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On 01/07/16 17:10, Jan Beulich wrote:
On 01.07.16 at 17:38, <andrew.cooper3@xxxxxxxxxx> 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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