[PATCH] D60487: [llvm] Prevent duplicate files in debug line header in dwarf 5: another attempt

[Ali Tamur via Phabricator via llvm-commits]

tamur created this revision.
tamur added reviewers: dblaikie, probinson, aprantl, echristo, espindola.
Herald added subscribers: llvm-commits, rupprecht, MaskRay, hiraditya, arichardson, javed.absar, emaste.
Herald added a project: LLVM.

Another attempt to land the changes in debug line header to prevent duplicate files in Dwarf 5. I rolled back my previous commit because of a mistake in generating the object file in a test. Meanwhile, I addressed some offline comments and changed the implementation; the largest difference is that MCDwarfLineTableHeader does not keep DwarfVersion but gets it as a parameter. I also merged the patch to fix two lld tests that will strt to fail into this patch.

      

Original Commit:  https://reviews.llvm.org/D59515

      

Original Message:
Motivation: In previous dwarf versions, file name indexes started from 1, and the primary source file was not explicit. Dwarf 5 standard (6.2.4) prescribes the primary source file to be explicitly given an entry with an index number 0.

      

The current implementation honors the specification by just duplicating the main source file, once with index number 0, and later maybe with another index number. While this is compliant with the letter of the standard, the duplication causes problems for consumers of this information such as lldb. (Some files are duplicated, where only some of them have a line table although all refer to the same file)

      

With this change, dwarf 5 debug line section files always start from 0, and the zeroth entry is not duplicated whenever possible. This requires different handling of dwarf 4 and dwarf 5 during generation (e.g. when a function returns an index zero for a file name, it signals an error in dwarf 4, but not in dwarf 5) However, I think the minor complication is worth it, because it enables all consumers (lldb, gdb, dwarfdump, objdump, and so on) to treat all files in the file name list homogenously.


Repository:
  rL LLVM

https://reviews.llvm.org/D60487

Files:
  lld/test/ELF/debug-line-obj.s
  lld/test/ELF/debug-line-str.s
  llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
  llvm/include/llvm/MC/MCDwarf.h
  llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
  llvm/lib/MC/MCAsmStreamer.cpp
  llvm/lib/MC/MCContext.cpp
  llvm/lib/MC/MCDwarf.cpp
  llvm/test/MC/ARM/dwarf-asm-multiple-sections.s
  llvm/test/MC/ELF/debug-mixed-md5.ll
  llvm/test/MC/ELF/dwarf-file0.s
  llvm/test/tools/llvm-objdump/Inputs/embedded-source
  llvm/test/tools/llvm-objdump/X86/function-sections-line-numbers.s

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