Re: [Xen-devel] [PATCH v5 4/4] xen/common: use SYMBOL when required

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 8 Jan 2019, Jan Beulich wrote:
> >>> On 07.01.19 at 20:16, <sstabellini@xxxxxxxxxx> wrote:
> > On Mon, 7 Jan 2019, Jan Beulich wrote:
> >> >>> On 03.01.19 at 20:19, <sstabellini@xxxxxxxxxx> wrote:
> >> > --- a/xen/common/virtual_region.c
> >> > +++ b/xen/common/virtual_region.c
> >> > @@ -119,7 +119,11 @@ void __init setup_virtual_regions(const struct 
> >> > exception_table_entry *start,
> >> >          const struct bug_frame *s;
> >> >  
> >> >          s = bug_frames[i - 1];
> >> > -        sz = bug_frames[i] - s;
> >> > +        /*
> >> > +         * Cast to unsigned long to calculate the size to avoid
> >> > +         * subtractions between pointers pointing to different objects.
> >> > +         */
> >> > +        sz = (unsigned long)bug_frames[i] - (unsigned long)s;
> >> 
> >> Perhaps better to use SYMBOL() in the definition of bug_frames[]?
> > 
> > That was my initial thought, but then bug_frames cannot be const and
> > cannot be statically initialized.
> 
> Oh, indeed. But there's no strong need for the "static", it just
> helps keeping code size small. Without it, none of ...
> 
> > So the code would become something like this:
> > 
> > void __init setup_virtual_regions(const struct exception_table_entry *start,
> >                                   const struct exception_table_entry *end)
> > {
> >     size_t sz;
> >     unsigned int i = 0;
> >     static unsigned long bug_frames[6];
> >     bug_frames[i++] = SYMBOL(__start_bug_frames);
> >     bug_frames[i++] = SYMBOL(__stop_bug_frames_0),
> >     bug_frames[i++] = SYMBOL(__stop_bug_frames_1),
> >     bug_frames[i++] = SYMBOL(__stop_bug_frames_2),
> > #ifdef CONFIG_X86
> >     bug_frames[i++] = SYMBOL(__stop_bug_frames_3),
> > #endif
> >     bug_frames[i++] = 0;
> 
> ... this really looks to be necessary.

Yes, you are right, that works. I'll do that.

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