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rustc_codegen_llvm: Give each codegen unit a unique DWARF name on all

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platforms, not just Apple ones.

To avoid breaking split DWARF, we need to ensure that each codegen unit has a
unique `DW_AT_name`. This is because there's a remote chance that different
codegen units for the same module will have entirely identical DWARF entries
for the purpose of the DWO ID, which would violate Appendix F ("Split Dwarf
Object Files") of the DWARF 5 specification. LLVM uses the algorithm specified
in section 7.32 "Type Signature Computation" to compute the DWO ID, which does
not include any fields that would distinguish compilation units. So we must
embed the codegen unit name into the `DW_AT_name`.

Closes #88521.
This commit is contained in:
Patrick Walton 2021-12-16 20:39:41 -08:00
parent c5ecc15704
commit c41fd760db
1 changed files with 19 additions and 8 deletions
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27
compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
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@ -1036,14 +1036,25 @@ pub fn compile_unit_metadata(
None => PathBuf::from(&*tcx.crate_name(LOCAL_CRATE).as_str()), None => PathBuf::from(&*tcx.crate_name(LOCAL_CRATE).as_str()),
}; };
// The OSX linker has an idiosyncrasy where it will ignore some debuginfo // To avoid breaking split DWARF, we need to ensure that each codegen unit
// if multiple object files with the same `DW_AT_name` are linked together. // has a unique `DW_AT_name`. This is because there's a remote chance that
// As a workaround we generate unique names for each object file. Those do // different codegen units for the same module will have entirely
// not correspond to an actual source file but that is harmless. // identical DWARF entries for the purpose of the DWO ID, which would
if tcx.sess.target.is_like_osx { // violate Appendix F ("Split Dwarf Object Files") of the DWARF 5
name_in_debuginfo.push("@"); // specification. LLVM uses the algorithm specified in section 7.32 "Type
name_in_debuginfo.push(codegen_unit_name); // Signature Computation" to compute the DWO ID, which does not include
} // any fields that would distinguish compilation units. So we must embed
// the codegen unit name into the `DW_AT_name`. (Issue #88521.)
//
// Additionally, 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 for these two issues, we generate unique names for each
// object file. Those do not correspond to an actual source file but that
// is harmless.
name_in_debuginfo.push("@");
name_in_debuginfo.push(codegen_unit_name);
debug!("compile_unit_metadata: {:?}", name_in_debuginfo); debug!("compile_unit_metadata: {:?}", name_in_debuginfo);
let rustc_producer = let rustc_producer =