link.zig

const std = @import("std");
const build_options = @import("build_options");
const builtin = @import("builtin");
const assert = std.debug.assert;
const fs = std.fs;
const mem = std.mem;
const log = std.log.scoped(.link);
const trace = @import("tracy.zig").trace;
const wasi_libc = @import("wasi_libc.zig");

const Air = @import("Air.zig");
const Allocator = std.mem.Allocator;
const Cache = @import("Cache.zig");
const Compilation = @import("Compilation.zig");
const LibCInstallation = @import("libc_installation.zig").LibCInstallation;
const Liveness = @import("Liveness.zig");
const Module = @import("Module.zig");
const Package = @import("Package.zig");
const Type = @import("type.zig").Type;
const TypedValue = @import("TypedValue.zig");

/// When adding a new field, remember to update `hashAddSystemLibs`.
pub const SystemLib = struct {
    needed: bool = false,
    weak: bool = false,
};

pub const CacheMode = enum { incremental, whole };

pub fn hashAddSystemLibs(
    hh: *Cache.HashHelper,
    hm: std.StringArrayHashMapUnmanaged(SystemLib),
) void {
    const keys = hm.keys();
    hh.add(keys.len);
    hh.addListOfBytes(keys);
    for (hm.values()) |value| {
        hh.add(value.needed);
        hh.add(value.weak);
    }
}

pub const producer_string = if (builtin.is_test) "zig test" else "zig " ++ build_options.version;

pub const Emit = struct {
    /// Where the output will go.
    directory: Compilation.Directory,
    /// Path to the output file, relative to `directory`.
    sub_path: []const u8,

    /// Returns the full path to `basename` if it were in the same directory as the
    /// `Emit` sub_path.
    pub fn basenamePath(emit: Emit, arena: Allocator, basename: [:0]const u8) ![:0]const u8 {
        const full_path = if (emit.directory.path) |p|
            try fs.path.join(arena, &[_][]const u8{ p, emit.sub_path })
        else
            emit.sub_path;

        if (fs.path.dirname(full_path)) |dirname| {
            return try fs.path.joinZ(arena, &.{ dirname, basename });
        } else {
            return basename;
        }
    }
};

pub const Options = struct {
    /// This is `null` when `-fno-emit-bin` is used.
    emit: ?Emit,
    /// This is `null` not building a Windows DLL, or when `-fno-emit-implib` is used.
    implib_emit: ?Emit,
    target: std.Target,
    output_mode: std.builtin.OutputMode,
    link_mode: std.builtin.LinkMode,
    optimize_mode: std.builtin.Mode,
    machine_code_model: std.builtin.CodeModel,
    root_name: [:0]const u8,
    /// Not every Compilation compiles .zig code! For example you could do `zig build-exe foo.o`.
    module: ?*Module,
    dynamic_linker: ?[]const u8,
    /// The root path for the dynamic linker and system libraries (as well as frameworks on Darwin)
    sysroot: ?[]const u8,
    /// Used for calculating how much space to reserve for symbols in case the binary file
    /// does not already have a symbol table.
    symbol_count_hint: u64 = 32,
    /// Used for calculating how much space to reserve for executable program code in case
    /// the binary file does not already have such a section.
    program_code_size_hint: u64 = 256 * 1024,
    entry_addr: ?u64 = null,
    entry: ?[]const u8,
    stack_size_override: ?u64,
    image_base_override: ?u64,
    /// 0 means no stack protector
    /// other value means stack protector with that buffer size.
    stack_protector: u32,
    cache_mode: CacheMode,
    include_compiler_rt: bool,
    /// Set to `true` to omit debug info.
    strip: bool,
    /// If this is true then this link code is responsible for outputting an object
    /// file and then using LLD to link it together with the link options and other objects.
    /// Otherwise (depending on `use_llvm`) this link code directly outputs and updates the final binary.
    use_lld: bool,
    /// If this is true then this link code is responsible for making an LLVM IR Module,
    /// outputting it to an object file, and then linking that together with link options and
    /// other objects.
    /// Otherwise (depending on `use_lld`) this link code directly outputs and updates the final binary.
    use_llvm: bool,
    link_libc: bool,
    link_libcpp: bool,
    link_libunwind: bool,
    function_sections: bool,
    no_builtin: bool,
    eh_frame_hdr: bool,
    emit_relocs: bool,
    rdynamic: bool,
    z_nodelete: bool,
    z_notext: bool,
    z_defs: bool,
    z_origin: bool,
    z_nocopyreloc: bool,
    z_now: bool,
    z_relro: bool,
    tsaware: bool,
    nxcompat: bool,
    dynamicbase: bool,
    linker_optimization: u8,
    compress_debug_sections: CompressDebugSections,
    bind_global_refs_locally: bool,
    import_memory: bool,
    import_table: bool,
    export_table: bool,
    initial_memory: ?u64,
    max_memory: ?u64,
    shared_memory: bool,
    export_symbol_names: []const []const u8,
    global_base: ?u64,
    is_native_os: bool,
    is_native_abi: bool,
    pic: bool,
    pie: bool,
    lto: bool,
    valgrind: bool,
    tsan: bool,
    stack_check: bool,
    red_zone: bool,
    omit_frame_pointer: bool,
    single_threaded: bool,
    verbose_link: bool,
    dll_export_fns: bool,
    error_return_tracing: bool,
    skip_linker_dependencies: bool,
    parent_compilation_link_libc: bool,
    each_lib_rpath: bool,
    build_id: bool,
    disable_lld_caching: bool,
    is_test: bool,
    hash_style: HashStyle,
    major_subsystem_version: ?u32,
    minor_subsystem_version: ?u32,
    gc_sections: ?bool = null,
    allow_shlib_undefined: ?bool,
    subsystem: ?std.Target.SubSystem,
    linker_script: ?[]const u8,
    version_script: ?[]const u8,
    soname: ?[]const u8,
    llvm_cpu_features: ?[*:0]const u8,
    print_gc_sections: bool,
    print_icf_sections: bool,
    print_map: bool,

    objects: []Compilation.LinkObject,
    framework_dirs: []const []const u8,
    frameworks: std.StringArrayHashMapUnmanaged(SystemLib),
    system_libs: std.StringArrayHashMapUnmanaged(SystemLib),
    wasi_emulated_libs: []const wasi_libc.CRTFile,
    lib_dirs: []const []const u8,
    rpath_list: []const []const u8,

    /// List of symbols forced as undefined in the symbol table
    /// thus forcing their resolution by the linker.
    /// Corresponds to `-u <symbol>` for ELF and `/include:<symbol>` for COFF/PE.
    /// TODO add handling for MachO.
    force_undefined_symbols: std.StringArrayHashMapUnmanaged(void),

    version: ?std.builtin.Version,
    compatibility_version: ?std.builtin.Version,
    libc_installation: ?*const LibCInstallation,

    /// WASI-only. Type of WASI execution model ("command" or "reactor").
    wasi_exec_model: std.builtin.WasiExecModel = undefined,

    /// (Zig compiler development) Enable dumping of linker's state as JSON.
    enable_link_snapshots: bool = false,

    /// (Darwin) Path and version of the native SDK if detected.
    native_darwin_sdk: ?std.zig.system.darwin.DarwinSDK = null,

    /// (Darwin) Install name for the dylib
    install_name: ?[]const u8 = null,

    /// (Darwin) Path to entitlements file
    entitlements: ?[]const u8 = null,

    /// (Darwin) size of the __PAGEZERO segment
    pagezero_size: ?u64 = null,

    /// (Darwin) search strategy for system libraries
    search_strategy: ?File.MachO.SearchStrategy = null,

    /// (Darwin) set minimum space for future expansion of the load commands
    headerpad_size: ?u32 = null,

    /// (Darwin) set enough space as if all paths were MATPATHLEN
    headerpad_max_install_names: bool = false,

    /// (Darwin) remove dylibs that are unreachable by the entry point or exported symbols
    dead_strip_dylibs: bool = false,

    pub fn effectiveOutputMode(options: Options) std.builtin.OutputMode {
        return if (options.use_lld) .Obj else options.output_mode;
    }

    pub fn move(self: *Options) Options {
        const copied_state = self.*;
        self.system_libs = .{};
        return copied_state;
    }
};

pub const HashStyle = enum { sysv, gnu, both };

pub const CompressDebugSections = enum { none, zlib };

pub const File = struct {
    tag: Tag,
    options: Options,
    file: ?fs.File,
    allocator: Allocator,
    /// When linking with LLD, this linker code will output an object file only at
    /// this location, and then this path can be placed on the LLD linker line.
    intermediary_basename: ?[]const u8 = null,

    /// Prevents other processes from clobbering files in the output directory
    /// of this linking operation.
    lock: ?Cache.Lock = null,

    pub const LinkBlock = union {
        elf: Elf.TextBlock,
        coff: Coff.Atom,
        macho: MachO.Atom,
        plan9: Plan9.DeclBlock,
        c: void,
        wasm: Wasm.DeclBlock,
        spirv: void,
        nvptx: void,
    };

    pub const LinkFn = union {
        elf: Dwarf.SrcFn,
        coff: Coff.SrcFn,
        macho: Dwarf.SrcFn,
        plan9: void,
        c: void,
        wasm: Wasm.FnData,
        spirv: SpirV.FnData,
        nvptx: void,
    };

    pub const Export = union {
        elf: Elf.Export,
        coff: Coff.Export,
        macho: MachO.Export,
        plan9: Plan9.Export,
        c: void,
        wasm: Wasm.Export,
        spirv: void,
        nvptx: void,
    };

    /// Attempts incremental linking, if the file already exists. If
    /// incremental linking fails, falls back to truncating the file and
    /// rewriting it. A malicious file is detected as incremental link failure
    /// and does not cause Illegal Behavior. This operation is not atomic.
    pub fn openPath(allocator: Allocator, options: Options) !*File {
        const have_macho = !build_options.only_c;
        if (have_macho and options.target.ofmt == .macho) {
            return &(try MachO.openPath(allocator, options)).base;
        }

        if (options.emit == null) {
            return switch (options.target.ofmt) {
                .coff => &(try Coff.createEmpty(allocator, options)).base,
                .elf => &(try Elf.createEmpty(allocator, options)).base,
                .macho => unreachable,
                .wasm => &(try Wasm.createEmpty(allocator, options)).base,
                .plan9 => return &(try Plan9.createEmpty(allocator, options)).base,
                .c => unreachable, // Reported error earlier.
                .spirv => &(try SpirV.createEmpty(allocator, options)).base,
                .nvptx => &(try NvPtx.createEmpty(allocator, options)).base,
                .hex => return error.HexObjectFormatUnimplemented,
                .raw => return error.RawObjectFormatUnimplemented,
                .dxcontainer => return error.DirectXContainerObjectFormatUnimplemented,
            };
        }
        const emit = options.emit.?;
        const use_lld = build_options.have_llvm and options.use_lld; // comptime-known false when !have_llvm
        const sub_path = if (use_lld) blk: {
            if (options.module == null) {
                // No point in opening a file, we would not write anything to it.
                // Initialize with empty.
                return switch (options.target.ofmt) {
                    .coff => &(try Coff.createEmpty(allocator, options)).base,
                    .elf => &(try Elf.createEmpty(allocator, options)).base,
                    .macho => unreachable,
                    .plan9 => &(try Plan9.createEmpty(allocator, options)).base,
                    .wasm => &(try Wasm.createEmpty(allocator, options)).base,
                    .c => unreachable, // Reported error earlier.
                    .spirv => &(try SpirV.createEmpty(allocator, options)).base,
                    .nvptx => &(try NvPtx.createEmpty(allocator, options)).base,
                    .hex => return error.HexObjectFormatUnimplemented,
                    .raw => return error.RawObjectFormatUnimplemented,
                    .dxcontainer => return error.DirectXContainerObjectFormatUnimplemented,
                };
            }
            // Open a temporary object file, not the final output file because we
            // want to link with LLD.
            break :blk try std.fmt.allocPrint(allocator, "{s}{s}", .{
                emit.sub_path, options.target.ofmt.fileExt(options.target.cpu.arch),
            });
        } else emit.sub_path;
        errdefer if (use_lld) allocator.free(sub_path);

        const file: *File = f: {
            switch (options.target.ofmt) {
                .coff => {
                    if (build_options.only_c) unreachable;
                    break :f &(try Coff.openPath(allocator, sub_path, options)).base;
                },
                .elf => {
                    if (build_options.only_c) unreachable;
                    break :f &(try Elf.openPath(allocator, sub_path, options)).base;
                },
                .macho => unreachable,
                .plan9 => {
                    if (build_options.only_c) unreachable;
                    break :f &(try Plan9.openPath(allocator, sub_path, options)).base;
                },
                .wasm => {
                    if (build_options.only_c) unreachable;
                    break :f &(try Wasm.openPath(allocator, sub_path, options)).base;
                },
                .c => {
                    break :f &(try C.openPath(allocator, sub_path, options)).base;
                },
                .spirv => {
                    if (build_options.only_c) unreachable;
                    break :f &(try SpirV.openPath(allocator, sub_path, options)).base;
                },
                .nvptx => {
                    if (build_options.only_c) unreachable;
                    break :f &(try NvPtx.openPath(allocator, sub_path, options)).base;
                },
                .hex => return error.HexObjectFormatUnimplemented,
                .raw => return error.RawObjectFormatUnimplemented,
                .dxcontainer => return error.DirectXContainerObjectFormatUnimplemented,
            }
        };

        if (use_lld) {
            // TODO this intermediary_basename isn't enough; in the case of `zig build-exe`,
            // we also want to put the intermediary object file in the cache while the
            // main emit directory is the cwd.
            file.intermediary_basename = sub_path;
        }

        return file;
    }

    pub fn cast(base: *File, comptime T: type) ?*T {
        if (base.tag != T.base_tag)
            return null;

        return @fieldParentPtr(T, "base", base);
    }

    pub fn makeWritable(base: *File) !void {
        switch (base.tag) {
            .coff, .elf, .macho, .plan9, .wasm => {
                if (build_options.only_c) unreachable;
                if (base.file != null) return;
                const emit = base.options.emit orelse return;
                base.file = try emit.directory.handle.createFile(emit.sub_path, .{
                    .truncate = false,
                    .read = true,
                    .mode = determineMode(base.options),
                });
            },
            .c, .spirv, .nvptx => {},
        }
    }

    pub fn makeExecutable(base: *File) !void {
        switch (base.options.output_mode) {
            .Obj => return,
            .Lib => switch (base.options.link_mode) {
                .Static => return,
                .Dynamic => {},
            },
            .Exe => {},
        }
        switch (base.tag) {
            .macho => if (base.file) |f| {
                if (build_options.only_c) unreachable;
                if (comptime builtin.target.isDarwin() and builtin.target.cpu.arch == .aarch64) {
                    if (base.options.target.cpu.arch == .aarch64) {
                        // XNU starting with Big Sur running on arm64 is caching inodes of running binaries.
                        // Any change to the binary will effectively invalidate the kernel's cache
                        // resulting in a SIGKILL on each subsequent run. Since when doing incremental
                        // linking we're modifying a binary in-place, this will end up with the kernel
                        // killing it on every subsequent run. To circumvent it, we will copy the file
                        // into a new inode, remove the original file, and rename the copy to match
                        // the original file. This is super messy, but there doesn't seem any other
                        // way to please the XNU.
                        const emit = base.options.emit orelse return;
                        try emit.directory.handle.copyFile(emit.sub_path, emit.directory.handle, emit.sub_path, .{});
                    }
                }
                f.close();
                base.file = null;
            },
            .coff, .elf, .plan9, .wasm => if (base.file) |f| {
                if (build_options.only_c) unreachable;
                if (base.intermediary_basename != null) {
                    // The file we have open is not the final file that we want to
                    // make executable, so we don't have to close it.
                    return;
                }
                f.close();
                base.file = null;
            },
            .c, .spirv, .nvptx => {},
        }
    }

    pub const UpdateDeclError = error{
        OutOfMemory,
        Overflow,
        Underflow,
        FileTooBig,
        InputOutput,
        FilesOpenedWithWrongFlags,
        IsDir,
        NoSpaceLeft,
        Unseekable,
        PermissionDenied,
        SwapFile,
        CorruptedData,
        SystemResources,
        OperationAborted,
        BrokenPipe,
        ConnectionResetByPeer,
        ConnectionTimedOut,
        NotOpenForReading,
        WouldBlock,
        AccessDenied,
        Unexpected,
        DiskQuota,
        NotOpenForWriting,
        AnalysisFail,
        CodegenFail,
        EmitFail,
        NameTooLong,
        CurrentWorkingDirectoryUnlinked,
        LockViolation,
    };

    /// Called from within the CodeGen to lower a local variable instantion as an unnamed
    /// constant. Returns the symbol index of the lowered constant in the read-only section
    /// of the final binary.
    pub fn lowerUnnamedConst(base: *File, tv: TypedValue, decl_index: Module.Decl.Index) UpdateDeclError!u32 {
        if (build_options.only_c) @compileError("unreachable");
        const decl = base.options.module.?.declPtr(decl_index);
        log.debug("lowerUnnamedConst {*} ({s})", .{ decl, decl.name });
        switch (base.tag) {
            // zig fmt: off
            .coff  => return @fieldParentPtr(Coff,  "base", base).lowerUnnamedConst(tv, decl_index),
            .elf   => return @fieldParentPtr(Elf,   "base", base).lowerUnnamedConst(tv, decl_index),
            .macho => return @fieldParentPtr(MachO, "base", base).lowerUnnamedConst(tv, decl_index),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).lowerUnnamedConst(tv, decl_index),
            .spirv => unreachable,
            .c     => unreachable,
            .wasm  => return @fieldParentPtr(Wasm,  "base", base).lowerUnnamedConst(tv, decl_index),
            .nvptx => unreachable,
            // zig fmt: on
        }
    }

    /// Called from within CodeGen to retrieve the symbol index of a global symbol.
    /// If no symbol exists yet with this name, a new undefined global symbol will
    /// be created. This symbol may get resolved once all relocatables are (re-)linked.
    pub fn getGlobalSymbol(base: *File, name: []const u8) UpdateDeclError!u32 {
        if (build_options.only_c) @compileError("unreachable");
        log.debug("getGlobalSymbol '{s}'", .{name});
        switch (base.tag) {
            // zig fmt: off
            .coff  => return @fieldParentPtr(Coff, "base", base).getGlobalSymbol(name),
            .elf   => unreachable,
            .macho => return @fieldParentPtr(MachO, "base", base).getGlobalSymbol(name),
            .plan9 => unreachable,
            .spirv => unreachable,
            .c     => unreachable,
            .wasm  => return @fieldParentPtr(Wasm,  "base", base).getGlobalSymbol(name),
            .nvptx => unreachable,
            // zig fmt: on
        }
    }

    /// May be called before or after updateDeclExports but must be called
    /// after allocateDeclIndexes for any given Decl.
    pub fn updateDecl(base: *File, module: *Module, decl_index: Module.Decl.Index) UpdateDeclError!void {
        const decl = module.declPtr(decl_index);
        log.debug("updateDecl {*} ({s}), type={}", .{ decl, decl.name, decl.ty.fmtDebug() });
        assert(decl.has_tv);
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).updateDecl(module, decl_index);
        }
        switch (base.tag) {
            // zig fmt: off
            .coff  => return @fieldParentPtr(Coff,  "base", base).updateDecl(module, decl_index),
            .elf   => return @fieldParentPtr(Elf,   "base", base).updateDecl(module, decl_index),
            .macho => return @fieldParentPtr(MachO, "base", base).updateDecl(module, decl_index),
            .c     => return @fieldParentPtr(C,     "base", base).updateDecl(module, decl_index),
            .wasm  => return @fieldParentPtr(Wasm,  "base", base).updateDecl(module, decl_index),
            .spirv => return @fieldParentPtr(SpirV, "base", base).updateDecl(module, decl_index),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).updateDecl(module, decl_index),
            .nvptx => return @fieldParentPtr(NvPtx, "base", base).updateDecl(module, decl_index),
            // zig fmt: on
        }
    }

    /// May be called before or after updateDeclExports but must be called
    /// after allocateDeclIndexes for any given Decl.
    pub fn updateFunc(base: *File, module: *Module, func: *Module.Fn, air: Air, liveness: Liveness) UpdateDeclError!void {
        const owner_decl = module.declPtr(func.owner_decl);
        log.debug("updateFunc {*} ({s}), type={}", .{
            owner_decl, owner_decl.name, owner_decl.ty.fmtDebug(),
        });
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).updateFunc(module, func, air, liveness);
        }
        switch (base.tag) {
            // zig fmt: off
            .coff  => return @fieldParentPtr(Coff,  "base", base).updateFunc(module, func, air, liveness),
            .elf   => return @fieldParentPtr(Elf,   "base", base).updateFunc(module, func, air, liveness),
            .macho => return @fieldParentPtr(MachO, "base", base).updateFunc(module, func, air, liveness),
            .c     => return @fieldParentPtr(C,     "base", base).updateFunc(module, func, air, liveness),
            .wasm  => return @fieldParentPtr(Wasm,  "base", base).updateFunc(module, func, air, liveness),
            .spirv => return @fieldParentPtr(SpirV, "base", base).updateFunc(module, func, air, liveness),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).updateFunc(module, func, air, liveness),
            .nvptx => return @fieldParentPtr(NvPtx, "base", base).updateFunc(module, func, air, liveness),
            // zig fmt: on
        }
    }

    pub fn updateDeclLineNumber(base: *File, module: *Module, decl: *Module.Decl) UpdateDeclError!void {
        log.debug("updateDeclLineNumber {*} ({s}), line={}", .{
            decl, decl.name, decl.src_line + 1,
        });
        assert(decl.has_tv);
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).updateDeclLineNumber(module, decl);
        }
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).updateDeclLineNumber(module, decl),
            .elf => return @fieldParentPtr(Elf, "base", base).updateDeclLineNumber(module, decl),
            .macho => return @fieldParentPtr(MachO, "base", base).updateDeclLineNumber(module, decl),
            .c => return @fieldParentPtr(C, "base", base).updateDeclLineNumber(module, decl),
            .wasm => return @fieldParentPtr(Wasm, "base", base).updateDeclLineNumber(module, decl),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).updateDeclLineNumber(module, decl),
            .spirv, .nvptx => {},
        }
    }

    /// Must be called before any call to updateDecl or updateDeclExports for
    /// any given Decl.
    /// TODO we're transitioning to deleting this function and instead having
    /// each linker backend notice the first time updateDecl or updateFunc is called, or
    /// a callee referenced from AIR.
    pub fn allocateDeclIndexes(base: *File, decl_index: Module.Decl.Index) error{OutOfMemory}!void {
        const decl = base.options.module.?.declPtr(decl_index);
        log.debug("allocateDeclIndexes {*} ({s})", .{ decl, decl.name });
        if (build_options.only_c) {
            assert(base.tag == .c);
            return;
        }
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).allocateDeclIndexes(decl_index),
            .elf => return @fieldParentPtr(Elf, "base", base).allocateDeclIndexes(decl_index),
            .macho => return @fieldParentPtr(MachO, "base", base).allocateDeclIndexes(decl_index),
            .wasm => return @fieldParentPtr(Wasm, "base", base).allocateDeclIndexes(decl_index),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).allocateDeclIndexes(decl_index),
            .c, .spirv, .nvptx => {},
        }
    }

    pub fn releaseLock(self: *File) void {
        if (self.lock) |*lock| {
            lock.release();
            self.lock = null;
        }
    }

    pub fn toOwnedLock(self: *File) Cache.Lock {
        const lock = self.lock.?;
        self.lock = null;
        return lock;
    }

    pub fn destroy(base: *File) void {
        base.releaseLock();
        if (base.file) |f| f.close();
        if (base.intermediary_basename) |sub_path| base.allocator.free(sub_path);
        base.options.system_libs.deinit(base.allocator);
        switch (base.tag) {
            .coff => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(Coff, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .elf => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(Elf, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .macho => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(MachO, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .c => {
                const parent = @fieldParentPtr(C, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .wasm => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(Wasm, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .spirv => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(SpirV, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .plan9 => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(Plan9, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
            .nvptx => {
                if (build_options.only_c) unreachable;
                const parent = @fieldParentPtr(NvPtx, "base", base);
                parent.deinit();
                base.allocator.destroy(parent);
            },
        }
    }

    /// TODO audit this error set. most of these should be collapsed into one error,
    /// and ErrorFlags should be updated to convey the meaning to the user.
    pub const FlushError = error{
        CacheUnavailable,
        CurrentWorkingDirectoryUnlinked,
        DivisionByZero,
        DllImportLibraryNotFound,
        EmptyStubFile,
        ExpectedFuncType,
        FailedToEmit,
        FailedToResolveRelocationTarget,
        FileSystem,
        FilesOpenedWithWrongFlags,
        FlushFailure,
        FrameworkNotFound,
        FunctionSignatureMismatch,
        GlobalTypeMismatch,
        InvalidCharacter,
        InvalidEntryKind,
        InvalidFeatureSet,
        InvalidFormat,
        InvalidIndex,
        InvalidMagicByte,
        InvalidWasmVersion,
        LLDCrashed,
        LLDReportedFailure,
        LLD_LinkingIsTODO_ForSpirV,
        LibCInstallationMissingCRTDir,
        LibCInstallationNotAvailable,
        LibraryNotFound,
        LinkingWithoutZigSourceUnimplemented,
        MalformedArchive,
        MalformedDwarf,
        MalformedSection,
        MemoryTooBig,
        MemoryTooSmall,
        MismatchedCpuArchitecture,
        MissAlignment,
        MissingEndForBody,
        MissingEndForExpression,
        /// TODO: this should be removed from the error set in favor of using ErrorFlags
        MissingMainEntrypoint,
        MissingSymbol,
        MissingTableSymbols,
        ModuleNameMismatch,
        MultipleSymbolDefinitions,
        NoObjectsToLink,
        NotObject,
        NotObjectFile,
        NotSupported,
        OutOfMemory,
        Overflow,
        PermissionDenied,
        StreamTooLong,
        SwapFile,
        SymbolCollision,
        SymbolMismatchingType,
        TODOImplementPlan9Objs,
        TODOImplementWritingLibFiles,
        TODOImplementWritingStaticLibFiles,
        UnableToSpawnSelf,
        UnableToSpawnWasm,
        UnableToWriteArchive,
        UndefinedLocal,
        /// TODO: merge with UndefinedSymbolReference
        UndefinedSymbol,
        /// TODO: merge with UndefinedSymbol
        UndefinedSymbolReference,
        Underflow,
        UnexpectedRemainder,
        UnexpectedTable,
        UnexpectedValue,
        UnhandledDwFormValue,
        UnhandledSymbolType,
        UnknownFeature,
        Unseekable,
        UnsupportedCpuArchitecture,
        UnsupportedVersion,
    } ||
        fs.File.WriteFileError ||
        fs.File.OpenError ||
        std.ChildProcess.SpawnError ||
        fs.Dir.CopyFileError;

    /// Commit pending changes and write headers. Takes into account final output mode
    /// and `use_lld`, not only `effectiveOutputMode`.
    pub fn flush(base: *File, comp: *Compilation, prog_node: *std.Progress.Node) FlushError!void {
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).flush(comp, prog_node);
        }
        if (comp.clang_preprocessor_mode == .yes) {
            const emit = base.options.emit orelse return; // -fno-emit-bin
            // TODO: avoid extra link step when it's just 1 object file (the `zig cc -c` case)
            // Until then, we do `lld -r -o output.o input.o` even though the output is the same
            // as the input. For the preprocessing case (`zig cc -E -o foo`) we copy the file
            // to the final location. See also the corresponding TODO in Coff linking.
            const full_out_path = try emit.directory.join(comp.gpa, &[_][]const u8{emit.sub_path});
            defer comp.gpa.free(full_out_path);
            assert(comp.c_object_table.count() == 1);
            const the_key = comp.c_object_table.keys()[0];
            const cached_pp_file_path = the_key.status.success.object_path;
            try fs.cwd().copyFile(cached_pp_file_path, fs.cwd(), full_out_path, .{});
            return;
        }

        const use_lld = build_options.have_llvm and base.options.use_lld;
        if (use_lld and base.options.output_mode == .Lib and base.options.link_mode == .Static) {
            return base.linkAsArchive(comp, prog_node);
        }
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).flush(comp, prog_node),
            .elf => return @fieldParentPtr(Elf, "base", base).flush(comp, prog_node),
            .macho => return @fieldParentPtr(MachO, "base", base).flush(comp, prog_node),
            .c => return @fieldParentPtr(C, "base", base).flush(comp, prog_node),
            .wasm => return @fieldParentPtr(Wasm, "base", base).flush(comp, prog_node),
            .spirv => return @fieldParentPtr(SpirV, "base", base).flush(comp, prog_node),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).flush(comp, prog_node),
            .nvptx => return @fieldParentPtr(NvPtx, "base", base).flush(comp, prog_node),
        }
    }

    /// Commit pending changes and write headers. Works based on `effectiveOutputMode`
    /// rather than final output mode.
    pub fn flushModule(base: *File, comp: *Compilation, prog_node: *std.Progress.Node) FlushError!void {
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).flushModule(comp, prog_node);
        }
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).flushModule(comp, prog_node),
            .elf => return @fieldParentPtr(Elf, "base", base).flushModule(comp, prog_node),
            .macho => return @fieldParentPtr(MachO, "base", base).flushModule(comp, prog_node),
            .c => return @fieldParentPtr(C, "base", base).flushModule(comp, prog_node),
            .wasm => return @fieldParentPtr(Wasm, "base", base).flushModule(comp, prog_node),
            .spirv => return @fieldParentPtr(SpirV, "base", base).flushModule(comp, prog_node),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).flushModule(comp, prog_node),
            .nvptx => return @fieldParentPtr(NvPtx, "base", base).flushModule(comp, prog_node),
        }
    }

    /// Called when a Decl is deleted from the Module.
    pub fn freeDecl(base: *File, decl_index: Module.Decl.Index) void {
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).freeDecl(decl_index);
        }
        switch (base.tag) {
            .coff => @fieldParentPtr(Coff, "base", base).freeDecl(decl_index),
            .elf => @fieldParentPtr(Elf, "base", base).freeDecl(decl_index),
            .macho => @fieldParentPtr(MachO, "base", base).freeDecl(decl_index),
            .c => @fieldParentPtr(C, "base", base).freeDecl(decl_index),
            .wasm => @fieldParentPtr(Wasm, "base", base).freeDecl(decl_index),
            .spirv => @fieldParentPtr(SpirV, "base", base).freeDecl(decl_index),
            .plan9 => @fieldParentPtr(Plan9, "base", base).freeDecl(decl_index),
            .nvptx => @fieldParentPtr(NvPtx, "base", base).freeDecl(decl_index),
        }
    }

    pub fn errorFlags(base: *File) ErrorFlags {
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).error_flags,
            .elf => return @fieldParentPtr(Elf, "base", base).error_flags,
            .macho => return @fieldParentPtr(MachO, "base", base).error_flags,
            .plan9 => return @fieldParentPtr(Plan9, "base", base).error_flags,
            .c => return .{ .no_entry_point_found = false },
            .wasm, .spirv, .nvptx => return ErrorFlags{},
        }
    }

    pub const UpdateDeclExportsError = error{
        OutOfMemory,
        AnalysisFail,
    };

    /// May be called before or after updateDecl, but must be called after
    /// allocateDeclIndexes for any given Decl.
    pub fn updateDeclExports(
        base: *File,
        module: *Module,
        decl_index: Module.Decl.Index,
        exports: []const *Module.Export,
    ) UpdateDeclExportsError!void {
        const decl = module.declPtr(decl_index);
        log.debug("updateDeclExports {*} ({s})", .{ decl, decl.name });
        assert(decl.has_tv);
        if (build_options.only_c) {
            assert(base.tag == .c);
            return @fieldParentPtr(C, "base", base).updateDeclExports(module, decl_index, exports);
        }
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).updateDeclExports(module, decl_index, exports),
            .elf => return @fieldParentPtr(Elf, "base", base).updateDeclExports(module, decl_index, exports),
            .macho => return @fieldParentPtr(MachO, "base", base).updateDeclExports(module, decl_index, exports),
            .c => return @fieldParentPtr(C, "base", base).updateDeclExports(module, decl_index, exports),
            .wasm => return @fieldParentPtr(Wasm, "base", base).updateDeclExports(module, decl_index, exports),
            .spirv => return @fieldParentPtr(SpirV, "base", base).updateDeclExports(module, decl_index, exports),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).updateDeclExports(module, decl_index, exports),
            .nvptx => return @fieldParentPtr(NvPtx, "base", base).updateDeclExports(module, decl_index, exports),
        }
    }

    pub const RelocInfo = struct {
        parent_atom_index: u32,
        offset: u64,
        addend: u32,
    };

    /// Get allocated `Decl`'s address in virtual memory.
    /// The linker is passed information about the containing atom, `parent_atom_index`, and offset within it's
    /// memory buffer, `offset`, so that it can make a note of potential relocation sites, should the
    /// `Decl`'s address was not yet resolved, or the containing atom gets moved in virtual memory.
    pub fn getDeclVAddr(base: *File, decl_index: Module.Decl.Index, reloc_info: RelocInfo) !u64 {
        if (build_options.only_c) unreachable;
        switch (base.tag) {
            .coff => return @fieldParentPtr(Coff, "base", base).getDeclVAddr(decl_index, reloc_info),
            .elf => return @fieldParentPtr(Elf, "base", base).getDeclVAddr(decl_index, reloc_info),
            .macho => return @fieldParentPtr(MachO, "base", base).getDeclVAddr(decl_index, reloc_info),
            .plan9 => return @fieldParentPtr(Plan9, "base", base).getDeclVAddr(decl_index, reloc_info),
            .c => unreachable,
            .wasm => return @fieldParentPtr(Wasm, "base", base).getDeclVAddr(decl_index, reloc_info),
            .spirv => unreachable,
            .nvptx => unreachable,
        }
    }

    /// This function is called by the frontend before flush(). It communicates that
    /// `options.bin_file.emit` directory needs to be renamed from
    /// `[zig-cache]/tmp/[random]` to `[zig-cache]/o/[digest]`.
    /// The frontend would like to simply perform a file system rename, however,
    /// some linker backends care about the file paths of the objects they are linking.
    /// So this function call tells linker backends to rename the paths of object files
    /// to observe the new directory path.
    /// Linker backends which do not have this requirement can fall back to the simple
    /// implementation at the bottom of this function.
    /// This function is only called when CacheMode is `whole`.
    pub fn renameTmpIntoCache(
        base: *File,
        cache_directory: Compilation.Directory,
        tmp_dir_sub_path: []const u8,
        o_sub_path: []const u8,
    ) !void {
        // So far, none of the linker backends need to respond to this event, however,
        // it makes sense that they might want to. So we leave this mechanism here
        // for now. Once the linker backends get more mature, if it turns out this
        // is not needed we can refactor this into having the frontend do the rename
        // directly, and remove this function from link.zig.
        _ = base;
        while (true) {
            if (builtin.os.tag == .windows) {
                // Work around windows `renameW` can't fail with `PathAlreadyExists`
                // See https://github.com/ziglang/zig/issues/8362
                if (cache_directory.handle.access(o_sub_path, .{})) |_| {
                    try cache_directory.handle.deleteTree(o_sub_path);
                    continue;
                } else |err| switch (err) {
                    error.FileNotFound => {},
                    else => |e| return e,
                }
                std.fs.rename(
                    cache_directory.handle,
                    tmp_dir_sub_path,
                    cache_directory.handle,
                    o_sub_path,
                ) catch |err| {
                    log.err("unable to rename cache dir {s} to {s}: {s}", .{ tmp_dir_sub_path, o_sub_path, @errorName(err) });
                    return err;
                };
                break;
            } else {
                std.fs.rename(
                    cache_directory.handle,
                    tmp_dir_sub_path,
                    cache_directory.handle,
                    o_sub_path,
                ) catch |err| switch (err) {
                    error.PathAlreadyExists => {
                        try cache_directory.handle.deleteTree(o_sub_path);
                        continue;
                    },
                    else => |e| return e,
                };
                break;
            }
        }
    }

    pub fn linkAsArchive(base: *File, comp: *Compilation, prog_node: *std.Progress.Node) FlushError!void {
        const tracy = trace(@src());
        defer tracy.end();

        var arena_allocator = std.heap.ArenaAllocator.init(base.allocator);
        defer arena_allocator.deinit();
        const arena = arena_allocator.allocator();

        const directory = base.options.emit.?.directory; // Just an alias to make it shorter to type.
        const full_out_path = try directory.join(arena, &[_][]const u8{base.options.emit.?.sub_path});
        const full_out_path_z = try arena.dupeZ(u8, full_out_path);

        // If there is no Zig code to compile, then we should skip flushing the output file
        // because it will not be part of the linker line anyway.
        const module_obj_path: ?[]const u8 = if (base.options.module != null) blk: {
            try base.flushModule(comp, prog_node);

            const dirname = fs.path.dirname(full_out_path_z) orelse ".";
            break :blk try fs.path.join(arena, &.{ dirname, base.intermediary_basename.? });
        } else null;

        log.debug("module_obj_path={s}", .{if (module_obj_path) |s| s else "(null)"});

        const compiler_rt_path: ?[]const u8 = if (base.options.include_compiler_rt)
            comp.compiler_rt_obj.?.full_object_path
        else
            null;

        // This function follows the same pattern as link.Elf.linkWithLLD so if you want some
        // insight as to what's going on here you can read that function body which is more
        // well-commented.

        const id_symlink_basename = "llvm-ar.id";

        var man: Cache.Manifest = undefined;
        defer if (!base.options.disable_lld_caching) man.deinit();

        var digest: [Cache.hex_digest_len]u8 = undefined;

        if (!base.options.disable_lld_caching) {
            man = comp.cache_parent.obtain();

            // We are about to obtain this lock, so here we give other processes a chance first.
            base.releaseLock();

            for (base.options.objects) |obj| {
                _ = try man.addFile(obj.path, null);
                man.hash.add(obj.must_link);
            }
            for (comp.c_object_table.keys()) |key| {
                _ = try man.addFile(key.status.success.object_path, null);
            }
            try man.addOptionalFile(module_obj_path);
            try man.addOptionalFile(compiler_rt_path);

            // We don't actually care whether it's a cache hit or miss; we just need the digest and the lock.
            _ = try man.hit();
            digest = man.final();

            var prev_digest_buf: [digest.len]u8 = undefined;
            const prev_digest: []u8 = Cache.readSmallFile(
                directory.handle,
                id_symlink_basename,
                &prev_digest_buf,
            ) catch |err| b: {
                log.debug("archive new_digest={s} readFile error: {s}", .{ std.fmt.fmtSliceHexLower(&digest), @errorName(err) });
                break :b prev_digest_buf[0..0];
            };
            if (mem.eql(u8, prev_digest, &digest)) {
                log.debug("archive digest={s} match - skipping invocation", .{std.fmt.fmtSliceHexLower(&digest)});
                base.lock = man.toOwnedLock();
                return;
            }

            // We are about to change the output file to be different, so we invalidate the build hash now.
            directory.handle.deleteFile(id_symlink_basename) catch |err| switch (err) {
                error.FileNotFound => {},
                else => |e| return e,
            };
        }

        const num_object_files = base.options.objects.len + comp.c_object_table.count() + 2;
        var object_files = try std.ArrayList([*:0]const u8).initCapacity(base.allocator, num_object_files);
        defer object_files.deinit();

        for (base.options.objects) |obj| {
            object_files.appendAssumeCapacity(try arena.dupeZ(u8, obj.path));
        }
        for (comp.c_object_table.keys()) |key| {
            object_files.appendAssumeCapacity(try arena.dupeZ(u8, key.status.success.object_path));
        }
        if (module_obj_path) |p| {
            object_files.appendAssumeCapacity(try arena.dupeZ(u8, p));
        }
        if (compiler_rt_path) |p| {
            object_files.appendAssumeCapacity(try arena.dupeZ(u8, p));
        }

        if (base.options.verbose_link) {
            std.debug.print("ar rcs {s}", .{full_out_path_z});
            for (object_files.items) |arg| {
                std.debug.print(" {s}", .{arg});
            }
            std.debug.print("\n", .{});
        }

        const llvm_bindings = @import("codegen/llvm/bindings.zig");
        const llvm = @import("codegen/llvm.zig");
        const os_tag = llvm.targetOs(base.options.target.os.tag);
        const bad = llvm_bindings.WriteArchive(full_out_path_z, object_files.items.ptr, object_files.items.len, os_tag);
        if (bad) return error.UnableToWriteArchive;

        if (!base.options.disable_lld_caching) {
            Cache.writeSmallFile(directory.handle, id_symlink_basename, &digest) catch |err| {
                log.warn("failed to save archive hash digest file: {s}", .{@errorName(err)});
            };

            man.writeManifest() catch |err| {
                log.warn("failed to write cache manifest when archiving: {s}", .{@errorName(err)});
            };

            base.lock = man.toOwnedLock();
        }
    }

    pub const Tag = enum {
        coff,
        elf,
        macho,
        c,
        wasm,
        spirv,
        plan9,
        nvptx,
    };

    pub const ErrorFlags = struct {
        no_entry_point_found: bool = false,
        missing_libc: bool = false,
    };

    pub const C = @import("link/C.zig");
    pub const Coff = @import("link/Coff.zig");
    pub const Plan9 = @import("link/Plan9.zig");
    pub const Elf = @import("link/Elf.zig");
    pub const MachO = @import("link/MachO.zig");
    pub const SpirV = @import("link/SpirV.zig");
    pub const Wasm = @import("link/Wasm.zig");
    pub const NvPtx = @import("link/NvPtx.zig");
    pub const Dwarf = @import("link/Dwarf.zig");
};

pub fn determineMode(options: Options) fs.File.Mode {
    // On common systems with a 0o022 umask, 0o777 will still result in a file created
    // with 0o755 permissions, but it works appropriately if the system is configured
    // more leniently. As another data point, C's fopen seems to open files with the
    // 666 mode.
    const executable_mode = if (builtin.target.os.tag == .windows) 0 else 0o777;
    switch (options.effectiveOutputMode()) {
        .Lib => return switch (options.link_mode) {
            .Dynamic => executable_mode,
            .Static => fs.File.default_mode,
        },
        .Exe => return executable_mode,
        .Obj => return fs.File.default_mode,
    }
}