[llvm-bugs] [Bug 30750] New: symbolizer.o should be buildable with a regular cmake rule

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30750

            Bug ID: 30750
           Summary: symbolizer.o should be buildable with a regular cmake
                    rule
           Product: compiler-rt
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: compiler-rt
          Assignee: unassignedbugs at nondot.org
          Reporter: peter at pcc.me.uk
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 17471
  --> https://llvm.org/bugs/attachment.cgi?id=17471&action=edit
attempt

The internal symbolizer.o object is currently built with the script
compiler-rt/lib/sanitizer_common/symbolizer/scripts/build_symbolizer.sh.

We should really be using a simpler approach to building this object
file, and it should be available as a regular cmake rule. Conceptually, we
want to be doing "ld -r" followed by "objcopy -G" to create a relocatable
object file with only our entry points exposed. Attached is an attempt at doing
this in cmake. However, this does not work at present due to linker and objcopy
bugs:
- the presence of local symbols named the same as global symbols confuses at
  least bfd and gold, so we need to rename local symbols
- ld.gold fails to link symbolizer0.o (fails an assertion)
- ld.bfd succeeds, but seemingly creates an invalid .eh_frame section
(segfaults
  in the unwinder)
- ld.lld succeeds but creates multiple .eh_frame sections which confuses
  objcopy into creating an invalid output file (lld refuses to accept it, gold
  creates an invalid .eh_frame, bfd fails assertions)
To the extent that these are bugs in lld and objcopy, we can probably fix the
bugs in lld and write our own llvm-objcopy (perhaps with a nicer interface for
doing this transformation), then call the tools directly from cmake.

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