[llvm-bugs] [Bug 38990] New: llvm-dwarfdump doesn't apply Split DWARF cu_index for debug_loc.dwo

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38990

            Bug ID: 38990
           Summary: llvm-dwarfdump doesn't apply Split DWARF cu_index for
                    debug_loc.dwo
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: Wolfgang_Pieb at playstation.sony.com
          Reporter: dblaikie at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20888
  --> https://bugs.llvm.org/attachment.cgi?id=20888&action=edit
Incomplete patch

Dumping large dwps produces a bunch of parse failures on debug_loc because the
cu_index entry for debug_loc is not accounted for when parsing the debug_loc
section.

While this example doesn't produce the error message, it does show the bug:

a.cpp:
  void y();
  void a(int i) {
    y();
    asm("" : : : "rdi");
  }

b.cpp:
  void b(int i) { asm("" : : : "rdi"); }

$ clang++-tot -gsplit-dwarf a.cpp b.cpp -c -O1 && llvm-dwp a.dwo b.dwo -o
ab.dwp && llvm-dwarfdump-tot ab.dwp | grep RDI
  Addr idx 0 (w/ length 6): DW_OP_reg5 RDI)
  Addr idx 0 (w/ length 6): DW_OP_reg5 RDI)

But run each .dwo file individually through dwarfdump:

$ llvm-dwarfdump-tot a.dwo b.dwo | grep RDI
  Addr idx 0 (w/ length 6): DW_OP_reg5 RDI)
  Addr idx 0 (w/ length 0): DW_OP_reg5 RDI)


Note the difference in length of these location list entries. This shows that
when dumping b.cpp's CU in ab.dwp, it's reading a.cpp's location list instead
of b.cpp's.

I've attached half a patch that was meant to start plumbing this through. It
isn't quite tied into the actual index lookup/offset yet - in part because of
some issues with the design there, that I'll file in a separate couple of bugs.

There's some other cleanup in this patch too - welcome to commit those parts,
or undo them, etc.

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