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std.Build: add build-id option #22516

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std.Build: add build-id option #22516

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6 changes: 0 additions & 6 deletions build.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -197,12 +197,6 @@ pub fn build(b: *std.Build) !void {
exe.pie = pie;
exe.entitlements = entitlements;

exe.build_id = b.option(
std.zig.BuildId,
"build-id",
"Request creation of '.note.gnu.build-id' section",
);

if (no_bin) {
b.getInstallStep().dependOn(&exe.step);
} else {
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13 changes: 13 additions & 0 deletions lib/compiler/build_runner.zig
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Expand Up @@ -202,6 +202,15 @@ pub fn main() !void {
next_arg, @errorName(err),
});
};
} else if (mem.eql(u8, arg, "--build-id")) {
builder.build_id = .fast;
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Just out of curiosity, why this default in particular? Is there precedent in other build systems / toolchains?

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@Jan200101 Jan200101 Mar 26, 2025 •
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I copied the handling directly from main.zig to keep it the same across build and build-exe

zig/src/main.zig

Lines 1681 to 1682 in b350049

} else if (mem.eql(u8, arg, "--build-id")) {
build_id = .fast;

gcc and clang use sha1 as the default as it was the first build-id to be implemented, I know that the initial zig implementation had it as a boolean option, either on or off, but I am not sure why fast was chosen specifically.

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Do you happen to know what distros tend to use here?

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Fedora (and I assume anything in the same family) explicitly uses sha1

Arch builds gcc with --enable-linker-build-id which automatically passes --build-id to the linker, implying sha1

it might be best to just remove the default here and to demand that the type is explicit

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Some context: #15459 (comment)

At least according to man ld, that comment is wrong.

I think it would be good to verify what ld and ld.lld do here (hopefully they agree), and then change Zig's default, both here and in src/main.zig, to be the same.

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Some context: #15459 (comment)

At least according to man ld, that comment is wrong.

I think I found the reason for this:

LD defaults to sha1 for ELF and md5 for PE
LDD defaults to sha1 for ELF, forced GUID for the msvc compatible linker and fast for wasm

so as a whole there doesn't appear to be one right default for all platforms

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@alexrp alexrp Mar 26, 2025 •
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That's fun. So in summary, defaults look as follows:

  • Mach-O doesn't seem to have a build ID mechanism.
  • ld, lld, and mold all seem to agree on sha1 for ELF.
  • lld uses fast for WASM (UUID v5 based on xxHash).
  • ld uses md5 for COFF, lld uses a variation on fast (both written as a "GUID").

ELF and WASM can in theory support any style. But the current scheme that linkers use for COFF only allows up to 16 bytes, which means that COFF "can't" support sha1 (20 bytes). That's quite unfortunate.

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Okay, I've argued myself into thinking that fast is a good default because it's consistent (ish) across binary formats.

The only missing piece here is that src/link/Coff.zig needs to pass --build-id to LLD when the style is fast. (LLD does not appear to support other styles for COFF at the moment, even though all the non-sha1 styles could be made to work.) Would you mind making that change?

} else if (mem.startsWith(u8, arg, "--build-id=")) {
const style = arg["--build-id=".len..];
builder.build_id = std.zig.BuildId.parse(style) catch |err| {
fatal("unable to parse --build-id style '{s}': {s}", .{
style, @errorName(err),
});
};
} else if (mem.eql(u8, arg, "--debounce")) {
const next_arg = nextArg(args, &arg_idx) orelse
fatalWithHint("expected u16 after '{s}'", .{arg});
Expand Down Expand Up @@ -1364,6 +1373,10 @@ fn usage(b: *std.Build, out_stream: anytype) !void {
\\ --zig-lib-dir [arg] Override path to Zig lib directory
\\ --build-runner [file] Override path to build runner
\\ --seed [integer] For shuffling dependency traversal order (default: random)
\\ --build-id[=style] At a minor link-time expense, coordinates stripped binaries
\\ fast, uuid, sha1, md5 with debug symbols via a '.note.gnu.build-id' section
\\ 0x[hexstring] Maximum 32 bytes
\\ none (default) Disable build-id
Comment on lines +1376 to +1379
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Suggested change
\\ --build-id[=style] At a minor link-time expense, coordinates stripped binaries
\\ fast, uuid, sha1, md5 with debug symbols via a '.note.gnu.build-id' section
\\ 0x[hexstring] Maximum 32 bytes
\\ none (default) Disable build-id
\\ --build-id[=style] At a minor link-time expense, embeds a build ID in binaries
\\ fast 8-byte non-cryptographic hash (COFF, ELF, WASM)
\\ sha1, tree 20-byte cryptographic hash (ELF, WASM)
\\ md5 16-byte cryptographic hash (ELF)
\\ uuid 16-byte random UUID (ELF, WASM)
\\ 0x[hexstring] Constant ID, maximum 32 bytes (ELF, WASM)
\\ none (default) No build ID

And likewise in src/main.zig?

\\ --debug-log [scope] Enable debugging the compiler
\\ --debug-pkg-config Fail if unknown pkg-config flags encountered
\\ --debug-rt Debug compiler runtime libraries
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2 changes: 2 additions & 0 deletions lib/std/Build.zig
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Expand Up @@ -94,6 +94,8 @@ available_deps: AvailableDeps,

release_mode: ReleaseMode,

build_id: ?std.zig.BuildId = null,

pub const ReleaseMode = enum {
off,
any,
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2 changes: 1 addition & 1 deletion lib/std/Build/Step/Compile.zig
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Expand Up @@ -1681,7 +1681,7 @@ fn getZigArgs(compile: *Compile, fuzz: bool) ![][]const u8 {

try addFlag(&zig_args, "each-lib-rpath", compile.each_lib_rpath);

if (compile.build_id) |build_id| {
if (compile.build_id orelse b.build_id) |build_id| {
try zig_args.append(switch (build_id) {
.hexstring => |hs| b.fmt("--build-id=0x{s}", .{
std.fmt.fmtSliceHexLower(hs.toSlice()),
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