Re: [PATCH] kbuild: Use --strip-unneeded with INSTALL_MOD_STRIP

From: Charlie Jenkins <charlie@rivosinc.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH] kbuild: Use --strip-unneeded with INSTALL_MOD_STRIP
Date: Thu, 30 Jan 2025 22:54:11 -0800	[thread overview]
Message-ID: <Z5xzkwwZAWRRLCdj@ghost> (raw)
In-Reply-To: <20250131035245.GA47826@ax162>

On Thu, Jan 30, 2025 at 08:52:45PM -0700, Nathan Chancellor wrote:
> On Wed, Jan 22, 2025 at 07:17:26PM -0800, Charlie Jenkins wrote:
> > On riscv, kernel modules end up with a significant number of local
> > symbols. This becomes apparent when compiling modules with debug symbols
> > enabled. Using amdgpu.ko as an example of a large module, on riscv the
> > size is 754MB (no stripping), 53MB (--strip-debug), and 21MB
> > (--strip-unneeded). ON x86, amdgpu.ko is 482MB (no stripping), 21MB
> > (--strip-debug), and 20MB (--strip-unneeded).
> > 
> > Use --strip-unneeded instead of --strip-debug to strip modules so
> > decrease the size of the resulting modules. This is particularly
> > relevant for riscv, but also marginally aids other architectures.
> > 
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> 
> Is there any sort of regression risk with this patch? If so, another
> option may be to give another level to INSTALL_MOD_STRIP like 2 so that
> INSTALL_MOD_STRIP=1 continues to behave as before but people can easily
> opt into this option. No strong opinion because I am not sure but was
> not sure if it was considered.

I do not believe this would cause regressions. The description on gnu
strip is:

"Remove all symbols that are not needed for relocation processing in
addition to debugging symbols and sections stripped by --strip-debug."

The description on llvm-strip is:

"Remove from the output all local or undefined symbols that are not
required by relocations. Also remove all debug sections."

gnu strip --strip-unneeded strips slightly more aggressively but it does
not appear this causes any issues.

> 
> Regardless:
> 
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Thanks!

- Charlie

>
> > ---
> >  scripts/Makefile.modinst | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
> > index f97c9926ed31b2b14601ff7773a2ea48b225628b..c22f35f6b9db3cac3923b9e787b219f752570642 100644
> > --- a/scripts/Makefile.modinst
> > +++ b/scripts/Makefile.modinst
> > @@ -80,7 +80,7 @@ quiet_cmd_install = INSTALL $@
> >  ifdef INSTALL_MOD_STRIP
> >  
> >  ifeq ($(INSTALL_MOD_STRIP),1)
> > -strip-option := --strip-debug
> > +strip-option := --strip-unneeded
> >  else
> >  strip-option := $(INSTALL_MOD_STRIP)
> >  endif
> > 
> > ---
> > base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04
> > change-id: 20250122-strip_unneeded-cab729310056
> > -- 
> > - Charlie
> > 