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

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Date:   Tue, 1 Nov 2022 14:57:07 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
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, sedat.dilek@...il.com
Subject: Re: [PATCH] Makefile.debug: support for -gz=zstd

On Tue, Nov 1, 2022 at 3:49 AM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On Mon, Oct 24, 2022 at 10:44 AM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > 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?"
>
> Hi Masahiro,
> What are your thoughts on the above?


We renamed CONFIG options from time to time.
We should strive to update in-tree defconfigs,
but we did not care about external users very much.
(we rely on "make oldconfig" showing new options
and asking users for their choice.)

So, I like Sedat's DEBUG_INFO_COMPRESSED_{ZLIB,ZSTD,NONE}.
(and it is consist with CONFIG_INITRAMFS_COMPRESSION_*)

-- 
Best Regards
Masahiro Yamada