Re: [Xen-devel] [PATCH v11 9/9] xen: explicit casts when DECLARE_BOUNDS cannot be used

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.03.19 at 23:38, <sstabellini@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -976,7 +976,8 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>           * respective reserve_e820_ram() invocation below.
>           */
>          mod[mbi->mods_count].mod_start = virt_to_mfn(_stext);
> -        mod[mbi->mods_count].mod_end = __2M_rwdata_end - _stext;
> +        mod[mbi->mods_count].mod_end = (uintptr_t)__2M_rwdata_end -
> +                                       (uintptr_t) _stext;

Did you consider changing __2M_rwdata_end's declaration and using
text_bytediff() here? Otherwise, if the casts are to stay, the stray
blank after the second one should go away.

> --- a/xen/common/virtual_region.c
> +++ b/xen/common/virtual_region.c
> @@ -119,7 +119,9 @@ 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;
> +        /* bug_frame[i] and s are pointers to different objects. */
> +        sz = ((uintptr_t)bug_frames[i] - (uintptr_t)s) /
> +             sizeof(struct bug_frame);

I disagree with the comment, and if you think it is correct, then no
matter what you do the behavior is undefined. Instead I view the
entirety of the .bug_frames.* sections as a single array, with
labels placed not only at start and end, but also in the middle. I
think the code here would better also be taken care of by the
DECLARE_BOUNDS() machinery, dividing the single array into
multiple smaller ones.

Jan



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