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* [PATCH 5.10.y 5.15.y 6.1.y 6.6.y 6.12.y 6.18.y 6.19.y] ARM: clean up the memset64() C wrapper
@ 2026-02-25 11:35 Thomas Weißschuh
  2026-02-25 14:36 ` Greg KH
  0 siblings, 1 reply; 6+ messages in thread
From: Thomas Weißschuh @ 2026-02-25 11:35 UTC (permalink / raw)
  To: stable; +Cc: Matthew Wilcox, Thomas Weißschuh, Linus Torvalds,
	Ben Hutchings

[ Upstream commit b52343d1cb47bb27ca32a3f4952cc2fd3cd165bf ]

The current logic to split the 64-bit argument into its 32-bit halves is
byte-order specific and a bit clunky.  Use a union instead which is
easier to read and works in all cases.

GCC still generates the same machine code.

While at it, rename the arguments of the __memset64() prototype to
actually reflect their semantics.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Ben Hutchings <ben@decadent.org.uk> # for -stable
Link: https://lore.kernel.org/all/1a11526ae3d8664f705b541b8d6ea57b847b49a8.camel@decadent.org.uk/
Suggested-by: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/ # for -stable
Link: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/
---
Hi stable team,

unfortunately the backports of commit 23ea2a4c7232 ("ARM: 9468/1: fix
memset64() on big-endian") does not work on 5.10 and 5.15 as
CONFIG_CPU_LITTLE_ENDIAN does not exist there, effectively breaking memset64()
on little-endian. Please use this variant instead which always works.
For consistency I prefer to have it backported to all versions.
---
 arch/arm/include/asm/string.h | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
index b5ad23acb303..369781ec5511 100644
--- a/arch/arm/include/asm/string.h
+++ b/arch/arm/include/asm/string.h
@@ -33,13 +33,17 @@ static inline void *memset32(uint32_t *p, uint32_t v, __kernel_size_t n)
 }
 
 #define __HAVE_ARCH_MEMSET64
-extern void *__memset64(uint64_t *, uint32_t low, __kernel_size_t, uint32_t hi);
+extern void *__memset64(uint64_t *, uint32_t first, __kernel_size_t, uint32_t second);
 static inline void *memset64(uint64_t *p, uint64_t v, __kernel_size_t n)
 {
-	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
-		return __memset64(p, v, n * 8, v >> 32);
-	else
-		return __memset64(p, v >> 32, n * 8, v);
+	union {
+		uint64_t val;
+		struct {
+			uint32_t first, second;
+		};
+	} word = { .val = v };
+
+	return __memset64(p, word.first, n * 8, word.second);
 }
 
 #endif

---
base-commit: 3e2558088a1a3dc941eec8edafd002758ae97d77
change-id: 20260225-arm-memset64-stable-dc00bb0bb1af

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@linutronix.de>


^ permalink raw reply related	[flat|nested] 6+ messages in thread

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Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2026-02-25 11:35 [PATCH 5.10.y 5.15.y 6.1.y 6.6.y 6.12.y 6.18.y 6.19.y] ARM: clean up the memset64() C wrapper Thomas Weißschuh
2026-02-25 14:36 ` Greg KH
2026-02-25 15:08   ` Thomas Weißschuh
2026-02-25 15:14     ` Greg KH
2026-02-25 16:03       ` Thomas Weißschuh
2026-02-25 16:18         ` Greg KH

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