diff mbox series

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

Message ID 20260916200215.21774-6-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 
Xtensa has no two-byte atomic compare and swap, so the __cmpxchg()
switch 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.

Signed-off-by: Bradley Morgan <brads@mainlining.org>
---
 arch/xtensa/include/asm/cmpxchg.h | 1 +
 1 file changed, 1 insertion(+)

Comments

Max Filippov Sept. 17, 2026, 1:32 a.m. UTC | #1 
On Wed, Sep 16, 2026 at 1:02 PM Bradley Morgan <brads@mainlining.org> wrote:
>
> Xtensa has no two-byte atomic compare and swap, so the __cmpxchg()
> switch 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.
>
> Signed-off-by: Bradley Morgan <brads@mainlining.org>
> ---
>  arch/xtensa/include/asm/cmpxchg.h | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
diff mbox series

Patch

diff --git a/arch/xtensa/include/asm/cmpxchg.h b/arch/xtensa/include/asm/cmpxchg.h
index b6db4838b175..8dea8e357fc0 100644
--- a/arch/xtensa/include/asm/cmpxchg.h
+++ b/arch/xtensa/include/asm/cmpxchg.h
@@ -76,6 +76,7 @@  __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
 {
 	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);
 	default: __cmpxchg_called_with_bad_pointer();
 		 return old;