81    for (output_sections) |section| {82        if (section.logicalSize() == 0) continue;83        const file_end = if (section.kind.isNoBits())84            section.file_offset85        else86            section.file_offset + section.fileLoadSize();87        last_load_end = @max(last_load_end, file_end);88    }8990    var metadata_offset = alignForwardU64(last_load_end, 8);91    const symtab_offset = metadata_offset;92    metadata_offset += symtab_size;93    const strtab_offset = metadata_offset;94    metadata_offset += strtab.bytes().len;95    const shstrtab_offset = metadata_offset;96    metadata_offset += shstrtab.bytes().len;97    const shoff = alignForwardU64(metadata_offset, 8);9899    const shnum = 1 + live_output_count + 3;100    if (shnum > std.math.maxInt(u16)) return error.TooManySections;101    const symtab_section_index: u16 = @intCast(1 + live_output_count);102    const strtab_section_index: u16 = symtab_section_index + 1;103    const shstrtab_section_index: u16 = strtab_section_index + 1;104    const total_size = shoff + shnum * shdr_size;105106    var allocation = try root.LinkedImage.Storage.allocate(image_allocator, @intCast(total_size), options);107    errdefer allocation.deinit(image_allocator);108    const image = allocation.bytes;109    if (allocation.needsZeroFill()) {110        const zero_phase = trace.product(.write_zero_fill);111        defer zero_phase.end();112        try zero.unwrittenFileRanges(image, objects, layouts, output_sections, symtab_offset, metadata_offset, shoff);113    }114    try writeGeneratedPayloads(scratch, image, objects, layouts, output_sections, globals, symbol_addresses, options);115    try elf.got_table.writePayload(image, objects, layouts, output_sections, globals, symbol_addresses, got_layout);116117    elf.program.writeElfHeader(image, .{118        .entry_address = entry_address,119        .program_header_count = @intCast(program_header_count),120        .section_header_offset = shoff,121        .section_count = @intCast(shnum),122        .section_string_table_index = shstrtab_section_index,123    });124    elf.program.writeProgramHeaders(image, output_sections, options, program_header_count);125    const metadata_phase = trace.product(.write_metadata);126    const symbol_table = image[@as(usize, @intCast(symtab_offset))..];127    for (executable_symbols.items, 0..) |entry, index| {128        entry.write(symbol_table, index * sym_size);129    }130    copyInto(image, @intCast(strtab_offset), strtab.bytes());131    copyInto(image, @intCast(shstrtab_offset), shstrtab.bytes());132    metadata_phase.end();133134    const section_table = image[@as(usize, @intCast(shoff))..];135    var next_section_index: u16 = 1;136    (SectionHeader{}).write(section_table, 0);137    for (output_sections, 0..) |section, output_index| {138        if (section.logicalSize() == 0) continue;139        (SectionHeader{140            .name_offset = sh_names[output_index],141            .section_type = section.kind.sectionType(),142            .flags = section.kind.flags(),143            .address = section.address,144            .offset = section.file_offset,145            .size = section.logicalSize(),146            .alignment = section.alignment,147            .entry_size = section.kind.entrySize(),148        }).write(section_table, @as(usize, next_section_index) * shdr_size);149        next_section_index += 1;150    }151    (SectionHeader{152        .name_offset = sh_name_symtab,153        .section_type = std.elf.SHT_SYMTAB,154        .offset = symtab_offset,155        .size = symtab_size,156        .link = strtab_section_index,157        .info = first_global_symbol,158        .alignment = 8,159        .entry_size = sym_size,160    }).write(section_table, @as(usize, symtab_section_index) * shdr_size);161    (SectionHeader{162        .name_offset = sh_name_strtab,163        .section_type = std.elf.SHT_STRTAB,164        .offset = strtab_offset,165        .size = strtab.bytes().len,166        .alignment = 1,167    }).write(section_table, @as(usize, strtab_section_index) * shdr_size);168    (SectionHeader{169        .name_offset = sh_name_shstrtab,170        .section_type = std.elf.SHT_STRTAB,171        .offset = shstrtab_offset,172        .size = shstrtab.bytes().len,173        .alignment = 1,174    }).write(section_table, @as(usize, shstrtab_section_index) * shdr_size);175176    return allocation;177}178179fn writeGeneratedPayloads(180    scratch: Allocator,181    image: []u8,182    objects: []const ObjectFile,183    layouts: []const ObjectLayout,184    output_sections: []const OutputSection,185    globals: *const std.StringHashMapUnmanaged(GlobalSymbol),186    symbol_addresses: *SymbolAddressCache,187    options: model.LinkOptions,188) model.Error!void {189    if (options.build_id != .none) {190        const section = output_sections[@backingInt(OutputSectionKind.build_id_note)];191        try elf.note.writeBuildIdHeader(image, section.file_offset);192    }193    try elf.ehframe.writeHeader(scratch, image, objects, layouts, output_sections, globals, symbol_addresses, options);194}