[Bug gas/26740] Extra filename generated by --gdwarf-4

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26740

--- Comment #3 from Mark Wielaard <mark at klomp dot org> ---
(In reply to H.J. Lu from comment #2)
> (In reply to Mark Wielaard from comment #1)
> > The issue is that some instructions are emitted (dwarf2_emit_insn is called)
> > before the first .file <NUMBER> directive has been seen. This allocates x.s
> > (the input file) as first file entry. Later when the actual .file 1
> > lbasename.c and .file 2 safe-ctype are seen the x.s entry is moved to entry
> > 3. We don't record that we never actually use that entry and so we still
> > emit it.
> 
> Is this a GCC bug? Even if it is, assembler shouldn't generate bad debug
> info.

I don't think so. Although it might help if gcc emitted the .file 1 directive
earlier. The debug info isn't really bad, but it does contain an unused file
name which it really shouldn't. I am not yet sure how to fix that. 

In gas/dwarf2dbg.c you see that the file entry is moved when a .file NUM is
seen and the file entry is auto_assigned. I wonder if we should just replace it
instead of moving if dwarf2_any_loc_directive_seen is false (because then we
know it has never been used).

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