linux-kernel - Re: [PATCH] Makefile.debug: support for -gz=zstd

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Date:   Mon, 24 Oct 2022 10:44:13 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     sedat.dilek@...il.com, Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Sedat Dilek <sedat.dilek@....com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Terrell <terrelln@...com>, Tom Rix <trix@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        David Gow <davidgow@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Isabella Basso <isabbasso@...eup.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] Makefile.debug: support for -gz=zstd

On Sun, Oct 23, 2022 at 8:46 AM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> On Thu, Oct 20, 2022 at 8:43 PM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > On Thu, Oct 20, 2022 at 10:56:49AM -0700, Nick Desaulniers wrote:
> > > +config DEBUG_INFO_UNCOMPRESSED
> > > +     bool "Don't compress debug information"
> > > +     help
> > > +       Don't compress debug info sections.
> > > +
> > >  config DEBUG_INFO_COMPRESSED
>
> Also, I prefer...
>
> DEBUG_INFO_COMPRESSED_NONE
> DEBUG_INFO_COMPRESSED_ZLIB
> DEBUG_INFO_COMPRESSED_ZSTD
>
> Following...
>
> $ ld.lld-16 -v
> Debian LLD 16.0.0 (compatible with GNU linkers)
>
> $ ld.lld-16 --help | grep compress-debug-sections
>  --compress-debug-sections=[none,zlib,zstd]

It's a good suggestion, though I deliberately did not modify the
identifier used for the existing DEBUG_INFO_COMPRESSED.  No defconfigs
set DEBUG_INFO_COMPRESSED explicitly, but I think one issue with
changing the identifier of existing kconfigs is that upon upgrading to
newer kernel sources, if you run `make oldmodconfig` if you previously
had DEBUG_INFO_COMPRESSED=y, kconfig doesn't know that that option has
been renamed to DEBUG_INFO_COMPRESSED_ZLIB so it would be silently
disabled, and image sizes would increase due to uncompressed debug
info. That seems developer hostile.

Masahiro, what are your thoughts on how to proceed? Should I change
the pre-existing Kconfig identifier, or "let sleeping dogs lie?"
-- 
Thanks,
~Nick Desaulniers