--remap-path-prefix not remapping out_dir in debug info on Wasm

[alecmocatta]

I'm seeing an un-remapped path in a Wasm bin compiled with --target=wasm32-unknown-unknown --release debug = 1 --remap-path-prefix=$CARGO_MANIFEST_DIR= on nightly-2021-01-02. Here's a snippet of it and a couple of preceding strings that help contextualise:

\0clang LLVM (rustc version 1.51.0-nightly (17eec1433 2021-01-01))\0frontend/src/lib.rs\0/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps\0

It looks like it's the out_dir that's not getting remapped:

rust/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

Lines 970 to 1109 in dfdfaa1

	pub fn compile_unit_metadata(
	tcx: TyCtxt<'_>,
	codegen_unit_name: &str,
	debug_context: &CrateDebugContext<'ll, '_>,
	) -> &'ll DIDescriptor {
	let mut name_in_debuginfo = match tcx.sess.local_crate_source_file {
	Some(ref path) => path.clone(),
	None => PathBuf::from(&*tcx.crate_name(LOCAL_CRATE).as_str()),
	};
	// The OSX linker has an idiosyncrasy where it will ignore some debuginfo
	// if multiple object files with the same `DW_AT_name` are linked together.
	// As a workaround we generate unique names for each object file. Those do
	// not correspond to an actual source file but that should be harmless.
	if tcx.sess.target.is_like_osx {
	name_in_debuginfo.push("@");
	name_in_debuginfo.push(codegen_unit_name);
	}
	debug!("compile_unit_metadata: {:?}", name_in_debuginfo);
	let rustc_producer =
	format!("rustc version {}", option_env!("CFG_VERSION").expect("CFG_VERSION"),);
	// FIXME(#41252) Remove "clang LLVM" if we can get GDB and LLVM to play nice.
	let producer = format!("clang LLVM ({})", rustc_producer);
	let name_in_debuginfo = name_in_debuginfo.to_string_lossy();
	let flags = "\0";
	let out_dir = &tcx.output_filenames(LOCAL_CRATE).out_directory;
	let split_name = tcx
	.output_filenames(LOCAL_CRATE)
	.split_dwarf_filename(tcx.sess.opts.debugging_opts.split_dwarf, Some(codegen_unit_name))
	.unwrap_or_default();
	let out_dir = out_dir.to_str().unwrap();
	let split_name = split_name.to_str().unwrap();
	// FIXME(#60020):
	//
	// This should actually be
	//
	// let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
	//
	// That is, we should set LLVM's emission kind to `LineTablesOnly` if
	// we are compiling with "limited" debuginfo. However, some of the
	// existing tools relied on slightly more debuginfo being generated than
	// would be the case with `LineTablesOnly`, and we did not want to break
	// these tools in a "drive-by fix", without a good idea or plan about
	// what limited debuginfo should exactly look like. So for now we keep
	// the emission kind as `FullDebug`.
	//
	// See https://github.com/rust-lang/rust/issues/60020 for details.
	let kind = DebugEmissionKind::FullDebug;
	assert!(tcx.sess.opts.debuginfo != DebugInfo::None);
	unsafe {
	let file_metadata = llvm::LLVMRustDIBuilderCreateFile(
	debug_context.builder,
	name_in_debuginfo.as_ptr().cast(),
	name_in_debuginfo.len(),
	out_dir.as_ptr().cast(),
	out_dir.len(),
	llvm::ChecksumKind::None,
	ptr::null(),
	0,
	);
	let unit_metadata = llvm::LLVMRustDIBuilderCreateCompileUnit(
	debug_context.builder,
	DW_LANG_RUST,
	file_metadata,
	producer.as_ptr().cast(),
	producer.len(),
	tcx.sess.opts.optimize != config::OptLevel::No,
	flags.as_ptr().cast(),
	0,
	split_name.as_ptr().cast(),
	split_name.len(),
	kind,
	0,
	tcx.sess.opts.debugging_opts.split_dwarf_inlining,
	);
	if tcx.sess.opts.debugging_opts.profile {
	let cu_desc_metadata =
	llvm::LLVMRustMetadataAsValue(debug_context.llcontext, unit_metadata);
	let default_gcda_path = &tcx.output_filenames(LOCAL_CRATE).with_extension("gcda");
	let gcda_path =
	tcx.sess.opts.debugging_opts.profile_emit.as_ref().unwrap_or(default_gcda_path);
	let gcov_cu_info = [
	path_to_mdstring(
	debug_context.llcontext,
	&tcx.output_filenames(LOCAL_CRATE).with_extension("gcno"),
	),
	path_to_mdstring(debug_context.llcontext, &gcda_path),
	cu_desc_metadata,
	];
	let gcov_metadata = llvm::LLVMMDNodeInContext(
	debug_context.llcontext,
	gcov_cu_info.as_ptr(),
	gcov_cu_info.len() as c_uint,
	);
	let llvm_gcov_ident = const_cstr!("llvm.gcov");
	llvm::LLVMAddNamedMetadataOperand(
	debug_context.llmod,
	llvm_gcov_ident.as_ptr(),
	gcov_metadata,
	);
	}
	// Insert `llvm.ident` metadata on the wasm32 targets since that will
	// get hooked up to the "producer" sections `processed-by` information.
	if tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
	let name_metadata = llvm::LLVMMDStringInContext(
	debug_context.llcontext,
	rustc_producer.as_ptr().cast(),
	rustc_producer.as_bytes().len() as c_uint,
	);
	llvm::LLVMAddNamedMetadataOperand(
	debug_context.llmod,
	const_cstr!("llvm.ident").as_ptr(),
	llvm::LLVMMDNodeInContext(debug_context.llcontext, &name_metadata, 1),
	);
	}
	return unit_metadata;
	};
	fn path_to_mdstring(llcx: &'ll llvm::Context, path: &Path) -> &'ll Value {
	let path_str = path_to_c_string(path);
	unsafe {
	llvm::LLVMMDStringInContext(
	llcx,
	path_str.as_ptr(),
	path_str.as_bytes().len() as c_uint,
	)
	}
	}
	}

[nagisa]

Are you passing $CARGO_MANIFEST_DIR as an argument verbatim (that probably won't work, rustc won't expand arguments)? Can you post the arguments that the invocation of rustc receives?

(Doing so may involve suspending the execution of rustc and then obtaining the CLI through operating system; e.g. on Linux via cat /proc/<PID>/cmdline)

[alecmocatta]

RUSTFLAGS='--remap-path-prefix=/Users/alec/Documents/frontend= --remap-path-prefix=/Users/alec/.rustup/toolchains/nightly-x86_64-apple-darwin= --remap-path-prefix=/Users/alec/.cargo/registry/src=' cargo build --package=frontend --lib --target=wasm32-unknown-unknown -Z build-std=std,panic_abort --release --verbose:

rustc --crate-name frontend --edition=2018 frontend/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type cdylib --emit=dep-info,link -C opt-level=3 -C panic=abort -C embed-bitcode=no -C debuginfo=1 -C overflow-checks=on -C metadata=d690439610fd46ff --out-dir /Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps --target wasm32-unknown-unknown -L dependency=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps -L dependency=/Users/alec/Documents/frontend/target/release/deps --extern 'noprelude:alloc=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/liballoc-21064f837a6ce201.rlib' --extern base64=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libbase64-d1417908bb5c991a.rlib --extern borsh=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libborsh-3a9a2179b6181e6f.rlib --extern bytesize=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libbytesize-ff41001dae3d81ae.rlib --extern common=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libcommon-120bd5d92e90e191.rlib --extern 'noprelude:compiler_builtins=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libcompiler_builtins-cc4855d60cdc44b7.rlib' --extern 'noprelude:core=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libcore-4ca9d146743d88a5.rlib' --extern derive_new=/Users/alec/Documents/frontend/target/release/deps/libderive_new-0a543881a2243fda.dylib --extern either=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libeither-cda7cc04043eb3d8.rlib --extern futures=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libfutures-7fb6fe532f8cdb65.rlib --extern futures_intrusive=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libfutures_intrusive-ec48330797918ba3.rlib --extern instant=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libinstant-8208dddaac005592.rlib --extern js_sys=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libjs_sys-000cf2ac132253e4.rlib --extern maplit=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libmaplit-69a523e37d42b692.rlib --extern num=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libnum-f3858087148fee1b.rlib --extern 'noprelude:panic_abort=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpanic_abort-6540aba0ce5a9639.rlib' --extern 'noprelude:panic_unwind=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpanic_unwind-72b206be10100e2c.rlib' --extern pin_cell=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpin_cell-a19be411f419a79a.rlib --extern pin_project=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpin_project-88db610adffc8c4d.rlib --extern pin_weak=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpin_weak-a31cc3784bfeaa2a.rlib --extern 'noprelude:proc_macro=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libproc_macro-4786600990539276.rlib' --extern pulldown_cmark=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libpulldown_cmark-b92e78ac485ec452.rlib --extern replace_with=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libreplace_with-2ef477612fd10f0d.rlib --extern 'noprelude:std=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libstd-ead026bacacd2c67.rlib' --extern wasm_bindgen=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libwasm_bindgen-7ae4d872bfb78bb4.rlib --extern wasm_bindgen_futures=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libwasm_bindgen_futures-f94a2d9aa3aa1b5b.rlib --extern wasm_timer=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libwasm_timer-33965abb275568e6.rlib --extern web_sys=/Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps/libweb_sys-827dafb5b53a5b12.rlib -Z unstable-options --remap-path-prefix=/Users/alec/Documents/frontend= --remap-path-prefix=/Users/alec/.rustup/toolchains/nightly-x86_64-apple-darwin= --remap-path-prefix=/Users/alec/.cargo/registry/src=

All other paths are successfully remapped so I'm not sure it's related to the argument getting to rustc? It's literally just /Users/alec/Documents/frontend/target/wasm32-unknown-unknown/release/deps that is not remapped.

[nagisa]

Yeah, I just wanted to make sure it is not something obviously wrong with how arguments get to rustc, especially as you mentioned use of environment variables, that are typically set inside cargo.

[nagisa]

This might be fixed by #82102 as well.

[jyn514]

#82102 was merged, are you still running into this?

[alecmocatta]

Confirmed I'm no longer seeing this bug. Thanks both, closing!