linux-kernel - Re: [PATCH] Kbuild: implement support for DWARF5

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Message-ID: <20201104001703.GA2407187@rani.riverdale.lan>
Date:   Tue, 3 Nov 2020 19:17:03 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH] Kbuild: implement support for DWARF5

On Tue, Nov 03, 2020 at 04:05:36PM -0800, Nick Desaulniers wrote:
> On Tue, Nov 3, 2020 at 4:00 PM Arvind Sankar <nivedita@...m.mit.edu> wrote:
> >
> > On Wed, Oct 21, 2020 at 06:21:06PM -0700, Nick Desaulniers wrote:
> > > Further -gdwarf-X where X is an unsupported value doesn't
> > > produce an error in $(CC).
> >
> > Do you have more details here? On godbolt.org, gcc does report an error
> > for unsupported dwarf versions.
> >
> > https://godbolt.org/z/G35798
> >
> > gcc does not seem to pass the -gdwarf-* options to the assembler when
> > compiling C source. For assembler, gcc will pass an appropriate option
> > depending on the version of binutils it was configured with: if the
> > assembler doesn't support dwarf-5 it can call it with --gdwarf2 for eg.
> >
> > If the user is using a properly configured toolchain it doesn't look
> > like it should be an issue to just use cc-option?
> 
> I wrote the base patch back in May, and didn't revisit until recently.
> I could have sworn the cc-option silently failed for the check
> cc-option does, which is /dev/null input.  I need to recheck that, but
> it doesn't hurt to simply include it for now, which I've done in a v2
> I'm about to send.
> -- 
> Thanks,
> ~Nick Desaulniers

This is giving me deja vu about the -gz=zlib option.

Didn't Masahiro fix the cc-option issue with
  4d0831e8a029 ("kconfig: unify cc-option and as-option")

The existing -Wa,-gdwarf-2 in the Makefile seems bogus, btw. GCC 4.9.0
at least appears to pass on --gdwarf2 automatically.