Message-ID: <b35dc3bb-71ca-4f5e-af29-8e1605ec5bde@roeck-us.net>
Date: Wed, 16 Apr 2025 20:10:19 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Alexander Potapenko <glider@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>, kasan-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] x86/Kconfig: Fix allyesconfig

On 4/16/25 18:28, Andrew Morton wrote:
> On Wed, 16 Apr 2025 17:17:00 -0700 Guenter Roeck <linux@...ck-us.net> wrote:
> 
>> On 4/16/25 17:03, Andrew Morton wrote:
>>> On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@...ck-us.net> 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

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