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Re: [PATCH 2/2] x86/alternatives: adjust alternative_vcall0()

To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>

Date: Thu, 18 Nov 2021 15:06:53 +0800

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Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>

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On 2021/11/17 16:00, Jan Beulich wrote:

I'm puzzled about two inconsistencies with other alternative_vcall<N>()
here: There's a check missing that the supplied function pointer is
actually pointing to a function taking no args. And there's a pointless
pair of parentheses. Correct both.

Fixes: 67d01cdb5518 ("x86: infrastructure to allow converting certain indirect calls 
to direct ones")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -218,7 +218,8 @@ extern void alternative_branches(void);

#define alternative_vcall0(func) ({ \

      ALT_CALL_NO_ARG1;                           \
-    ((void)alternative_callN(0, int, func));    \
+    (void)sizeof(func());                       \
+    (void)alternative_callN(0, int, func);      \
  })

#define alternative_call0(func) ({ \

Reviewed-by: Wei Chen <Wei.Chen@xxxxxxx>

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