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 2d43cc701b96 ("powerpc/uaccess: Fix build errors seen with
GCC 13/14") for more details on the constraint letters.
Fixes: 9f0cbea0d8cc ("[POWERPC] Implement atomic{, 64}_{read, write}() without volatile")
Cc: stable@xxxxxxxxxxxxxxx # v2.6.24+
Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/20240913125302.0a06b4c7@xxxxxxxxxxxxxxxx
Tested-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Reviewed-by: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20240916120510.2017749-1-mpe@xxxxxxxxxxxxxx
diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h
index b0b209c1df50..f48e644900a2 100644
--- a/arch/powerpc/include/asm/asm-compat.h
+++ b/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 */
diff --git a/arch/powerpc/include/asm/atomic.h b/arch/powerpc/include/asm/atomic.h
index 5bf6a4d49268..d1ea554c33ed 100644
--- a/arch/powerpc/include/asm/atomic.h
+++ b/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) \
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index fd594bf6c6a9..4f5a46a77fa2 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/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) \
