Re: [Xen-devel] [PATCH v2 for-4.10] ubsan: add clang 5.0 support

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Oct 18, 2017 at 03:53:37AM -0600, Jan Beulich wrote:
> >>> On 18.10.17 at 11:42, <roger.pau@xxxxxxxxxx> wrote:
> > On Wed, Oct 18, 2017 at 03:23:20AM -0600, Jan Beulich wrote:
> >> >>> On 18.10.17 at 09:45, <roger.pau@xxxxxxxxxx> wrote:
> >> > +void __ubsan_handle_pointer_overflow(struct pointer_overflow_data *data,
> >> > +                                unsigned long base, unsigned long 
> >> > result)
> >> > +{
> >> > +        unsigned long flags;
> >> > +
> >> > +        if (suppress_report(&data->location))
> >> > +                return;
> >> > +
> >> > +        ubsan_prologue(&data->location, &flags);
> >> > +
> >> > +        if (((long)base >= 0) == ((long)result >= 0))
> >> > +                pr_err("pointer operation %s %p to %p\n",
> >> > +                        base > result ? "underflowed" : "overflowed",
> >> > +                        (void *)base, (void *)result);
> >> > +        else
> >> > +                pr_err("pointer index expression with base %p 
> >> > overflowed to %p\n",
> >> > +                        (void *)base, (void *)result);
> >> 
> >> Would you mind explaining the difference between if and else
> >> branches? (I do realize I should have asked this on v1 already,
> >> but I didn't pay enough attention.) Whatever the idea behind
> >> this, it should probably be explained in a comment, as it looks
> >> to be heuristic.
> > 
> > The upstream commit is:
> > 
> > https://github.com/llvm-mirror/compiler-rt/commit/079b7657767dcc0fb284225c277d
> >  
> > 2b9ce73e423b
> > 
> > However it's lacking a proper commit message. It seems to me like it's
> > there to detect addition of signed + unsigned values when an overflow
> > happens, but I don't really see it's value rather than just using the
> > first message.
> 
> Right - me too. I'd therefore like to simply drop the "if" and the "else"
> branch (likely easily done while committing), and then the change is
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Yes, feel free to drop the if/else and just keep the first error
message.

Thanks, Roger.

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