Re: [patch 12/17] Consistently wrap paravirt ops callsites to make them patchable

Andi Kleen
2007-04-02T07:12:57Z

On Monday 02 April 2007 07:57, Jeremy Fitzhardinge wrote:
> Wrap a set of interesting paravirt_ops calls in a wrapper which makes
> the callsites available for patching. Unfortunately this is pretty
> ugly because there's no way to get gcc to generate a function call,
> but also wrap just the callsite itself with the necessary labels.
>
> This patch supports functions with 0-4 arguments, and either void or
> returning a value. 64-bit arguments must be split into a pair of
> 32-bit arguments (lower word first). Small structures are returned in
> registers.

Can you please add some comments to the code explaining this a little?
Best would be perhaps a overview document in Documentation too.

> +#define PVOP_CALL0(__rettype, __op) \

The __s shouldn't be needed for the macro arguments because
there is no shared name space with the caller.

> + ({ \
> + __rettype __ret; \
> + if (sizeof(__rettype) > sizeof(unsigned long)) { \
> + unsigned long long __tmp; \
> + unsigned long __ecx; \
> + asm volatile(paravirt_alt(PARAVIRT_CALL) \

Not having the volatile would probably generate better code, but it
seems much safer for now.

> + : "=A" (__tmp), "=c" (__ecx) \
> + : paravirt_type(__op), \
> + paravirt_clobber(CLBR_ANY) \
> + : "memory", "cc"); \

And the cc clobber is also not needed

-Andi