powerpc/atomic: Use YZ constraints for DS-form instructions

The 'ld' and 'std' instructions require a 4-byte aligned displacement
because they are DS-form instructions. But the "m" asm constraint
doesn't enforce that.

That can lead to build errors if the compiler chooses a non-aligned
displacement, as seen with GCC 14:

  /tmp/ccuSzwiR.s: Assembler messages:
  /tmp/ccuSzwiR.s:2579: Error: operand out of domain (39 is not a multiple of 4)
  make[5]: *** [scripts/Makefile.build:229: net/core/page_pool.o] Error 1

Dumping the generated assembler shows:

  ld 8,39(8)       # MEM[(const struct atomic64_t *)_29].counter, t

Use the YZ constraints to tell the compiler either to generate a DS-form
displacement, or use an X-form instruction, either of which prevents the
build error.

See commit 2d43cc7 ("powerpc/uaccess: Fix build errors seen with
GCC 13/14") for more details on the constraint letters.

Fixes: 9f0cbea ("[POWERPC] Implement atomic{, 64}_{read, write}() without volatile")
Cc: stable@vger.kernel.org # v2.6.24+
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/all/20240913125302.0a06b4c7@canb.auug.org.au
Tested-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240916120510.2017749-1-mpe@ellerman.id.au

arch/powerpc/include/asm/asm-compat.h

@@ -37,6 +37,12 @@
 #define STDX_BE	stringify_in_c(stdbrx)
 #endif
 
+#ifdef CONFIG_CC_IS_CLANG
+#define DS_FORM_CONSTRAINT "Z<>"
+#else
+#define DS_FORM_CONSTRAINT "YZ<>"
+#endif
+
 #else /* 32-bit */
 
 /* operations for longs and pointers */

arch/powerpc/include/asm/atomic.h

@@ -11,6 +11,7 @@
 #include <asm/cmpxchg.h>
 #include <asm/barrier.h>
 #include <asm/asm-const.h>
+#include <asm/asm-compat.h>
 
 /*
  * Since *_return_relaxed and {cmp}xchg_relaxed are implemented with
@@ -197,7 +198,7 @@ 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 +209,7 @@ 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)						\

arch/powerpc/include/asm/uaccess.h

@@ -6,6 +6,7 @@
 #include <asm/page.h>
 #include <asm/extable.h>
 #include <asm/kup.h>
+#include <asm/asm-compat.h>
 
 #ifdef __powerpc64__
 /* We use TASK_SIZE_USER64 as TASK_SIZE is not constant */
@@ -92,12 +93,6 @@ __pu_failed:							\
 		: label)
 #endif
 
-#ifdef CONFIG_CC_IS_CLANG
-#define DS_FORM_CONSTRAINT "Z<>"
-#else
-#define DS_FORM_CONSTRAINT "YZ<>"
-#endif
-
 #ifdef __powerpc64__
 #ifdef CONFIG_PPC_KERNEL_PREFIXED
 #define __put_user_asm2_goto(x, ptr, label)			\