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Improve build path mapping to produce clean relative paths in stack traces#102000
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Algunenano merged 2 commits intoApr 8, 2026
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Previously, `ENABLE_BUILD_PATH_MAPPING` used `-ffile-prefix-map=${SOURCE_DIR}=.`,
which mapped source paths to `./src/Foo.cpp` but left `DW_AT_comp_dir` pointing
at the build directory. The symbolizer joined them, producing paths like
`./ci/tmp/fast_build/./src/Foo.cpp` in out-of-tree CI builds.
Replace the single flag with two Clang-specific flags:
- `-fdebug-compilation-dir=.` — pins `DW_AT_comp_dir` to `.` unconditionally,
regardless of where the build directory is located.
- `-ffile-prefix-map=${SOURCE_DIR}/=` — strips the source root prefix including
the separator, leaving bare relative paths like `src/Foo.cpp`.
Also fix `Dwarf::LineNumberVM::getFullFileName` to skip a directory entry of `"."`
when building file paths. The DWARF 5 line number program stores the compilation
directory as an explicit entry (index 0), which after the prefix mapping becomes
`"."`. Prepending it produced `./src/Foo.cpp` for `.cpp` translation units while
inlined header frames (whose directory entries were absolute paths that mapped to
`src/Common`) showed as `src/Common/Foo.h` — inconsistent. Treating `"."` as
an empty directory makes all paths consistently bare relative.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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alexey-milovidov
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Apr 7, 2026
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LLVM Coverage ReportChanged lines: 100.00% (4/4) · Uncovered code |
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Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Stack traces now show clean bare relative paths (e.g.
src/Common/Exception.cpp) instead of paths polluted with the build directory (e.g../ci/tmp/fast_build/./src/Common/Exception.cpp).Description
ENABLE_BUILD_PATH_MAPPINGpreviously used-ffile-prefix-map=${SOURCE_DIR}=., which mapped source paths to./src/Foo.cppbut leftDW_AT_comp_dirpointing at the build directory. The symbolizer joined them, producing paths like./ci/tmp/fast_build/./src/Common/Exception.cppin out-of-tree CI builds.This PR replaces the single flag with two Clang-specific flags:
-fdebug-compilation-dir=.— pinsDW_AT_comp_dirto.unconditionally, regardless of where the build directory is located.-ffile-prefix-map=${SOURCE_DIR}/=— strips the source root prefix including the separator, leaving bare relative paths likesrc/Foo.cpp.It also fixes
Dwarf::LineNumberVM::getFullFileNameto skip a directory entry of"."when building file paths. The DWARF 5 line number program stores the compilation directory as an explicit entry (index 0), which after the prefix mapping becomes".". Prepending it produced./src/Foo.cppfor.cpptranslation units while inlined header frames showed assrc/Common/Foo.h— inconsistent. Treating"."as an empty directory makes all paths consistently bare relative.Before:
After:
Documentation entry for user-facing changes