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

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 19.08.2026 2:18 PM, Mukesh Kumar Chaurasiya (IBM) wrote:
> 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.
>
> 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.
>
> 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.
>
> Suggested-by: FUJITA Tomonori <tomo@flapping.org>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>

Tested on PowerPC LPAR + 7.3.0-rc3 by creating a small .rs module to

trigger ARCH_WARN_ASM.

Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

> ---
>   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

-- 
Thanks and Regards
R.Nageswara Sastry