linux-kernel - Re: [PATCH v2 10/12] x86_64/bug: Implement __WARN

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Message-ID: <pwodqwmh6k64vg2hz2wniqwfwgcqiptq63u7xbpca7afianiep@5rcivow4kxlb>
Date: Mon, 17 Nov 2025 09:22:42 +0000
From: Maciej Wieczór-Retman <m.wieczorretman@...me>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kees@...nel.org, acarmina@...hat.com, jpoimboe@...nel.org, mark.rutland@....com, torvalds@...uxfoundation.org, maciej.wieczor-retman@...el.com
Subject: Re: [PATCH v2 10/12] x86_64/bug: Implement __WARN_printf()

On 2025-11-11 at 10:54:42 +0100, Peter Zijlstra wrote:
>On Mon, Nov 10, 2025 at 12:46:43PM +0100, Peter Zijlstra wrote:
>
>>  #endif /* _ASM_X86_BUG_H */
>> --- a/arch/x86/kernel/traps.c
>> +++ b/arch/x86/kernel/traps.c
>> @@ -102,25 +102,37 @@ __always_inline int is_valid_bugaddr(uns
>>   * UBSan{0}:     67 0f b9 00             ud1    (%eax),%eax
>>   * UBSan{10}:    67 0f b9 40 10          ud1    0x10(%eax),%eax
>>   * static_call:  0f b9 cc                ud1    %esp,%ecx
>> + * __WARN_trap:  67 48 0f b9 39          ud1    (%ecx),%reg
>>   *
>> - * Notably UBSAN uses EAX, static_call uses ECX.
>> + * Notable, since __WARN_trap can use all registers, the distinction between
>> + * UD1 users is through R/M.
>>   */
>
>Maciej; you were working on making KASAN emit UD1 instructions, right?
>Where are you with those patches and are we conflicting on the encoding?

I noticed your comment on my KASAN series so I'll just reply there.

>
>/me goes find the emails.. Yeah, I suggested UD1 /1, specifically:
>
>	ud1 xx(%ecx), %ecx
>
>and that does conflict. How about I switch to using:
>
>	ud1 (%edx), %reg
>
>for this?

Thanks for asking, that sounds good :)