Re: [PATCH] ubsan: improve bounds checking, add -fsanitize=bounds-strict

[Marek Polacek <polacek@redhat.com>]

On Fri, Feb 27, 2015 at 11:53:14AM -0800, Martin Uecker wrote:
> 
> I tested Marek's proposed change and it works correctly,
> i.e. arrays which are not part of a struct are now
> instrumented when accessed through a pointer. This also
> means that the following case is diagnosed (correctly)
> as undefined behaviour as pointed out by Richard:
> 
> int
> main (void)
> {
>   int *t = (int *) __builtin_malloc (sizeof (int) * 9);
>   int (*a)[3][3] = (int (*)[3][3])t;
>   (*a)[0][9] = 1;
> }
> 
> 
> I also wanted arrays which are the last elements of a
> struct which are not flexible-array members instrumented 
> correctly. So I added -fsantitize=bounds-strict which does
> this. It seems to do instrumentation similar to clang 
> with -fsanitize=bounds.
> 
> Comments?
 
Thanks for working on it.  So I think we should split this patch in
two; one part is a bug fix (I've opened
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65280>) that could go
into gcc 5 - that is, apply my fix along with test cases covering the
new cases, and the second part is an addition of a new option for
strict bounds checking - I'm afraid this part has to wait for gcc 6.

I can take care of the first part and let you do the second part, which I
could review.  Does that sound ok to you?

Jeff, would you agree with this approach?  The fix is sort of obvious
and my understanding is that Jakub's ok with it too.

	Marek