Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

H. Peter Anvin
2010-07-14T17:46:13Z

On 07/14/2010 10:34 AM, Jeremy Fitzhardinge wrote:
> On 07/14/2010 10:30 AM, H. Peter Anvin wrote:
>> If gcc ever starts reordering volatile operations, including "asm
>> volatile", the kernel will break, and will be unfixable. Just about
>> every single driver will break. All over the kernel we're explicitly or
>> implicitly making the assumption that volatile operations are strictly
>> ordered by the compiler with respect to each other.
>
> Can you give an example? All the cases I've seen rely on the ordering
> properties of "memory" clobbers, which is sound. (And volatile
> variables are a completely unrelated issue, of course.)
>

I/O ports, for example.

-hpa