Commit 7148b31956911d5d5496900bf564ca5212bf199b | rust

author	bors <bors@rust-lang.org> 2026-07-05 12:04:25 UTC
committer	bors <bors@rust-lang.org> 2026-07-05 12:04:25 UTC
log	7148b31956911d5d5496900bf564ca5212bf199b
tree	ba776dcb2b9a2b61dbc40d99b4d8d89dc8282499
parent	4eb62535fc12dd1a63fd43a4173e224e79313c4d
parent	7c1d8b8204b199060ee31b3c684dd64185a51467

Auto merge of #158169 - Kobzol:fix-cc-rs-flag-if-supported, r=bjorn3

Fix debuginfo compression in bootstrap



Found through https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/weird.20code.20in.20fill_target_compiler/with/604588655.

This PR solves a few issues with debuginfo compression in bootstrap.

The main issue was that debuginfo compression through the `-gz` flag wasn't enabled, by mistake.

When `cc-rs` checks if a compiler flag is supported, it tries to read `out_dir` to generate the source file in. However, when this option is not set, then the check silently fails and the flag is considered to be unsupported. Since we didn't set `out_dir`, all such added flags were simply ignored.

Normally, it reads `OUT_DIR`, which is fine if `cc-rs` is used within a build script. But if it is used elsewhere, then this is a pretty gnarly footgun in `cc-rs`, because the failure is [completely silent](https://github.com/rust-lang/cc-rs/blob/main/src/lib.rs#L1483).  CC @madsmtm or @NobodyXu in case you have thoughts on that :)

After that was fixed, I had to change the used compression flag from `-gz` to `--compress-debug-sections`, to support both BFD and LLD linkers.

And to solve it properly, and allow `dist` CI jobs to configure debuginfo compression for all targets that they build, I added a new bootstrap option to configure debuginfo compression.

I wanted the flag to be configurable both globally and per target. At the same time, the flag applies both to C/C++ and Rust. We currently don't have such config area in `bootstrap.toml`, and `[build]` didn't seem like the right place, so I shoved it into `[rust]` (while documenting that it also applies to C/C++).

r? @bjorn3

try-job: dist-x86_64-msvc
try-job: dist-x86_64-apple
try-job: dist-x86_64-linux
try-job: dist-various-1
try-job: dist-various-2

13 files changed, 134 insertions(+), 20 deletions(-)

bootstrap.example.toml+16

...	...	@@ -697,6 +697,14 @@
697	697	# FIXME(#61117): Some tests fail when this option is enabled.
698	698	#rust.debuginfo-level-tests = 0
699	699
	700	# Compress debuginfo of Rust and C/C++ code.
	701	# Currently, this only works on Linux.
	702	# Valid options:
	703	# - "off" or false: disable compression
	704	# - true: compress debuginfo with the default compression method (currently zlib)
	705	# - "zlib": compress debuginfo with zlib
	706	#rust.compress-debuginfo = "off"
	707
700	708	# Should rustc and the standard library be built with split debuginfo? Default
701	709	# is platform dependent.
702	710	#
...	...	@@ -1019,6 +1027,14 @@
1019	1027	# and enabling it causes issues.
1020	1028	#split-debuginfo = if linux \|\| windows-gnu { off } else if windows-msvc { packed } else if apple { unpacked }
1021	1029
	1030	# Compress debuginfo for Rust and C/C++ code of this target.
	1031	# Currently, this only works on Linux.
	1032	# Valid options:
	1033	# - "off" or false: disable compression
	1034	# - true: compress debuginfo with the default compression method (currently zlib)
	1035	# - "zlib": compress debuginfo with zlib
	1036	#compress-debuginfo = "off"
	1037
1022	1038	# Path to the `llvm-config` binary of the installation of a custom LLVM to link
1023	1039	# against. Note that if this is specified we don't compile LLVM at all for this
1024	1040	# target.

src/bootstrap/defaults/bootstrap.dist.toml+2

...	...	@@ -26,6 +26,8 @@ download-rustc = false
26	26	llvm-bitcode-linker = true
27	27	# Required to make builds reproducible.
28	28	remap-debuginfo = true
	29	# Compress debuginfo in generated artifacts to reduce their size
	30	compress-debuginfo = "zlib"
29	31
30	32	[dist]
31	33	# Use better compression when preparing tarballs.

src/bootstrap/src/core/builder/cargo.rs+18-3

...	...	@@ -5,8 +5,8 @@ use std::path::{Path, PathBuf};
5	5	use super::{Builder, Kind};
6	6	use crate::core::build_steps::test;
7	7	use crate::core::build_steps::tool::SourceType;
8		use crate::core::config::SplitDebuginfo;
9	8	use crate::core::config::flags::Color;
	9	use crate::core::config::{CompressDebuginfo, SplitDebuginfo};
10	10	use crate::utils::build_stamp;
11	11	use crate::utils::helpers::{self, LldThreads, check_cfg_arg, linker_flags};
12	12	use crate::{
...	...	@@ -348,8 +348,23 @@ impl Cargo {
348	348	self.rustdocflags.arg(&arg);
349	349	}
350	350
351		if !builder.config.dry_run() && builder.cc[&target].args().iter().any(\|arg\| arg == "-gz") {
352		self.rustflags.arg("-Clink-arg=-gz");
	351	match builder.config.compress_debuginfo(target) {
	352	CompressDebuginfo::Zlib => {
	353	// Do not enable Zlib compression on:
	354	// - Windows, because MSVC/PDB doesn't support it
	355	// - macOS, because its linker doesn't know the flag
	356	if !self.target.is_windows() && !self.target.is_apple() {
	357	// If we link through cc, we need the -Wl prefix.
	358	// If we don't, then we must not add it, because the linker wouldn't
	359	// understand it.
	360	if helpers::use_host_linker(target) {
	361	self.rustflags.arg("-Clink-arg=-Wl,--compress-debug-sections=zlib");
	362	} else {
	363	self.rustflags.arg("-Clink-arg=--compress-debug-sections=zlib");
	364	}
	365	}
	366	}
	367	CompressDebuginfo::Off => {}
353	368	}
354	369
355	370	// Ignore linker warnings for now. These are complicated to fix and don't affect the build.

src/bootstrap/src/core/config/config.rs+12-2

...	...	@@ -49,8 +49,8 @@ use crate::core::config::toml::target::{
49	49	DefaultLinuxLinkerOverride, Target, TomlTarget, default_linux_linker_overrides,
50	50	};
51	51	use crate::core::config::{
52		CompilerBuiltins, DebuginfoLevel, DryRun, GccCiMode, LlvmLibunwind, Merge, ReplaceOpt,
53		RustcLto, SplitDebuginfo, StringOrBool, threads_from_config,
	52	CompilerBuiltins, CompressDebuginfo, DebuginfoLevel, DryRun, GccCiMode, LlvmLibunwind, Merge,
	53	ReplaceOpt, RustcLto, SplitDebuginfo, StringOrBool, threads_from_config,
54	54	};
55	55	use crate::core::download::{
56	56	DownloadContext, download_beta_toolchain, is_download_ci_available, maybe_download_rustfmt,
...	...	@@ -210,6 +210,7 @@ pub struct Config {
210	210	pub rust_debuginfo_level_std: DebuginfoLevel,
211	211	pub rust_debuginfo_level_tools: DebuginfoLevel,
212	212	pub rust_debuginfo_level_tests: DebuginfoLevel,
	213	pub rust_compress_debuginfo: CompressDebuginfo,
213	214	pub rust_rpath: bool,
214	215	pub rust_strip: bool,
215	216	pub rust_frame_pointers: bool,
...	...	@@ -550,6 +551,7 @@ impl Config {
550	551	debuginfo_level_std: rust_debuginfo_level_std,
551	552	debuginfo_level_tools: rust_debuginfo_level_tools,
552	553	debuginfo_level_tests: rust_debuginfo_level_tests,
	554	compress_debuginfo: rust_compress_debuginfo,
553	555	backtrace: rust_backtrace,
554	556	incremental: rust_incremental,
555	557	randomize_layout: rust_randomize_layout,
...	...	@@ -1471,6 +1473,7 @@ NOTE: Please add `--stage 2` to your command line, or if you're sure you want to
1471	1473	.unwrap_or(vec![CodegenBackendKind::Llvm]),
1472	1474	rust_codegen_units: rust_codegen_units.map(threads_from_config),
1473	1475	rust_codegen_units_std: rust_codegen_units_std.map(threads_from_config),
	1476	rust_compress_debuginfo: rust_compress_debuginfo.unwrap_or_default(),
1474	1477	rust_debug_logging: rust_debug_logging
1475	1478	.or(rust_rustc_debug_assertions)
1476	1479	.unwrap_or(rust_debug == Some(true)),
...	...	@@ -1927,6 +1930,13 @@ NOTE: Please add `--stage 2` to your command line, or if you're sure you want to
1927	1930	.unwrap_or_else(\|\| SplitDebuginfo::default_for_platform(target))
1928	1931	}
1929	1932
	1933	pub fn compress_debuginfo(&self, target: TargetSelection) -> CompressDebuginfo {
	1934	self.target_config
	1935	.get(&target)
	1936	.and_then(\|t\| t.compress_debuginfo)
	1937	.unwrap_or(self.rust_compress_debuginfo)
	1938	}
	1939
1930	1940	/// Checks if the given target is the same as the host target.
1931	1941	pub fn is_host_target(&self, target: TargetSelection) -> bool {
1932	1942	self.host_target == target

src/bootstrap/src/core/config/mod.rs+48

...	...	@@ -32,6 +32,7 @@ use std::path::PathBuf;
32	32
33	33	use build_helper::exit;
34	34	pub use config::*;
	35	use serde::de::Unexpected;
35	36	use serde::{Deserialize, Deserializer};
36	37	use serde_derive::Deserialize;
37	38	pub use target_selection::TargetSelection;
...	...	@@ -378,6 +379,53 @@ impl std::str::FromStr for SplitDebuginfo {
378	379	}
379	380	}
380	381
	382	#[derive(Debug, Default, Copy, Clone, PartialEq, Eq, Hash)]
	383	pub enum CompressDebuginfo {
	384	Zlib,
	385	#[default]
	386	Off,
	387	}
	388
	389	impl CompressDebuginfo {
	390	fn default_on() -> Self {
	391	Self::Zlib
	392	}
	393	}
	394
	395	impl std::str::FromStr for CompressDebuginfo {
	396	type Err = ();
	397
	398	fn from_str(s: &str) -> Result<Self, Self::Err> {
	399	match s {
	400	"zlib" => Ok(CompressDebuginfo::Zlib),
	401	"off" => Ok(CompressDebuginfo::Off),
	402	_ => Err(()),
	403	}
	404	}
	405	}
	406
	407	impl<'de> Deserialize<'de> for CompressDebuginfo {
	408	fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
	409	where
	410	D: Deserializer<'de>,
	411	{
	412	use serde::de::Error;
	413
	414	Ok(match Deserialize::deserialize(deserializer)? {
	415	StringOrBool::Bool(value) => {
	416	if value {
	417	CompressDebuginfo::default_on()
	418	} else {
	419	CompressDebuginfo::Off
	420	}
	421	}
	422	StringOrBool::String(value) => CompressDebuginfo::from_str(&value).map_err(\|_\| {
	423	D::Error::invalid_value(Unexpected::Str(&value), &"`zlib` or `off`")
	424	})?,
	425	})
	426	}
	427	}
	428
381	429	/// Describes how to handle conflicts in merging two `TomlConfig`
382	430	#[derive(Copy, Clone, Debug)]
383	431	pub enum ReplaceOpt {

src/bootstrap/src/core/config/target_selection.rs+4

...	...	@@ -86,6 +86,10 @@ impl TargetSelection {
86	86	self.contains("windows")
87	87	}
88	88
	89	pub fn is_apple(&self) -> bool {
	90	self.contains("apple")
	91	}
	92
89	93	pub fn is_windows_gnu(&self) -> bool {
90	94	self.ends_with("windows-gnu")
91	95	}

src/bootstrap/src/core/config/toml/rust.rs+4-1

...	...	@@ -5,7 +5,7 @@ use build_helper::ci::CiEnv;
5	5	use serde::{Deserialize, Deserializer};
6	6
7	7	use crate::core::config::toml::TomlConfig;
8		use crate::core::config::{DebuginfoLevel, Merge, ReplaceOpt, StringOrBool};
	8	use crate::core::config::{CompressDebuginfo, DebuginfoLevel, Merge, ReplaceOpt, StringOrBool};
9	9	use crate::{BTreeSet, CodegenBackendKind, HashSet, PathBuf, TargetSelection, define_config, exit};
10	10
11	11	define_config! {
...	...	@@ -28,6 +28,7 @@ define_config! {
28	28	debuginfo_level_std: Option<DebuginfoLevel> = "debuginfo-level-std",
29	29	debuginfo_level_tools: Option<DebuginfoLevel> = "debuginfo-level-tools",
30	30	debuginfo_level_tests: Option<DebuginfoLevel> = "debuginfo-level-tests",
	31	compress_debuginfo: Option<CompressDebuginfo> = "compress-debuginfo",
31	32	backtrace: Option<bool> = "backtrace",
32	33	incremental: Option<bool> = "incremental",
33	34	default_linker: Option<String> = "default-linker",
...	...	@@ -322,6 +323,7 @@ pub fn check_incompatible_options_for_ci_rustc(
322	323	randomize_layout,
323	324	debug_logging,
324	325	debuginfo_level_rustc,
	326	compress_debuginfo,
325	327	llvm_tools,
326	328	llvm_bitcode_linker,
327	329	stack_protector,
...	...	@@ -389,6 +391,7 @@ pub fn check_incompatible_options_for_ci_rustc(
389	391
390	392	err!(current_rust_config.optimize, optimize, "rust");
391	393	err!(current_rust_config.randomize_layout, randomize_layout, "rust");
	394	err!(current_rust_config.compress_debuginfo, compress_debuginfo, "rust");
392	395	err!(current_rust_config.debug_logging, debug_logging, "rust");
393	396	err!(current_rust_config.debuginfo_level_rustc, debuginfo_level_rustc, "rust");
394	397	err!(current_rust_config.rpath, rpath, "rust");

src/bootstrap/src/core/config/toml/target.rs+3-1

...	...	@@ -15,7 +15,8 @@ use serde::de::Error;
15	15	use serde::{Deserialize, Deserializer};
16	16
17	17	use crate::core::config::{
18		CompilerBuiltins, LlvmLibunwind, Merge, ReplaceOpt, SplitDebuginfo, StringOrBool,
	18	CompilerBuiltins, CompressDebuginfo, LlvmLibunwind, Merge, ReplaceOpt, SplitDebuginfo,
	19	StringOrBool,
19	20	};
20	21	use crate::{CodegenBackendKind, HashSet, PathBuf, define_config, exit};
21	22
...	...	@@ -68,6 +69,7 @@ pub struct Target {
68	69	pub default_linker_linux_override: DefaultLinuxLinkerOverride,
69	70	pub linker: Option<PathBuf>,
70	71	pub split_debuginfo: Option<SplitDebuginfo>,
	72	pub compress_debuginfo: Option<CompressDebuginfo>,
71	73	pub sanitizers: Option<bool>,
72	74	pub profiler: Option<StringOrBool>,
73	75	pub rpath: Option<bool>,

src/bootstrap/src/utils/cc_detect.rs+17-11

...	...	@@ -25,7 +25,7 @@ use std::collections::HashSet;
25	25	use std::iter;
26	26	use std::path::{Path, PathBuf};
27	27
28		use crate::core::config::TargetSelection;
	28	use crate::core::config::{CompressDebuginfo, TargetSelection};
29	29	use crate::utils::exec::{BootstrapCommand, command};
30	30	use crate::{Build, CLang, GitRepo};
31	31
...	...	@@ -36,10 +36,18 @@ fn new_cc_build(build: &Build, target: TargetSelection) -> cc::Build {
36	36	.opt_level(2)
37	37	.warnings(false)
38	38	.debug(false)
39		// Compress debuginfo
40		.flag_if_supported("-gz")
	39	// We have to configure out_dir, otherwise flag_if_supported will not work
	40	.out_dir(build.tempdir().join("cc-rs-out-dir"))
41	41	.target(&target.triple)
42	42	.host(&build.host_target.triple);
	43
	44	match build.config.compress_debuginfo(target) {
	45	CompressDebuginfo::Zlib => {
	46	cfg.flag_if_supported("-gz");
	47	}
	48	CompressDebuginfo::Off => {}
	49	}
	50
43	51	match build.crt_static(target) {
44	52	Some(a) => {
45	53	cfg.static_crt(a);
...	...	@@ -100,17 +108,15 @@ pub fn fill_target_compiler(build: &mut Build, target: TargetSelection) {
100	108	let config = build.config.target_config.get(&target);
101	109	if let Some(cc) = config
102	110	.and_then(\|c\| c.cc.clone())
103		.or_else(\|\| default_compiler(&mut cfg, Language::C, target, build))
	111	.or_else(\|\| default_compiler(&cfg, Language::C, target, build))
104	112	{
105	113	cfg.compiler(cc);
106	114	}
107	115
108	116	let compiler = cfg.get_compiler();
109		let ar = if let ar @ Some(..) = config.and_then(\|c\| c.ar.clone()) {
110		ar
111		} else {
112		cfg.try_get_archiver().map(\|c\| PathBuf::from(c.get_program())).ok()
113		};
	117	let ar = config
	118	.and_then(\|c\| c.ar.clone())
	119	.or_else(\|\| cfg.try_get_archiver().map(\|c\| PathBuf::from(c.get_program())).ok());
114	120
115	121	build.cc.insert(target, compiler.clone());
116	122	let mut cflags = build.cc_handled_clags(target, CLang::C);
...	...	@@ -122,7 +128,7 @@ pub fn fill_target_compiler(build: &mut Build, target: TargetSelection) {
122	128	cfg.cpp(true);
123	129	let cxx_configured = if let Some(cxx) = config
124	130	.and_then(\|c\| c.cxx.clone())
125		.or_else(\|\| default_compiler(&mut cfg, Language::CPlusPlus, target, build))
	131	.or_else(\|\| default_compiler(&cfg, Language::CPlusPlus, target, build))
126	132	{
127	133	cfg.compiler(cxx);
128	134	true
...	...	@@ -158,7 +164,7 @@ pub fn fill_target_compiler(build: &mut Build, target: TargetSelection) {
158	164	/// Determines the default compiler for a given target and language when not explicitly
159	165	/// configured in `bootstrap.toml`.
160	166	fn default_compiler(
161		cfg: &mut cc::Build,
	167	cfg: &cc::Build,
162	168	compiler: Language,
163	169	target: TargetSelection,
164	170	build: &Build,

src/bootstrap/src/utils/cc_detect/tests.rs+2-2

...	...	@@ -86,7 +86,7 @@ fn test_default_compiler_wasi() {
86	86	build.wasi_sdk_path = Some(wasi_sdk.clone());
87	87
88	88	let mut cfg = cc::Build::new();
89		if let Some(result) = default_compiler(&mut cfg, Language::C, target.clone(), &build) {
	89	if let Some(result) = default_compiler(&cfg, Language::C, target.clone(), &build) {
90	90	let expected = {
91	91	let compiler = format!("{}-clang", target.triple);
92	92	wasi_sdk.join("bin").join(compiler)
...	...	@@ -105,7 +105,7 @@ fn test_default_compiler_fallback() {
105	105	let build = Build::new(config);
106	106	let target = TargetSelection::from_user("x86_64-unknown-linux-gnu");
107	107	let mut cfg = cc::Build::new();
108		let result = default_compiler(&mut cfg, Language::C, target, &build);
	108	let result = default_compiler(&cfg, Language::C, target, &build);
109	109	assert!(result.is_none(), "default_compiler should return None for generic targets");
110	110	}
111	111

src/bootstrap/src/utils/change_tracker.rs+5

...	...	@@ -631,4 +631,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
631	631	severity: ChangeSeverity::Info,
632	632	summary: "New `--verbose-run-make-subprocess-output` flag for `x.py test` (defaults to true). Set `--verbose-run-make-subprocess-output=false` to suppress verbose subprocess output for passing run-make tests when using `--no-capture`.",
633	633	},
	634	ChangeInfo {
	635	change_id: 158169,
	636	severity: ChangeSeverity::Info,
	637	summary: "New option `rust.compress-debuginfo` allows configuring whether Rust and C/C++ debuginfo should be compressed.",
	638	},
634	639	];

src/ci/docker/host-x86_64/x86_64-gnu-distcheck/Dockerfile+1

...	...	@@ -28,6 +28,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
28	28	xz-utils \
29	29	libssl-dev \
30	30	pkg-config \
	31	zlib1g-dev \
31	32	&& rm -rf /var/lib/apt/lists/*
32	33
33	34	COPY scripts/sccache.sh /scripts/

src/ci/run.sh+2

...	...	@@ -137,6 +137,8 @@ if [ "$DEPLOY$DEPLOY_ALT" = "1" ]; then
137	137	fi
138	138	else
139	139	RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.remap-debuginfo=false"
	140	# No need to compress debuginfo for tests, and we do not want to depend on zlib
	141	RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.compress-debuginfo=off"
140	142
141	143	# We almost always want debug assertions enabled, but sometimes this takes too
142	144	# long for too little benefit, so we just turn them off.