Re: [Xen-devel] [PATCH] i386 linux: make 32-bit PAE kernel work when built with newer gcc

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 14 Mar 2006, at 12:40, Jan Beulich wrote:

> I'm not sure this is correct - the standard, in section 5.1.2.3, says
>
> "Accessing a volatile object, modifying an object, modifying a file, 
> or calling a function
> that does any of those operations are all side effects, which are 
> changes in the state of
> the execution environment. Evaluation of an expression may produce 
> side effects. At
> certain specified points in the execution sequence called sequence 
> points, all side effects
> of previous evaluations shall be complete and no side effects of 
> subsequent evaluations
> shall have taken place."
>
> As we're talking about modifying an object, this being considered a 
> side-effect means it
> must have been carried out by the time the ; is (logically) reached.
See 5.1.2.3.5 and then the examples 5.1.2.3.8 and 5.1.2.3.9 
(particularly the first sentence, which summarises the guarantee 
provided by an aggressive optimising C compiler).
The standard is really not clear in this respect, but I take 5.1.2.3.2 
to apply to the abstract machine, and not necessarily an 
implementation. But I am not a compiler writer. :-)
 -- Keir


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