[Xen-devel] [PATCH 3/5] x86/hvm: Adjust hvmemul_rep_stos() to compile with -Wvla

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

For at least "gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609", the
typecast of buf triggers a Variable Length Array warning.

Alter the asm expression to avoid the typecast, which necessitates the
introduction of a memory clobber as the compiler can no longer identify
the total quantity of written memory.

Despite the memory clobber, there is no change to the generated.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 xen/arch/x86/hvm/emulate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index a577685..eab66ea 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -1859,7 +1859,7 @@ static int hvmemul_rep_stos(
     switch ( p2mt )
     {
         unsigned long bytes;
-        void *buf;
+        char *buf;
 
     default:
         /* Allocate temporary buffer. */
@@ -1882,10 +1882,10 @@ static int hvmemul_rep_stos(
 #define CASE(bits, suffix)                                     \
             case (bits) / 8:                                   \
                 asm ( "rep stos" #suffix                       \
-                      : "=m" (*(char (*)[bytes])buf),          \
+                      : "=m" (*buf),                           \
                         "=D" (dummy), "=c" (dummy)             \
                       : "a" (*(const uint##bits##_t *)p_data), \
-                         "1" (buf), "2" (*reps) );             \
+                        "1" (buf), "2" (*reps) : "memory" );   \
                 break
             CASE(8, b);
             CASE(16, w);
-- 
2.1.4


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