On 01/07/16 17:10, Jan Beulich wrote:
>>>> On 01.07.16 at 17:38, <andrew.coop...@citrix.com> wrote:
>> As for interleaving inside the asm statement itself, we already have
>> precedent for that with the HAVE_GAS_* predicates. It would make the
>> patch rather larger, but might end up looking cleaner. It is probably
>> also worth switching to named parameters to reduce the risk of getting
>> positional parameters out of order.
> So taking just the first example I've converted: Do you think this
>
> static bool_t even_parity(uint8_t v)
> {
> asm ( "test %1,%1"
> #ifdef __GCC_ASM_FLAG_OUTPUTS__
> : "=@ccp" (v)
> #else
> "; setp %0"
> : "=qm" (v)
> #endif
> : "q" (v) );
>
> return v;
> }
>
> is better than the original?
How about a different example, from the second hunk
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 460d1f7..8d52a41 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -832,8 +832,19 @@ static int read_ulong(
static bool_t mul_dbl(unsigned long m[2])
{
bool_t rc;
- asm ( "mul %1; seto %2"
- : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
+
+ asm ( "mul %1;"
+#ifndef __GCC_ASM_FLAG_OUTPUTS__
+ "seto %[rc];"
+#endif
+ : "+a" (m[0]), "+d" (m[1]),
+#ifdef __GCC_ASM_FLAG_OUTPUTS__
+ [rc] "=@cco" (rc)
+#else
+ [rc] "=qm" (rc)
+#endif
+ );
+
return rc;
}
This at least doesn't mix the : inside an #ifdef
> I'm unsure, and I'm actually inclined to
> think that then the abstraction alternative might look better.
If the abstraction comes in two parts, one which may insert a `setcc`
instruction, and one which selects between =qm and =@cc, it wouldn't end
up hiding the :.
~Andrew
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