[PATCH] Check for null pointers in ubsan

[Alexey Samsonov]

+Richard

C99 (and C11) standards suggests passing NULL to memcpy is an undefined
behavior:

7.21.1.2 (String function conventions): Unless explicitly stated otherwise
in the description of a particular function
in this subclause, pointer arguments on such a call shall still have valid
values, as described in 7.1.4.

7.1.4.1 If an argument to a function has an invalid value (such as a <...>
null pointer <...>) <...> the behavior is undefined.

I'm not sure if it's overriden by POSIX/Linux, though, and if GCC has full
right to optimize on this.

On Mon, May 11, 2015 at 2:40 PM, Nuno Lopes <nunoplopes at sapo.pt> wrote:

> On Mon, May 11, 2015 at 07:00:53PM +0000, Nuno Lopes wrote:
>>
>>> gcc 4.9 just got more aggressive and is now exploiting the fact that
>>> input pointers to memcpy/memmove cannot be null (even if the size is 0).
>>>
>>
>> Are you sure that this is GCC and not glibc? Can someone *please* raise
>> a defect report against the C standard? This is ridiculous...
>>
>
> I had to debug a big project over this weekend because it was being
> miscompiled with gcc 4.9.
> Apparently the porting guide (https://gcc.gnu.org/gcc-4.9/porting_to.html)
> states that gcc is now more aggressive in optimizing away null pointer
> checks.
>
> Nuno
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>



-- 
Alexey Samsonov
vonosmas at gmail.com
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