linux-kernel - Re: [PATCH net-next v2] page_pool: fix build on powerpc with GCC 14

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Message-ID: <87jzffq9ge.fsf@mail.lhotse>
Date: Sat, 14 Sep 2024 12:02:09 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Mina Almasry <almasrymina@...gle.com>, Jesper Dangaard Brouer
 <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon
 Horman <horms@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>, Linux
 Next Mailing List <linux-next@...r.kernel.org>, Arnd Bergmann
 <arnd@...db.de>, "linuxppc-dev@...ts.ozlabs.org"
 <linuxppc-dev@...ts.ozlabs.org>, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH net-next v2] page_pool: fix build on powerpc with GCC 14

Mina Almasry <almasrymina@...gle.com> writes:
> Building net-next with powerpc with GCC 14 compiler results in this
> build error:
>
> /home/sfr/next/tmp/ccuSzwiR.s: Assembler messages:
> /home/sfr/next/tmp/ccuSzwiR.s:2579: Error: operand out of domain (39 is
> not a multiple of 4)
> make[5]: *** [/home/sfr/next/next/scripts/Makefile.build:229:
> net/core/page_pool.o] Error 1
>
> Root caused in this thread:
> https://lore.kernel.org/netdev/913e2fbd-d318-4c9b-aed2-4d333a1d5cf0@cs-soprasteria.com/

Sorry I'm late to this, the original report wasn't Cc'ed to linuxppc-dev :D

I think this is a bug in the arch/powerpc inline asm constraints.

Can you try the patch below, it fixes the build error for me.

I'll run it through some boot tests and turn it into a proper patch over
the weekend.

cheers

diff --git a/arch/powerpc/include/asm/atomic.h b/arch/powerpc/include/asm/atomic.h
index 5bf6a4d49268..0e41c1da82dd 100644
--- a/arch/powerpc/include/asm/atomic.h
+++ b/arch/powerpc/include/asm/atomic.h
@@ -23,6 +23,12 @@
 #define __atomic_release_fence()					\
 	__asm__ __volatile__(PPC_RELEASE_BARRIER "" : : : "memory")

+#ifdef CONFIG_CC_IS_CLANG
+#define DS_FORM_CONSTRAINT "Z<>"
+#else
+#define DS_FORM_CONSTRAINT "YZ<>"
+#endif
+
 static __inline__ int arch_atomic_read(const atomic_t *v)
 {
 	int t;
@@ -197,7 +203,7 @@ static __inline__ s64 arch_atomic64_read(const atomic64_t *v)
 	if (IS_ENABLED(CONFIG_PPC_KERNEL_PREFIXED))
 		__asm__ __volatile__("ld %0,0(%1)" : "=r"(t) : "b"(&v->counter));
 	else
-		__asm__ __volatile__("ld%U1%X1 %0,%1" : "=r"(t) : "m<>"(v->counter));
+		__asm__ __volatile__("ld%U1%X1 %0,%1" : "=r"(t) : DS_FORM_CONSTRAINT (v->counter));

 	return t;
 }
@@ -208,7 +214,7 @@ static __inline__ void arch_atomic64_set(atomic64_t *v, s64 i)
 	if (IS_ENABLED(CONFIG_PPC_KERNEL_PREFIXED))
 		__asm__ __volatile__("std %1,0(%2)" : "=m"(v->counter) : "r"(i), "b"(&v->counter));
 	else
-		__asm__ __volatile__("std%U0%X0 %1,%0" : "=m<>"(v->counter) : "r"(i));
+		__asm__ __volatile__("std%U0%X0 %1,%0" : "=" DS_FORM_CONSTRAINT (v->counter) : "r"(i));
 }

 #define ATOMIC64_OP(op, asm_op)						\