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[PATCH V6] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

Mukesh Kumar Chaurasiya (IBM) posted 1 patch 2 days, 10 hours ago 
arch/powerpc/include/asm/bug.h | 46 ++++++++++++++++++----------------
1 file changed, 25 insertions(+), 21 deletions(-)
[PATCH V6] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support
Posted by Mukesh Kumar Chaurasiya (IBM) 2 days, 10 hours ago 
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
```

To add ARCH_WARN_ASM, _EMIT_BUG_ENTRY first needs to be refactored.
The old definition was a bare macro with no parameters, relying on
positional asm operand references (%0-%3), hardcoding the backward
reference to local label 1b, and including .org/.previous directives
inline. That made it impossible to compose as a plain string outside of
an asm operand context, and left an invisible contract that callers must
always emit their trap at label 1:.

Refactor _EMIT_BUG_ENTRY to take explicit (bug_entry, trap, file, line, flags)
string arguments via string concatenation. This removes the dependency
on asm operand numbering and makes the labels an explicit argument,
so the caller's intent is visible at the call site and a future caller
using a different label cannot silently produce a wrong bug table entry.

Move the .org and .previous directives out of _EMIT_BUG_ENTRY and into
each call site, so BUG_ENTRY() can still pass sizeof(struct bug_entry)
as an asm operand while ARCH_WARN_ASM can supply its own size string
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.

Reported-by: FUJITA Tomonori <tomo@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@gmail.com>
---
Changelog:
V5 -> V6:
 - Dropped KUit tests from this series. It will be sent separately.
V5: https://lore.kernel.org/all/20260915090453.1227034-1-mkchauras@gmail.com/

V4 -> V5:
 - Fixed a build error with DEBUG_BUGVERBOSE=n
 - Added a label for bug entry
V4: https://lore.kernel.org/all/20260912065902.24017-1-mkchauras@gmail.com/

V3 -> V4:
 - Fix Label with appending b at end
 - Add KUnit test patch
 - Tested on ppc64le pseries: pass:5 fail:0 skip:0
 - Tested on ppc32 QEMU mac99 G4: pass:5 fail:0 skip:0
 - Tested on ppc64le QEMU pseries: pass:5 fail:0 skip:0
V3: https://lore.kernel.org/all/20260910100801.2159785-2-mkchauras@gmail.com

V2 -> V3:
 - Add label argument in _EMIT_BUG_ENTRY
V2: https://lore.kernel.org/all/20260910071252.1950488-2-mkchauras@gmail.com

V1 -> V2:
 - commit message now has error, fixes tag and closes tag
V1: https://lore.kernel.org/all/20260819084825.969116-1-mkchauras@gmail.com

 arch/powerpc/include/asm/bug.h | 46 ++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index 0db48977c70c..bf31ee1e902a 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				\
-	".section __bug_table,\"aw\"\n"		\
-	"2:	.4byte 1b - .\n"		\
-	"	.4byte %0 - .\n"		\
-	"	.short %1, %2\n"		\
-	".org 2b+%3\n"				\
-	".previous\n"
+#define _EMIT_BUG_ENTRY(bug_entry, trap, file, line, flags)	\
+	".section __bug_table,\"aw\"\n"				\
+	#bug_entry ":	.4byte " #trap " - .\n"			\
+	"		.4byte " file " - .\n"			\
+	"		.short " line ", " flags "\n"
 #else
-#define _EMIT_BUG_ENTRY				\
-	".section __bug_table,\"aw\"\n"		\
-	"2:	.4byte 1b - .\n"		\
-	"	.short %2\n"			\
-	".org 2b+%3\n"				\
-	".previous\n"
+#define _EMIT_BUG_ENTRY(bug_entry, trap, file, line, flags)	\
+	".section __bug_table,\"aw\"\n"				\
+	#bug_entry ":	.4byte " #trap " - .\n"			\
+	"		.short " flags "\n"
 #endif
 
-#define BUG_ENTRY(cond_str, insn, flags, ...)		\
-	__asm__ __volatile__(				\
-		"1:	" insn "\n"			\
-		_EMIT_BUG_ENTRY				\
+#define BUG_ENTRY(cond_str, insn, flags, ...)			\
+	__asm__ __volatile__(					\
+		"1:	" insn "\n"				\
+		_EMIT_BUG_ENTRY(2, 1b, "%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)),	\
+		  "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(2, 1b, 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
-- 
2.55.0
Re: [PATCH V6] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support
Posted by Christophe Leroy (CS GROUP) 3 hours ago 

Le 22/09/2026 à 07:43, 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

I'm a bit puzzled by the macro name. The name ARCH_WARN_ASM suggests 
that it is used for warnings like WARN() and/or WARN_ON(). Which means 
it should include flags BUGFLAG_WARNING and BUGFLAG_TAINT(TAINT_WARN).

Also I have the feeling that it only handles WARN().
WARN_ON() seems to have been forgotten.

Christophe

> ```
> 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
> ```
> 
> To add ARCH_WARN_ASM, _EMIT_BUG_ENTRY first needs to be refactored.
> The old definition was a bare macro with no parameters, relying on
> positional asm operand references (%0-%3), hardcoding the backward
> reference to local label 1b, and including .org/.previous directives
> inline. That made it impossible to compose as a plain string outside of
> an asm operand context, and left an invisible contract that callers must
> always emit their trap at label 1:.
> 
> Refactor _EMIT_BUG_ENTRY to take explicit (bug_entry, trap, file, line, flags)
> string arguments via string concatenation. This removes the dependency
> on asm operand numbering and makes the labels an explicit argument,
> so the caller's intent is visible at the call site and a future caller
> using a different label cannot silently produce a wrong bug table entry.
> 
> Move the .org and .previous directives out of _EMIT_BUG_ENTRY and into
> each call site, so BUG_ENTRY() can still pass sizeof(struct bug_entry)
> as an asm operand while ARCH_WARN_ASM can supply its own size string
> 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.
> 
> Reported-by: FUJITA Tomonori <tomo@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@gmail.com>
> ---
> Changelog:
> V5 -> V6:
>   - Dropped KUit tests from this series. It will be sent separately.
> V5: https://lore.kernel.org/all/20260915090453.1227034-1-mkchauras@gmail.com/
> 
> V4 -> V5:
>   - Fixed a build error with DEBUG_BUGVERBOSE=n
>   - Added a label for bug entry
> V4: https://lore.kernel.org/all/20260912065902.24017-1-mkchauras@gmail.com/
> 
> V3 -> V4:
>   - Fix Label with appending b at end
>   - Add KUnit test patch
>   - Tested on ppc64le pseries: pass:5 fail:0 skip:0
>   - Tested on ppc32 QEMU mac99 G4: pass:5 fail:0 skip:0
>   - Tested on ppc64le QEMU pseries: pass:5 fail:0 skip:0
> V3: https://lore.kernel.org/all/20260910100801.2159785-2-mkchauras@gmail.com
> 
> V2 -> V3:
>   - Add label argument in _EMIT_BUG_ENTRY
> V2: https://lore.kernel.org/all/20260910071252.1950488-2-mkchauras@gmail.com
> 
> V1 -> V2:
>   - commit message now has error, fixes tag and closes tag
> V1: https://lore.kernel.org/all/20260819084825.969116-1-mkchauras@gmail.com
> 
>   arch/powerpc/include/asm/bug.h | 46 ++++++++++++++++++----------------
>   1 file changed, 25 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 0db48977c70c..bf31ee1e902a 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				\
> -	".section __bug_table,\"aw\"\n"		\
> -	"2:	.4byte 1b - .\n"		\
> -	"	.4byte %0 - .\n"		\
> -	"	.short %1, %2\n"		\
> -	".org 2b+%3\n"				\
> -	".previous\n"
> +#define _EMIT_BUG_ENTRY(bug_entry, trap, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"				\
> +	#bug_entry ":	.4byte " #trap " - .\n"			\
> +	"		.4byte " file " - .\n"			\
> +	"		.short " line ", " flags "\n"
>   #else
> -#define _EMIT_BUG_ENTRY				\
> -	".section __bug_table,\"aw\"\n"		\
> -	"2:	.4byte 1b - .\n"		\
> -	"	.short %2\n"			\
> -	".org 2b+%3\n"				\
> -	".previous\n"
> +#define _EMIT_BUG_ENTRY(bug_entry, trap, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"				\
> +	#bug_entry ":	.4byte " #trap " - .\n"			\
> +	"		.short " flags "\n"
>   #endif
>   
> -#define BUG_ENTRY(cond_str, insn, flags, ...)		\
> -	__asm__ __volatile__(				\
> -		"1:	" insn "\n"			\
> -		_EMIT_BUG_ENTRY				\
> +#define BUG_ENTRY(cond_str, insn, flags, ...)			\
> +	__asm__ __volatile__(					\
> +		"1:	" insn "\n"				\
> +		_EMIT_BUG_ENTRY(2, 1b, "%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)),	\
> +		  "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(2, 1b, 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

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