linux-kernel - Re: linux-next: new objtool warnings

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Message-ID: <20251106114844.GT4067720@noisy.programming.kicks-ass.net>
Date: Thu, 6 Nov 2025 12:48:44 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Linux Next Mailing List <linux-next@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-kbuild@...r.kernel.org, Nicolas Schier <nsc@...nel.org>
Subject: Re: linux-next: new objtool warnings

On Wed, Nov 05, 2025 at 01:09:23PM -0700, Nathan Chancellor wrote:
> On Wed, Nov 05, 2025 at 08:16:13PM +0100, Peter Zijlstra wrote:
> > # make O=tmp-build clean
> > # make O=tmp-build allmodconfig
> > # make O=tmp-build -j64 vmlinux 2>&1 | grep "\[M\]"
> >   CC [M]  sound/sound_core.o
> >   CC [M]  virt/lib/irqbypass.o
> >   AS [M]  arch/x86/crypto/twofish-x86_64-asm_64.o
> >   CC [M]  arch/x86/crypto/twofish_glue.o
> >   CC [M]  samples/vfio-mdev/mtty.o
> >   CC [M]  sound/ac97_bus.o
> >   AS [M]  arch/x86/crypto/twofish-x86_64-asm_64-3way.o
> >   CC [M]  arch/x86/crypto/twofish_glue_3way.o
> 
> Thanks, I bisected this to commit d2d5cba5d92c ("kbuild: remove EXPERT
> and !COMPILE_TEST guarding from TRIM_UNUSED_KSYMS"), which explains
> everything when looking at Makefile:
> 
>   ifdef CONFIG_TRIM_UNUSED_KSYMS
>   # For the kernel to actually contain only the needed exported symbols,
>   # we have to build modules as well to determine what those symbols are.
>   KBUILD_MODULES := y
>   endif
> 
> Maybe we want to restore the !COMPILE_TEST dependency?

Urgh, yeah, I suppose we do want. This TRIM_UNUSED_KSYMS is cute if you
swing that way for a full build, but getting all modules built if you
just want a vmlinux is really somewhat unexpected.