[PATCH v2] x86/Kconfig: Fix allyesconfig

[PATCH v2] x86/Kconfig: Fix allyesconfig

[Guenter Roeck]

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.

Fixes: 6f110a5e4f99 ("Disable SLUB_TINY for build testing")
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: Disable KASAN unconditionally for test builds

 lib/Kconfig.kasan | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f82889a830fa..190297f2ff83 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -37,7 +37,7 @@ menuconfig KASAN
 		     (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
 		    CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
 		   HAVE_ARCH_KASAN_HW_TAGS
-	depends on SYSFS && !SLUB_TINY
+	depends on SYSFS && !SLUB_TINY && !COMPILE_TEST
 	select STACKDEPOT_ALWAYS_INIT
 	help
 	  Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
-- 
2.45.2

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

[Andrew Morton]

On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@roeck-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?

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

[Guenter Roeck]

On 4/16/25 17:03, Andrew Morton wrote:
> On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@roeck-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.

Guenter

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

[Andrew Morton]

On Wed, 16 Apr 2025 17:17:00 -0700 Guenter Roeck <linux@roeck-us.net> wrote:

> On 4/16/25 17:03, Andrew Morton wrote:
> > On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@roeck-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
 
 /* 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.

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

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

[Guenter Roeck]

On 4/16/25 17:03, Andrew Morton wrote:
> On Wed, 16 Apr 2025 16:05:59 -0700 Guenter Roeck <linux@roeck-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?

As mentioned before, increasing KERNEL_IMAGE_SIZE did not help.
However, it turns out that this works:

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ccdc45e5b759..647d4f47486d 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -468,8 +468,10 @@ SECTIONS
  /*
   * The ASSERT() sink to . is intentional, for binutils 2.14 compatibility:
   */
+#ifndef CONFIG_COMPILE_TEST
  . = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
            "kernel image bigger than KERNEL_IMAGE_SIZE");
+#endif

I'll send v3.

Guenter