[Bug gas/28149] debug info with wrong file association

[i at maskray dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=28149

Fangrui Song <i at maskray dot me> changed:

           What    |Removed                     |Added
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                 CC|                            |i at maskray dot me

--- Comment #5 from Fangrui Song <i at maskray dot me> ---
(In reply to Alan Modra from comment #4)
> I can reproduce the comment #3 behaviour only when using -Wa,-gdwarf or
> similar gas options when using gcc-10.  gcc-11 and gcc-12 pass -gdwarf-5 to
> gas.  That seems to be the source of these problems, which is that -gdwarf*
> passed to gas means not only to select the DWARF level but also have gas
> generate its own DWARF line info.
> 
> So why is gcc passing -gdwarf-5 to gas?  That seems quite silly!  Can't gas
> figure the dwarf level out itself?  Note that current gas decides on dwarf5
> if seeing a .file or .loc specifying file 0.

https://gcc.gnu.org/pipermail/gcc-patches/2020-September/553527.html had the
discussion for the -gdwarf-5 behavior.

gas' detection of DWARF v5 .debug_line was added later:
https://sourceware.org/pipermail/binutils/2021-January/115000.html

If DWARF v6 or a future version ever bumps the line table version again (after
v2->v5), perhaps having a directive is fine. LLVM folks do not object to a
directive (https://reviews.llvm.org/D94882). I agree that passing -gdwarf-* to
gas is probably not very useful.

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