A Firefox developer filed a bug report about Rust symbols not being correctly represented in crash reports:

0	XUL	GeckoCrash	toolkit/xre/nsAppRunner.cpp:5093	context 1	XUL	gkrust_shared::panic_hook	toolkit/library/rust/shared/lib.rs:240	frame_pointer 2	XUL	core::ops::function::Fn::call	src/libcore/ops/function.rs:69	cfi 3	XUL	rust_panic_with_hook	src/libstd/panicking.rs:482	cfi 4	XUL	continue_panic_fmt	src/libstd/panicking.rs:385	cfi 5	XUL	rust_begin_panic	src/libstd/panicking.rs:312	cfi 6	XUL	panic_fmt	src/libcore/panicking.rs:85	cfi 7	XUL	panic	src/libcore/panicking.rs:49	cfi 

The expectation was that, e.g. rust_panic_with_hook would have been std::panicking::rust_panic_with_hook.

We had recently upgraded to Rust 1.34, which led to comparing object files before and after the upgrade. I compared Linux x86-64 binaries; I don't see why the analysis doesn't apply to OS X's Mach-O files, but it's possible the results are different there. (The above crash is from OS X, and we have crashes using Rust 1.33 that do display std::panicking::rust_panic_with_hook and similar.) The ELF symbol table in both cases lists rust_panic_with_hook as _ZN3std9panicking20rust_panic_with_hook$UNIQUE_ID, so that wasn't the problem.

We then looked at the debug information. Rust 1.33 generated, according to readelf --debug-dump=info:

 <3><2155a724>: Abbrev Number: 301 (DW_TAG_subprogram) <2155a726> DW_AT_low_pc : 0x5738510 <2155a72a> DW_AT_high_pc : 0x6b2 <2155a72e> DW_AT_frame_base : 1 byte block: 54	(DW_OP_reg4 (esp)) <2155a730> DW_AT_linkage_name: (indirect string, offset: 0x9d7fc09): _ZN3std9panicking20rust_panic_with_hook17he447c38467745511E <2155a734> DW_AT_name : (indirect string, offset: 0x9d7fc45): rust_panic_with_hook <2155a738> DW_AT_decl_file : 11 <2155a739> DW_AT_decl_line : 447 <2155a73b> DW_AT_external : 1 <2155a73b> DW_AT_noreturn : 1 

Notice the existence of both DW_AT_name and DW_AT_linkage_name. Rust 1.34, in contrast, generated:

 <1><216d7afa>: Abbrev Number: 293 (DW_TAG_subprogram) <216d7afc> DW_AT_low_pc : 0x5734990 <216d7b00> DW_AT_high_pc : 0x6ae <216d7b04> DW_AT_name : (indirect string, offset: 0x9db1282): rust_panic_with_hook 

which drops the DW_AT_linkage_name and is also significantly less informative than its predecessor.

I'm not familiar enough with rustc to know what might have caused this regression. One of my colleagues pointed out #58208, which changed how various bits of panic infrastructure are imported into libstd. It's not clear to me whether it's that specific change, or how the compiler internally describes crate:: symbols to LLVM, or something else entirely.

cc @glandium @michaelwoerister