Re: [Xen-devel] [PATCH] xen/grant: Fix signed/unsigned comparisons issues

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 28/02/2020 08:41, Jan Beulich wrote:
> On 27.02.2020 19:46, Andrew Cooper wrote:
> > Each function takes an unsigned count, and loops based on a signed i.  This
> > causes problems when between 2 and 4 billion operations are requested.
> I can see problems, but not (as the title says) with comparison issues
> (the signed i gets converted to unsigned for the purpose of the
> comparison).
>
> > In practice, signed-ness issues aren't possible because count exceeding
> > INT_MAX is excluded earlier in do_grant_op(), but the code reads as if it is
> > buggy, and GCC obviously can't spot this either.
> >
> > Bloat-o-meter reports:
> >    add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-95 (-95)
> >    Function                                     old     new   delta
> >    do_grant_table_op                           7155    7140     -15
> >    gnttab_transfer                             2732    2716     -16
> >    gnttab_unmap_grant_ref                       771     739     -32
> >    gnttab_unmap_and_replace                     771     739     -32
> >    Total: Before=2996364, After=2996269, chg -0.00%
> >
> > and inspection of gnttab_unmap_grant_ref() at least reveals one fewer local
> > variables on the stack.
> This is a good thing for x86. However, having started to familiarize
> myself a tiny bit with RISC-V, I'm no longer certain our present way
> of preferring unsigned int for array indexing variable and alike is
> actually a good thing without further abstraction. Nevertheless, this
> isn't an immediate issue, so ...
Would you mind expanding a bit more about this comment here? How 
unsigned int is going to make things worse on RISC-V?
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel