s390/percpu: Fix MVIY_PERCPU() with older binutils

[PATCH] s390/percpu: Fix MVIY_PERCPU() with older binutils

Posted by Karl Mehltretter 1 month, 2 weeks ago

Commit a737737cdb9c ("s390/percpu: Infrastructure for more efficient
this_cpu operations") introduced MVIY_PERCPU(), which stringifies
arguments that are already C string literals. This generates an
assembler macro invocation with whitespace-separated quoted arguments:

  GEN_MVIY "459712" "%r3"

GNU as versions prior to binutils 2.39 drop the separating whitespace
between quoted macro arguments during input scrubbing. They
consequently parse the invocation as a single argument and emit
repeated warnings:

  Warning: missing closing `"'

The .ifc in GEN_MVIY never matches and GNU as exits successfully
without emitting the mviy instruction. As a result, the interrupted
per-CPU sequence is not marked in lowcore and the exception return
path cannot repair the per-CPU address register after migration.

All MVIY_PERCPU() callers pass C string literals. Use them directly
and separate the assembler macro arguments with an explicit comma. The
resulting invocation is:

  GEN_MVIY 459712, %r3

This form is unambiguous for GNU as and LLVM's integrated assembler.
This behavior was fixed in GNU as from binutils 2.39, but Linux
supports binutils 2.30.

Fixes: a737737cdb9c ("s390/percpu: Infrastructure for more efficient this_cpu operations")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
 arch/s390/include/asm/percpu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h
index 1d955dd0defa3..feb58acf87d69 100644
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -107,8 +107,8 @@
 	"	.endif\n"							\
 	".endr\n"								\
 	".endm\n"								\
-	ALTERNATIVE("GEN_MVIY " __stringify(disp)    " " __stringify(reg) "\n",	\
-		    "GEN_MVIY " __stringify(dispalt) " " __stringify(reg) "\n",	\
+	ALTERNATIVE("GEN_MVIY " disp    ", " reg "\n",				\
+		    "GEN_MVIY " dispalt ", " reg "\n",				\
 		    ALT_FEATURE(MFEATURE_LOWCORE))				\
 	".purgem GEN_MVIY\n"
 
-- 
2.53.0

Re: [PATCH] s390/percpu: Fix MVIY_PERCPU() with older binutils

Posted by Vasily Gorbik 1 month, 2 weeks ago

On Wed, Aug 12, 2026 at 10:30:36PM +0200, Karl Mehltretter wrote:
> Commit a737737cdb9c ("s390/percpu: Infrastructure for more efficient
> this_cpu operations") introduced MVIY_PERCPU(), which stringifies
> arguments that are already C string literals. This generates an
> assembler macro invocation with whitespace-separated quoted arguments:
> 
>   GEN_MVIY "459712" "%r3"
> 
> GNU as versions prior to binutils 2.39 drop the separating whitespace
> between quoted macro arguments during input scrubbing. They
> consequently parse the invocation as a single argument and emit
> repeated warnings:
> 
>   Warning: missing closing `"'
> 
> The .ifc in GEN_MVIY never matches and GNU as exits successfully
> without emitting the mviy instruction. As a result, the interrupted
> per-CPU sequence is not marked in lowcore and the exception return
> path cannot repair the per-CPU address register after migration.
> 
> All MVIY_PERCPU() callers pass C string literals. Use them directly
> and separate the assembler macro arguments with an explicit comma. The
> resulting invocation is:
> 
>   GEN_MVIY 459712, %r3
> 
> This form is unambiguous for GNU as and LLVM's integrated assembler.
> This behavior was fixed in GNU as from binutils 2.39, but Linux
> supports binutils 2.30.
> 
> Fixes: a737737cdb9c ("s390/percpu: Infrastructure for more efficient this_cpu operations")
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
> ---
>  arch/s390/include/asm/percpu.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Applied, thank you!

Re: [PATCH] s390/percpu: Fix MVIY_PERCPU() with older binutils

Posted by Heiko Carstens 1 month, 2 weeks ago

On Wed, Aug 12, 2026 at 10:30:36PM +0200, Karl Mehltretter wrote:
> Commit a737737cdb9c ("s390/percpu: Infrastructure for more efficient
> this_cpu operations") introduced MVIY_PERCPU(), which stringifies
> arguments that are already C string literals. This generates an
> assembler macro invocation with whitespace-separated quoted arguments:
> 
>   GEN_MVIY "459712" "%r3"
> 
> GNU as versions prior to binutils 2.39 drop the separating whitespace
> between quoted macro arguments during input scrubbing. They
> consequently parse the invocation as a single argument and emit
> repeated warnings:
> 
>   Warning: missing closing `"'
> 
> The .ifc in GEN_MVIY never matches and GNU as exits successfully
> without emitting the mviy instruction. As a result, the interrupted
> per-CPU sequence is not marked in lowcore and the exception return
> path cannot repair the per-CPU address register after migration.
> 
> All MVIY_PERCPU() callers pass C string literals. Use them directly
> and separate the assembler macro arguments with an explicit comma. The
> resulting invocation is:
> 
>   GEN_MVIY 459712, %r3
> 
> This form is unambiguous for GNU as and LLVM's integrated assembler.
> This behavior was fixed in GNU as from binutils 2.39, but Linux
> supports binutils 2.30.
> 
> Fixes: a737737cdb9c ("s390/percpu: Infrastructure for more efficient this_cpu operations")
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
> ---
>  arch/s390/include/asm/percpu.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Thanks a lot. I'm about to change this code anyway. It seems it should better
error out instead of generating incorrect code (even if there is a warning).

Vasily, could you add

Cc: stable@vger.kernel.org

please?

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>