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

Subsystems: linux for powerpc (32-bit and 64-bit), the rest

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6 messages, 4 authors, 21d ago · open the first message on its own page

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

From: Mukesh Kumar Chaurasiya (IBM) <hidden>
Date: 2026-08-19 08:48:59 

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 <redacted>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
---
 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
-- 
2.55.0

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

From: Miguel Ojeda <hidden>
Date: 2026-08-19 10:02:30 

On Wed, Aug 19, 2026 at 10:48 AM Mukesh Kumar Chaurasiya (IBM)
[off-list ref] wrote:
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 <redacted>
Should this be Reported-by?

In addition, probably we want a Link to the original report, and a Fixes tag.

Ideally, please include the error message in the commit message -- it
helps to triaging and also to search it later on etc.

Thanks!

Cheers,
Miguel

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

From: Mukesh Kumar Chaurasiya <hidden>
Date: 2026-08-19 10:42:30 

On Wed, Aug 19, 2026 at 12:02:01PM +0200, Miguel Ojeda wrote:
On Wed, Aug 19, 2026 at 10:48 AM Mukesh Kumar Chaurasiya (IBM)
[off-list ref] wrote:
quoted
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 <redacted>
Should this be Reported-by?
The change itself is suggested by Tomonori so i was not sure.

Yeah there should be

Reported-by: Link Mauve <redacted>
Closes: https://lore.kernel.org/all/anG67Q6Y59kDqh-c@desktop
Fixes: 73b741adb264 ("rust: Add PowerPC support")
In addition, probably we want a Link to the original report, and a Fixes tag.

Ideally, please include the error message in the commit message -- it
helps to triaging and also to search it later on etc.
Sure i'll add the error to the commit message and send out a new
revision.


Thanks!

Cheers,
Miguel
Thanks for the quick review.

Regards,
Mukesh

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

From: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
Date: 2026-08-19 11:51:05 


Le 19/08/2026 à 10:48, Mukesh Kumar Chaurasiya (IBM) a écrit :
quoted hunk
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 <redacted>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
---
  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__ */
Sorry, I still don't understand. The only place the new macro is used is a .S file (namely rust/kernel/generated_arch_warn_asm.rs.S), and the change this patch implements is inside a #if !__ASSEMBLER__.

What am I missing ?

Christophe
quoted hunk
-/* _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





  

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

    

      From: Mukesh Kumar Chaurasiya <hidden>

      Date: 2026-08-20 06:49:59 
    

  

  
On Wed, Aug 19, 2026 at 01:50:43PM +0200, Christophe Leroy (CS GROUP) wrote:

Le 19/08/2026 à 10:48, Mukesh Kumar Chaurasiya (IBM) a écrit :
quoted
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 <redacted>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
---
  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__ */
Sorry, I still don't understand. The only place the new macro is used is a
.S file (namely rust/kernel/generated_arch_warn_asm.rs.S), and the change
this patch implements is inside a #if !__ASSEMBLER__.

What am I missing ?

Christophe
Hey Christophe,

The code calling ARCH_WARN_ASM is a .rs.S file that goes through the C
preprocessor as part of the Rust build machinery.

The intended mechanism is essentially

generated_arch_warn_asm.rs.S
          |
          v
         CPP
          |
          | includes <linux/bug.h>
          |
          v
ARCH_WARN_ASM(...) gets expanded
          |
          v
Rust source containing the generated assembly string

The patch therefore needs ARCH_WARN_ASM in the non-__ASSEMBLER__ section,
because that section is where the macros intended for C preprocessing
are defined.

The thing is .rs.S is not using ARCH_WARN_ASM as an assembler-time macro,
it is using the C preprocessor to expand ARCH_WARN_ASM before the
Rust/assembly processing stage.

This is my understanding of things, if i am wrong somewhere maybe
someone can clarify.

Regards,
Mukesh


[...]






  

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

    

      From: R Nageswara Sastry <hidden>

      Date: 2026-09-17 10:08:09 
    

  

  
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 <redacted>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Tested on PowerPC LPAR + 7.3.0-rc3 by creating a small .rs module to

trigger ARCH_WARN_ASM.

Tested-by: R Nageswara Sastry <redacted>

quoted hunk
---
  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






    
  

  
    

      

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