Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Sep 22, 2026 at 11:20:00AM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:
> Verify that the __bug_table entry emitted by ARCH_WARN_ASM has a correct
> bug_addr displacement — i.e. the arch's trap label reference resolves to
> the trap instruction — by calling find_bug() with the exact virtual address
> of the trap, mirroring what the real trap handler does.
> 
> To support all architectures, each arch that implements ARCH_WARN_ASM now
> defines ARCH_WARN_ASM_TRAP_LABEL, a string constant naming the local label
> at which the trap instruction is placed:
> 
>   x86       "1"     (ud2 at label 1:)
>   powerpc   "1"     (twi at label 1:)
>   riscv     "1"     (ebreak at label 1:)
>   arm64     "14471" (brk placed at 14471: by __BUG_ENTRY_END)
>   s390      "0"     (mc at label 0:)
> 
> The label is used consistently: in ARCH_WARN_ASM itself, in the
> bug_addr back-reference inside __BUG_ENTRY / _EMIT_BUG_ENTRY, 


> diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
> index 23ab05438269..6cca8880660e 100644
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -62,8 +62,9 @@ extern void __WARN_trap(struct bug_entry *bug, ...);
>  #define HAVE_ARCH_BUG_FORMAT_ARGS
>  #endif
>  
> +#define ARCH_WARN_ASM_TRAP_LABEL "1"
>  #define __BUG_ENTRY(format, file, line, flags)				\
> -	"\t.long 1b - ."	"\t# bug_entry::bug_addr\n"		\
> +	"\t.long " ARCH_WARN_ASM_TRAP_LABEL "b - ." "\t# bug_entry::bug_addr\n" \
>  	__BUG_ENTRY_FORMAT(format)					\
>  	__BUG_ENTRY_VERBOSE(file, line)					\
>  	"\t.word " flags	"\t# bug_entry::flags\n"
> @@ -101,7 +102,7 @@ do {									\
>  	"99:\n"								\
>  	"\t.string \"\"\n"						\
>  	".popsection\n"							\
> -	"1:\t " ASM_UD2 "\n"						\
> +	ARCH_WARN_ASM_TRAP_LABEL ":\t " ASM_UD2 "\n"			\
>  	_BUG_FLAGS_ASM("99b", file, line, flags, size, "")
>  
>  #else

Not really a fan of that. And I can't really tell what you're doing with
it either. The kunit is in Rust and thus unreadable :-(

I would rather you fix up is_valid_bugaddr(), some architectures seem to
have an always true stub because of the callchains always being from the
break instruction.