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

[Mukesh Kumar Chaurasiya]

On Thu, Sep 10, 2026 at 09:36:34AM +0200, Christophe Leroy (CS GROUP) wrote:
> 
> 
> 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
> 
Hey Thanks for pointing it out.

Yeah the assuption to always use 1 shouldn't be there. It should come as
an argument. Will fix this and send out a new revision.

Regards,
Mukesh
> > 
> > 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
>