linux-kernel - Re: [PATCH] kbuild: Use --strip-unneeded with INSTALL_MOD

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <Z6JcgeDmt63MupyW@ghost>
Date: Tue, 4 Feb 2025 10:29:21 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] kbuild: Use --strip-unneeded with INSTALL_MOD_STRIP

On Tue, Feb 04, 2025 at 01:04:26PM +0900, Masahiro Yamada wrote:
> On Sat, Feb 1, 2025 at 6:33 AM Charlie Jenkins <charlie@...osinc.com> wrote:
> >
> > On Sat, Feb 01, 2025 at 12:10:02AM +0900, Masahiro Yamada wrote:
> > > On Fri, Jan 31, 2025 at 3:54 PM Charlie Jenkins <charlie@...osinc.com> wrote:
> > > >
> > > > 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@...osinc.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@...nel.org>
> > > >
> > > > Thanks!
> > > >
> > >
> > >
> > > It is true --strip-unneeded drops a lot of compiler-generated symbols, but
> > > it also drops real symbols that originate in the source code.
> > >
> > > So, this would give user-visible changes for kallsyms at least.
> >
> > Adding INSTALL_MOD_STRIP="--strip-unneeded" would be sufficient for
> > riscv. However, this has the downside that riscv will require different
> > flags than other architectures to get reasonably sized modules.
> 
> You can use INSTALL_MOD_STRIP=--strip-unneeded for all architecture if you like.
> 
> I assume this is a riscv issue. Specifically, riscv gcc.
> With LLVM=1, I see much smaller riscv modules using INSTALL_MOD_STRIP=1.
> 
> --strip-unneeded is needlessly aggressive for other architectures,
> and I do not see a good reason to change the default.

Yes it is primarily an issue with riscv GCC. I was hoping for something
more standardized so that other people using riscv GCC wouldn't
encounter this. Would it be reasonable to add this flag by default only
for the riscv architecture, or do you think it's just better to leave it
up to the user's choice?

- Charlie

> 
> 
> 
> 
> 
> 
> 
> 
> 
> >
> > I believe these symbols are only useful for debugging, is there a
> > usecase for them to be available when the user has modules compiled with
> > INSTALL_MOD_STRIP=1?
> >
> > - Charlie
> >
> > >
> > >
> > > $ riscv64-linux-gnu-nm  -n
> > > /tmp/strip-unneeded/lib/modules/6.13.0-09760-g69e858e0b8b2/kernel/drivers/gpu/drm/amd/amdgpu/amdgpu.ko
> > >  > /tmp/symbol-with-strip-unneeded
> > > $ riscv64-linux-gnu-nm  -n
> > > /tmp/strip-debug/lib/modules/6.13.0-09760-g69e858e0b8b2/kernel/drivers/gpu/drm/amd/amdgpu/amdgpu.ko
> > >  > /tmp/symbol-with-strip-debug
> > >
> > > $  diff -u /tmp/symbol-with-strip-debug  /tmp/symbol-with-strip-unneeded
> > >  [ snip ]
> > >  00000000001676cc t uvd_v6_0_ring_test_ring
> > >  0000000000167802 t uvd_v6_0_ring_emit_pipeline_sync
> > >  0000000000167a02 t uvd_v6_0_ring_emit_fence
> > > -0000000000167b58 r CSWTCH.2
> > > -0000000000167b68 r abm_settings
> > > -0000000000167b80 r abm_config
> > > -0000000000167b90 r min_reduction_table_v_2_2
> > > -0000000000167ba0 r max_reduction_table_v_2_2
> > > -0000000000167bb0 r min_reduction_table
> > > -0000000000167bc0 r max_reduction_table
> > > -0000000000167bd0 r custom_backlight_curve0
> > >  0000000000167c38 r abm_settings_config2
> > >  0000000000167c70 r abm_settings_config1
> > >  0000000000167ca8 r abm_settings_config0
> > >
> > >
> > >
> > >
> > > --
> > > Best Regards
> > > Masahiro Yamada
> 
> 
> 
> --
> Best Regards
> Masahiro Yamada