[PATCH 16/15] bugs/s390: Use in 'cond_str' to __EMIT_BUG()

[Ingo Molnar]

* Heiko Carstens <hca@xxxxxxxxxxxxx> wrote:

> On Thu, May 15, 2025 at 02:46:39PM +0200, Ingo Molnar wrote:
> > Pass in the condition string from __WARN_FLAGS(), but do not
> > concatenate it with __FILE__, because the __bug_table is
> > apparently indexed by 16 bits and increasing string size
> > overflows it on defconfig builds.
> 
> Could you provide your change which didn't work?
> 
> I cannot see how anything would overflow. Trying the below on top of
> your series seems to work like expected.
> 
> In order to keep things easy this drops the mergeable section trick
> and results in a small increase of the rodata section, but I doubt
> that would explain what you have seen.
> 
> Also allyesconfig builds without errors.
> 
> diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
> index 30f8785a01f5..837bfbde0c51 100644
> --- a/arch/s390/include/asm/bug.h
> +++ b/arch/s390/include/asm/bug.h
> @@ -11,16 +11,14 @@
>  #define __EMIT_BUG(cond_str, x) do {				\
>  	asm_inline volatile(					\
>  		"0:	mc	0,0\n"				\
> -		".section .rodata.str,\"aMS\",@progbits,1\n"	\
> -		"1:	.asciz	\""__FILE__"\"\n"		\
> -		".previous\n"					\
>  		".section __bug_table,\"aw\"\n"			\
> -		"2:	.long	0b-.\n"				\
> -		"	.long	1b-.\n"				\
> -		"	.short	%0,%1\n"			\
> -		"	.org	2b+%2\n"			\
> +		"1:	.long	0b-.\n"				\
> +		"	.long	%0-.\n"				\
> +		"	.short	%1,%2\n"			\
> +		"	.org	1b+%3\n"			\
>  		".previous\n"					\
> -		: : "i" (__LINE__),				\
> +		: : "i" (WARN_CONDITION_STR(cond_str) __FILE__),\
> +		    "i" (__LINE__),				\
>  		    "i" (x),					\
>  		    "i" (sizeof(struct bug_entry)));		\
>  } while (0)

So I'm not sure what happened: I tried to reproduce what I did 
originally, but my naive patch ran into assembler build errors when a 
WARN_ON() macro tried to use the '%' C operator, such as 
fs/crypto/crypto.c:123:

 include/linux/compiler_types.h:497:20: error: invalid 'asm': invalid %-code
 arch/s390/include/asm/bug.h:12:2: note: in expansion of macro 'asm_inline'
 arch/s390/include/asm/bug.h:50:2: note: in expansion of macro '__EMIT_BUG'
 include/asm-generic/bug.h:119:3: note: in expansion of macro '__WARN_FLAGS'
 fs/crypto/crypto.c:123:6: note: in expansion of macro 'WARN_ON_ONCE'

Which corresponds to:

        if (WARN_ON_ONCE(len % FSCRYPT_CONTENTS_ALIGNMENT != 0))
                return -EINVAL;

I'm quite sure I never saw these build errors - I saw linker errors 
related to the u16 overflow I documented in the changelog. (Note to 
self: copy & paste more of the build error context next time around.)

Your version doesn't have that build problem, so I picked it up with 
the changelog below and your Signed-off-by. Does that look good to you?

Thanks,

	Ingo

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