[PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Mukesh Kumar Chaurasiya (IBM)]

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 (label, file, line, flags)
string arguments via string concatenation. This removes the dependency
on asm operand numbering and makes the trap label 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.

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@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:
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 | 36 +++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
+	".section __bug_table,\"aw\"\n"			\
+	"2:	.4byte " label "b - .\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(label, file, line, flags)	\
+	".section __bug_table,\"aw\"\n"			\
+	"2:	.4byte " label "b - .\n"		\
+	"	.short " flags "\n"
 #endif
 
 #define BUG_ENTRY(cond_str, insn, flags, ...)		\
 	__asm__ __volatile__(				\
 		"1:	" insn "\n"			\
-		_EMIT_BUG_ENTRY				\
+		_EMIT_BUG_ENTRY("1", "%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("1", 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


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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Gary Guo]

On Thu Sep 10, 2026 at 11:08 AM BST, 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 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}"))

I think we probably want to catch this earlier by have something like

#ifndef ARCH_WARN_ASM
#error "ARCH_WARM_ASM is not defined"
#endif

in generated_arch_warn_asm.rs.S.

>     |                            ^^^^^^^^^^^^^ 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 (label, file, line, flags)
> string arguments via string concatenation. This removes the dependency
> on asm operand numbering and makes the trap label 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.
>
> 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@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:
> 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 | 36 +++++++++++++++++++---------------
>  1 file changed, 20 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"			\
> +	"2:	.4byte " label "b - .\n"		\

"b" is part of the label. "1b" itself is a label and "1" is just an integer.

If the code uses

    _EMIT_BUG_ENTRY(..)
    "1: ..."

then the correct label would be "1f".

Best,
Gary


> +	"	.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(label, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"			\
> +	"2:	.4byte " label "b - .\n"		\
> +	"	.short " flags "\n"
>  #endif
>  
>  #define BUG_ENTRY(cond_str, insn, flags, ...)		\
>  	__asm__ __volatile__(				\
>  		"1:	" insn "\n"			\
> -		_EMIT_BUG_ENTRY				\
> +		_EMIT_BUG_ENTRY("1", "%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("1", 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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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[FUJITA Tomonori]

On Thu, 10 Sep 2026 13:05:27 +0100
"Gary Guo" <gary@garyguo.net> wrote:

> On Thu Sep 10, 2026 at 11:08 AM BST, 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 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}"))
> 
> I think we probably want to catch this earlier by have something like
> 
> #ifndef ARCH_WARN_ASM
> #error "ARCH_WARM_ASM is not defined"
> #endif
> 
> in generated_arch_warn_asm.rs.S.

Good idea.

One thing needs to be fixed first. arm and loongarch do not define
ARCH_WARN_ASM. rust/kernel/bug.rs uses bindings::WARN_ON() on those
architectures, so it never includes generated_arch_warn_asm.rs. But
rust/Makefile still generates the file for them. With #error, their
builds would break.

I think we should add a condition to rust/Makefile to stop generating
the file for arm and loongarch. Then #error can be unconditional.

Does that sound reasonable? I can send patches.


>>  arch/powerpc/include/asm/bug.h | 36 +++++++++++++++++++---------------
>>  1 file changed, 20 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
>> index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
>> +	".section __bug_table,\"aw\"\n"			\
>> +	"2:	.4byte " label "b - .\n"		\
> 
> "b" is part of the label. "1b" itself is a label and "1" is just an integer.
> 
> If the code uses
> 
>     _EMIT_BUG_ENTRY(..)
>     "1: ..."
> 
> then the correct label would be "1f".

Agreed.

I think keeping the label fixed, as v2 did, would be fine too. x86,
arm64 and riscv all hardcode it. A comment that says the caller must
put the trap at 1: might be enough.


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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Christophe Leroy (CS GROUP)]

Le 10/09/2026 à 12:08, 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
> ```
> 
> 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 (label, file, line, flags)
> string arguments via string concatenation. This removes the dependency
> on asm operand numbering and makes the trap label 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.
> 
> 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@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:
> 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 | 36 +++++++++++++++++++---------------
>   1 file changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"			\
> +	"2:	.4byte " label "b - .\n"		\

Ah, you left the b here. The label is 1b which mean "the first 1: you 
find going backward". Could as well be "1f" instead meaning "the first 
1: you find going forward".

So I think you should use 1b or 1f as the label, not just 1.

I would also try to use #label to stringigy the label in order to avoid 
having to put the arguments into quotes (untested), same for other ones.

Cdlt
Christophe

> +	"	.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(label, file, line, flags)	\
> +	".section __bug_table,\"aw\"\n"			\
> +	"2:	.4byte " label "b - .\n"		\
> +	"	.short " flags "\n"
>   #endif
>   
>   #define BUG_ENTRY(cond_str, insn, flags, ...)		\
>   	__asm__ __volatile__(				\
>   		"1:	" insn "\n"			\
> -		_EMIT_BUG_ENTRY				\
> +		_EMIT_BUG_ENTRY("1", "%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("1", 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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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Mukesh Kumar Chaurasiya]

On Thu, Sep 10, 2026 at 01:05:27PM +0100, Gary Guo wrote:
> On Thu Sep 10, 2026 at 11:08 AM BST, 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 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}"))
> 
> I think we probably want to catch this earlier by have something like
> 
> #ifndef ARCH_WARN_ASM
> #error "ARCH_WARM_ASM is not defined"
> #endif
> 
> in generated_arch_warn_asm.rs.S.
> 
Hey Gary,

Sounds good.
[...]
> >
> >  arch/powerpc/include/asm/bug.h | 36 +++++++++++++++++++---------------
> >  1 file changed, 20 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> > index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
> > +	".section __bug_table,\"aw\"\n"			\
> > +	"2:	.4byte " label "b - .\n"		\
> 
> "b" is part of the label. "1b" itself is a label and "1" is just an integer.
> 
> If the code uses
> 
>     _EMIT_BUG_ENTRY(..)
>     "1: ..."
> 
> then the correct label would be "1f".
> 
> Best,
> Gary
> 
Thanks, I missed that part.

Will fix it and send it out.

Regards,
Mukesh
> 
[...]

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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Mukesh Kumar Chaurasiya]

On Thu, Sep 10, 2026 at 10:24:17PM +0900, FUJITA Tomonori wrote:
> On Thu, 10 Sep 2026 13:05:27 +0100
> "Gary Guo" <gary@garyguo.net> wrote:
> 
> > On Thu Sep 10, 2026 at 11:08 AM BST, 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 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}"))
> > 
> > I think we probably want to catch this earlier by have something like
> > 
> > #ifndef ARCH_WARN_ASM
> > #error "ARCH_WARM_ASM is not defined"
> > #endif
> > 
> > in generated_arch_warn_asm.rs.S.
> 
> Good idea.
> 
> One thing needs to be fixed first. arm and loongarch do not define
> ARCH_WARN_ASM. rust/kernel/bug.rs uses bindings::WARN_ON() on those
> architectures, so it never includes generated_arch_warn_asm.rs. But
> rust/Makefile still generates the file for them. With #error, their
> builds would break.
> 
> I think we should add a condition to rust/Makefile to stop generating
> the file for arm and loongarch. Then #error can be unconditional.
> 
> Does that sound reasonable? I can send patches.
> 
Hey,

Sounds fair to me.
> 
> >>  arch/powerpc/include/asm/bug.h | 36 +++++++++++++++++++---------------
> >>  1 file changed, 20 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> >> index 0db48977c70c..df2183c35945 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(label, file, line, flags)	\
> >> +	".section __bug_table,\"aw\"\n"			\
> >> +	"2:	.4byte " label "b - .\n"		\
> > 
> > "b" is part of the label. "1b" itself is a label and "1" is just an integer.
> > 
> > If the code uses
> > 
> >     _EMIT_BUG_ENTRY(..)
> >     "1: ..."
> > 
> > then the correct label would be "1f".
> 
> Agreed.
> 
> I think keeping the label fixed, as v2 did, would be fine too. x86,
> arm64 and riscv all hardcode it. A comment that says the caller must
> put the trap at 1: might be enough.
> 
Enforcing the label would be a better idea so that we can avoid
mistakes. I'll fix these and send out a new one.

Regards,
Mukesh

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Re: [PATCH V3] powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust support

[Mukesh Kumar Chaurasiya]

On Thu, Sep 10, 2026 at 05:08:48PM +0200, Christophe Leroy (CS GROUP) wrote:
> 
[...]
> > -/* _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(label, file, line, flags)	\
> > +	".section __bug_table,\"aw\"\n"			\
> > +	"2:	.4byte " label "b - .\n"		\
> 
> Ah, you left the b here. The label is 1b which mean "the first 1: you find
> going backward". Could as well be "1f" instead meaning "the first 1: you
> find going forward".
> 
> So I think you should use 1b or 1f as the label, not just 1.
Hey Christophe,

Thanks for the clear explanation, this helps a lot.
> 
> I would also try to use #label to stringigy the label in order to avoid
> having to put the arguments into quotes (untested), same for other ones.
> 
Ohk, letme try that.

> Cdlt
> Christophe
> 

Regards,
Mukesh
[...]

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