Re: [PATCH v2 10/12] x86_64/bug: Implement __WARN_printf()

[Peter Zijlstra <peterz@infradead.org>]

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?

/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?