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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan



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