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[v2,4/5] sh: Emulate two-byte cmpxchg

Message ID 20260916200215.21774-5-brads@mainlining.org
State New
Headers show
Series Add two-byte cmpxchg emulation and wire it into the architectures | expand

Commit Message

Bradley Morgan Sept. 16, 2026, 8:02 p.m. UTC 
SH has no byte or halfword atomic memory operations, so the __cmpxchg()
switch routes case 1 through cmpxchg_emu_u8() and lets case 2 fall
through to __cmpxchg_called_with_bad_pointer(), which is declared but
never defined, so a two-byte cmpxchg() fails at link time. Route case
2 through the new cmpxchg_emu_u16(), which takes natural u16
arguments, so the unsigned long old and new narrow at the function
boundary.

Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Bradley Morgan <brads@mainlining.org>
---
 arch/sh/include/asm/cmpxchg.h | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
index 1e5dc5ccf7bf..477d3025a441 100644
--- a/arch/sh/include/asm/cmpxchg.h
+++ b/arch/sh/include/asm/cmpxchg.h
@@ -59,6 +59,8 @@  static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old,
 	switch (size) {
 	case 1:
 		return cmpxchg_emu_u8(ptr, old, new);
+	case 2:
+		return cmpxchg_emu_u16(ptr, old, new);
 	case 4:
 		return __cmpxchg_u32(ptr, old, new);
 	}