[PATCH V2] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Christophe Leroy (CS GROUP)]

Le 10/09/2026 à 09:12, Mukesh Kumar Chaurasiya (IBM) a écrit :
> The Rust kernel infrastructure generates inline asm for WARN() via
> ARCH_WARN_ASM(file, line, flags, size), expanding it through a C
> preprocessor pass (generated_arch_warn_asm.rs.S) to produce an
> arch-specific asm template string for use in Rust's core::arch macros.
> 
> powerpc currently lacks ARCH_WARN_ASM and ARCH_WARN_REACHABLE, causing
> Rust builds to fail on powerpc with
> ```
> error: no rules expected `ARCH_WARN_ASM`
>     --> /home/linkmauve/dev/linux/wii/rust/kernel/generated_arch_warn_asm.rs:1:28
>      |
>    1 | ::kernel::concat_literals!(ARCH_WARN_ASM("{file}", "{line}", "{flags}", "{size}"))
>      |                            ^^^^^^^^^^^^^ no rules expected this token in macro call
>      |
>     ::: ../rust/kernel/lib.rs:279:1
>      |
> 279 | macro_rules! concat_literals {
>      | ---------------------------- when calling this macro
>      |
>      = note: while trying to match sequence start
> 
> error: no rules expected `ARCH_WARN_REACHABLE`
>     --> /home/linkmauve/dev/linux/wii/rust/kernel/generated_arch_reachable_asm.rs:1:28
>      |
>    1 | ::kernel::concat_literals!(ARCH_WARN_REACHABLE)
>      |                            ^^^^^^^^^^^^^^^^^^^ no rules expected this token in macro call
>      |
>     ::: ../rust/kernel/lib.rs:279:1
>      |
> 279 | macro_rules! concat_literals {
>      | ---------------------------- when calling this macro
>      |
>      = note: while trying to match sequence start
> 
> error: aborting due to 2 previous errors
> ```
> 
> Refactor _EMIT_BUG_ENTRY to accept explicit (file, line, flags) string
> arguments rather than relying on positional asm operand references
> (%0, %1, %2, %3). This allows the macro to be composed as a plain
> string concatenation, which is required for ARCH_WARN_ASM where no asm
> operand context exists.

For a cleaner _EMIT_BUG_ENTRY() macro, shouldn't it also pass the label 
where the trap sits as a macro argument instead of blindly relying on it 
being 1: ?

Christophe

> 
> Move the .org and .previous directives out of _EMIT_BUG_ENTRY and into
> the BUG_ENTRY() call site to preserve existing behaviour while enabling
> ARCH_WARN_ASM to supply its own size operand independently.
> 
> Add ARCH_WARN_REACHABLE as an empty define, matching the arm64
> convention, indicating that no additional reachability annotation is
> needed after a WARN on powerpc.
> 
> This brings powerpc into line with x86, arm64, s390, and riscv, all of
> which already define ARCH_WARN_ASM and ARCH_WARN_REACHABLE.
> 
> Reported-by: FUJITA Tomonori <tomo at flapping.org>
> Closes: https://lore.kernel.org/all/anG67Q6Y59kDqh-c@desktop
> Fixes: 73b741adb264 ("rust: Add PowerPC support")
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at gmail.com>
> ---
> Changelog:
> V1 -> V2:
> - commit message now has error, fixes tag and closes tag
> 
>   arch/powerpc/include/asm/bug.h | 28 ++++++++++++++++------------
>   1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 0db48977c70c..8aba39e0cf26 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -32,34 +32,38 @@
>   #endif /* verbose */
>   
>   #else /* !__ASSEMBLER__ */
> -/* _EMIT_BUG_ENTRY expects args %0,%1,%2,%3 to be FILE, LINE, flags and
> -   sizeof(struct bug_entry), respectively */
>   #ifdef CONFIG_DEBUG_BUGVERBOSE
> -#define _EMIT_BUG_ENTRY				\
> +#define _EMIT_BUG_ENTRY(file, line, flags)	\
>   	".section __bug_table,\"aw\"\n"		\
>   	"2:	.4byte 1b - .\n"		\
> -	"	.4byte %0 - .\n"		\
> -	"	.short %1, %2\n"		\
> -	".org 2b+%3\n"				\
> -	".previous\n"
> +	"	.4byte " file " - .\n"		\
> +	"	.short " line ", " flags "\n"
>   #else
> -#define _EMIT_BUG_ENTRY				\
> +#define _EMIT_BUG_ENTRY(file, line, flags)	\
>   	".section __bug_table,\"aw\"\n"		\
>   	"2:	.4byte 1b - .\n"		\
> -	"	.short %2\n"			\
> -	".org 2b+%3\n"				\
> -	".previous\n"
> +	"	.short " flags "\n"
>   #endif
>   
>   #define BUG_ENTRY(cond_str, insn, flags, ...)		\
>   	__asm__ __volatile__(				\
>   		"1:	" insn "\n"			\
> -		_EMIT_BUG_ENTRY				\
> +		_EMIT_BUG_ENTRY("%0", "%1", "%2")	\
> +		".org 2b+%3\n"				\
> +		".previous\n"				\
>   		: : "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i" (__LINE__),	\
>   		  "i" (flags),				\
>   		  "i" (sizeof(struct bug_entry)),	\
>   		  ##__VA_ARGS__)
>   
> +#define ARCH_WARN_ASM(file, line, flags, size)		\
> +		"1:	twi 31, 0, 0\n"			\
> +		_EMIT_BUG_ENTRY(file, line, flags)	\
> +		".org 2b+" size "\n"			\
> +		".previous\n"
> +
> +#define ARCH_WARN_REACHABLE
> +
>   /*
>    * BUG_ON() and WARN_ON() do their best to cooperate with compile-time
>    * optimisations. However depending on the complexity of the condition