Re: [PATCH v2] x86/Kconfig: Fix allyesconfig

[Guenter Roeck]

On 4/16/25 18:28, Andrew Morton wrote:
> On Wed, 16 Apr 2025 17:17:00 -0700 Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > On 4/16/25 17:03, Andrew Morton wrote:
> > > On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > >
> > > > 64-bit allyesconfig builds fail with
> > > >
> > > > x86_64-linux-ld: kernel image bigger than KERNEL_IMAGE_SIZE
> > > >
> > > > Bisect points to commit 6f110a5e4f99 ("Disable SLUB_TINY for build
> > > > testing") as the responsible commit. Reverting that patch does indeed
> > > > fix the problem. Further analysis shows that disabling SLUB_TINY enables
> > > > KASAN, and that KASAN is responsible for the image size increase.
> > > >
> > > > Solve the build problem by disabling KASAN for test builds.
> > >
> > > Excluding KASAN from COMPILE_TEST builds is regrettable.
> > >
> > > Can we address this some other way?  One way might be to alter or
> > > disable the KERNEL_IMAGE_SIZE check if COMPILE_TEST?  That will be sad
> > > for anyone who tries to boot a COMPILE_TEST kernel, but who the heck
> > > does that?
> >
> > I tried increasing the limit. It didn't work. With the RFC I sent earlier
> > I made it dependent on allmodconfig, but Linus said I should just disable
> > it for test builds (which was the cases anyway until commit 6f110a5e4f99).
> >
> > Personally I don't have a preference either way. I can also do nothing and
> > stop testing allyesconfig. That would help reducing the load on my testbed,
> > so I would be all for it.
>
> How about this?
>
>
>
> --- a/arch/x86/kernel/vmlinux.lds.S~a
> +++ a/arch/x86/kernel/vmlinux.lds.S
> @@ -466,10 +466,19 @@ SECTIONS
>   }
>   
>   /*
> - * The ASSERT() sink to . is intentional, for binutils 2.14 compatibility:
> + * COMPILE_TEST kernels can be large - CONFIG_KASAN, for example, can cause
> + * this.  Let's assume that nobody will be running a COMPILE_TEST kernel and
> + * let's assert that fuller build coverage is more valuable than being able to
> + * run a COMPILE_TEST kernel.
> + */
> +#ifndef CONFIG_COMPILE_TEST
> +/*
> +/*
> + * The ASSERT() sync to . is intentional, for binutils 2.14 compatibility:
>    */
>   . = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
>   	   "kernel image bigger than KERNEL_IMAGE_SIZE");
> +#endif
>   

Yes, that is what I ended up doing with v3 (thanks for the idea), lacking the comment.
Guess I'll need to send v4, but I'll wait a bit to see if there is feedback from others.

>   /* needed for Clang - see arch/x86/entry/entry.S */
>   PROVIDE(__ref_stack_chk_guard = __stack_chk_guard);
> _
>
>
> (contains gratuitous s/sink/sync/)
>
>
> I'd like to add
>
> #else
> 	WARN((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
>   	   "kernel image bigger than KERNEL_IMAGE_SIZE - kernel probably will not work");
> #endif	/* CONFIG_COMPILE_TEST */
>
> but I lack the patience to figure out how to do that.

WARN is a define which declares C code. That doesn't work in linker scripts.
I only got #ifdef to work. I did not find a linker script command which would
be equivalent to WARN(). Maybe someone else knows if it is possible and how
to do it.

Guenter