In cases like this, I always wonder WWPD (What Would Pinski Do)...
Let's get him to opine.
Andrew, the patch in question is:
http://www.linux-mips.org/archives/linux-mips/2014-05/msg00309.html
Thanks,
David Daney
On 06/03/2014 08:03 AM, Andreas Herrmann wrote:
On Tue, Jun 03, 2014 at 10:30:31AM +0200, Ralf Baechle wrote:
On Wed, May 28, 2014 at 11:52:12PM +0200, Andreas Herrmann wrote:
+/*
+ * Hypercalls for KVM.
+ *
+ * Hypercall number is passed in v0.
+ * Return value will be placed in v0.
+ * Up to 3 arguments are passed in a0, a1, and a2.
+ */
+static inline unsigned long kvm_hypercall0(unsigned long num)
+{
+ register unsigned long n asm("v0");
+ register unsigned long r asm("v0");
Btw, is it safe to put two variables in the same register?
I think it's safe.
If we would have a matching constraint letter (say "v" for register v0) the
asm should translate to
__asm__ __volatile__(
KVM_HYPERCALL
: "=v" (n) : "v" (r) : "memory"
);
which isn't unusual on other archs. (Or maybe I am just biased from
x86 ... or missed something else.)
The syscall wrappers that used to be in <asm/unistd.h> were occasionally
hitting problems which eventually forced me to stop forcing variables
into particular registers instead using a MOVE instruction to shove
each variable into the right place.
Of course they were being used from non-PIC and PIC code, kernel and userland
so GCC had a much better chance to do evil than in the hypercall wrapper
case - but it made me paranoid ...
Andreas
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
