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

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Message-ID: <20201104000016.GA2399651@rani.riverdale.lan>
Date:   Tue, 3 Nov 2020 19:00:16 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH] Kbuild: implement support for DWARF5

On Wed, Oct 21, 2020 at 06:21:06PM -0700, Nick Desaulniers wrote:
> DWARF5 is the latest standard of the DWARF debug info format.
> 
> Feature detection of DWARF5 is onerous, especially given that we've
> removed $(AS), so we must query $(CC) for DWARF5 assembler directive
> support. Further -gdwarf-X where X is an unsupported value doesn't
> produce an error in $(CC). GNU `as` only recently gained support for
> specifying -gdwarf-5.

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?