[PATCH] Check for working assembler --gdwarf-[45] options

[H.J. Lu]

On Fri, Oct 16, 2020 at 11:17 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Fri, Oct 16, 2020 at 10:58:34AM -0700, H.J. Lu wrote:
> > Don't set HAVE_AS_GDWARF_5_DEBUG_FLAG nor HAVE_AS_WORKING_DWARF_4_FLAG
> > if there is an extra assembly input file in debug info generated by
> > --gdwarf-5/--gdwarf-4:
> >
> > https://sourceware.org/bugzilla/show_bug.cgi?id=25878
> > https://sourceware.org/bugzilla/show_bug.cgi?id=26740
> >
> > Also replace success with dwarf4_success in the 32-bit --gdwarf-4 check.
> >
> > OK for master?
> >
> >       PR bootstrap/97451
> >       * configure.ac (HAVE_AS_GDWARF_5_DEBUG_FLAG): Don't define if
> >       there is an extra assembly input file in debug info.
> >       (HAVE_AS_WORKING_DWARF_4_FLAG): Likewise.  Replace success with
> >       dwarf4_success in the 32-bit --gdwarf-4 check.
> >       * configure: Regenerated.
>
> The HAVE_AS_GDWARF_5_DEBUG_FLAG macro should be solely about whether
> -gdwarf-5 can be passed to as, nothing else.  That is because it is not only
> used to decide if we can pass -gdwarf-5 to as for assembly of e.g. *.c
> compilation, but also if we can pass it to as when gcc driver is invoked on
> *.s and *.S.  And in that case the problems with -gdwarf-N having unwanted
> effects on assembly with compiler generated .debug_info etc. sections.
> don't really matter.
>
> The HAVE_AS_WORKING_DWARF_4_FLAG perhaps could be renamed to
> ...DWARF_N_FLAG, it is meant to check for whether we can safely pass the
> option also for *.c etc. compilation when we emit debug info sections by the
> compiler.
>
> For that, the question is, are all the issues already fixed on the binutils
> trunk?  As in, do I get identical object files e.g. for -gdwarf-2

Not yet.  This patch:

https://sourceware.org/pipermail/binutils/2020-October/113744.html

is needed for binutils master branch.  BTW, binutils 2.35 and 2.35.1 are
broken.

> compilation no matter whether the compiler passes -gdwarf-2 to gas or not
> (assuming dwarf 2 is the default in gas) when compiling various *.c/*.C
> files?  Ditto for modified gas that would default to other .debug_line
> versions and corresponding gcc -gdwarf-N flag and passing vs. not passing
> that -gdwarf-N to gas?
>
> The hope is that -gdwarf-N to gas would have two functions:
> 1) if the assembly doesn't contain .debug* sections/.file/.loc directives,
>    emit debug info (mainly .debug_line) for the assembler file in order to
>    be able to debug those
> 2) if the assembly does contain .debug* sections/.file/.loc directives,
>    only change the version of the .debug_line generated for the .file/.loc
>    directives, but nothing else; keep all .debug* sections but .debug_line
>    as is


-- 
H.J.