Auto merge of #82102 - nagisa:nagisa/fix-dwo-name, r=davidtwco

Set path of the compile unit to the source directory

As part of the effort to implement split dwarf debug info, we ended up
setting the compile unit location to the output directory rather than
the source directory. Furthermore, it seems like we failed to remap the
prefixes for this as well!

The desired behaviour is to instead set the `DW_AT_GNU_dwo_name` to a
path relative to compiler's working directory. This still allows
debuggers to find the split dwarf files, while not changing the
behaviour of the code that is compiling with regular debug info, and not
changing the compiler's behaviour with regards to reproducibility.

Fixes #82074

cc `@alexcrichton` `@davidtwco`

1 files changed, 11 insertions, 8 deletions

diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index 6e7c0b3e347..d935fc83b72 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -979,7 +979,7 @@ pub fn compile_unit_metadata(
     // 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.
+    // not correspond to an actual source file but that is harmless.
     if tcx.sess.target.is_like_osx {
         name_in_debuginfo.push("@");
         name_in_debuginfo.push(codegen_unit_name);
@@ -992,17 +992,17 @@ pub fn compile_unit_metadata(
     let producer = format!("clang LLVM ({})", rustc_producer);
 
     let name_in_debuginfo = name_in_debuginfo.to_string_lossy();
+    let work_dir = tcx.sess.working_dir.0.to_string_lossy();
     let flags = "\0";
-
     let out_dir = &tcx.output_filenames(LOCAL_CRATE).out_directory;
     let split_name = if tcx.sess.target_can_use_split_dwarf() {
         tcx.output_filenames(LOCAL_CRATE)
-            .split_dwarf_filename(tcx.sess.split_debuginfo(), Some(codegen_unit_name))
+            .split_dwarf_path(tcx.sess.split_debuginfo(), Some(codegen_unit_name))
+            .map(|f| out_dir.join(f))
     } else {
         None
     }
     .unwrap_or_default();
-    let out_dir = out_dir.to_str().unwrap();
     let split_name = split_name.to_str().unwrap();
 
     // FIXME(#60020):
@@ -1024,12 +1024,12 @@ pub fn compile_unit_metadata(
     assert!(tcx.sess.opts.debuginfo != DebugInfo::None);
 
     unsafe {
-        let file_metadata = llvm::LLVMRustDIBuilderCreateFile(
+        let compile_unit_file = llvm::LLVMRustDIBuilderCreateFile(
             debug_context.builder,
             name_in_debuginfo.as_ptr().cast(),
             name_in_debuginfo.len(),
-            out_dir.as_ptr().cast(),
-            out_dir.len(),
+            work_dir.as_ptr().cast(),
+            work_dir.len(),
             llvm::ChecksumKind::None,
             ptr::null(),
             0,
@@ -1038,12 +1038,15 @@ pub fn compile_unit_metadata(
         let unit_metadata = llvm::LLVMRustDIBuilderCreateCompileUnit(
             debug_context.builder,
             DW_LANG_RUST,
-            file_metadata,
+            compile_unit_file,
             producer.as_ptr().cast(),
             producer.len(),
             tcx.sess.opts.optimize != config::OptLevel::No,
             flags.as_ptr().cast(),
             0,
+            // NB: this doesn't actually have any perceptible effect, it seems. LLVM will instead
+            // put the path supplied to `MCSplitDwarfFile` into the debug info of the final
+            // output(s).
             split_name.as_ptr().cast(),
             split_name.len(),
             kind,