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List:       binutils-bugs
Subject:    [Bug gas/25611] New: [DWARF-5] support for checksums in .file directives
From:       "ndesaulniers at google dot com" <sourceware-bugzilla () sourceware ! org>
Date:       2020-02-28 21:47:29
Message-ID: bug-25611-70 () http ! sourceware ! org/bugzilla/
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https://sourceware.org/bugzilla/show_bug.cgi?id=25611

            Bug ID: 25611
           Summary: [DWARF-5] support for checksums in .file directives
           Product: binutils
           Version: 2.35 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: ndesaulniers at google dot com
  Target Milestone: ---

I was playing around trying to enable -gdwarf-5 in the Linux kernel, and hit an
issue where it looks like clang is emitting .file directives like:

.file 1 "/home/nick/linux/init/do_mounts.c" md5
0x62e8a195aa9d4d8b466f84b7775ea4cd

with GAS producing errors like:
do_mounts.s:19: Error: junk at end of line, first unrecognized character is `m'

A quick grep through the DWARF-5 spec [0] doesn't mention anything about
assembly directives.  The docs on .file directives also doesn't mention this.
[1]

I assume this is maybe an extension that Clang implemented? IIUC, it's used by
debuggers to tell when/if a file has been modified.

Is this something that can be implemented in GNU as? I'm happy to also pursue a
command line flag in Clang to disable the emission of these checksums.

See also [2].

[0] http://www.dwarfstd.org/doc/DWARF5.pdf
[1] https://sourceware.org/binutils/docs/as/File.html#File
[2] https://bugs.llvm.org/show_bug.cgi?id=45040

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