[cfe-commits] [PATCH 1/1] Checking zero byte allocation for realloc() and calloc().

[Jordy Rose]

I didn't look into the patch in detail, but it's worth noting that realloc can be safe with a 0 size on BSD, at least. ("If size is zero and ptr is not NULL, a new, minimum sized object is allocated and the original object is freed." but "If ptr is NULL, realloc() is identical to a call to malloc() for size bytes.")

Also, how much overlap is there with MallocChecker? There's a fixme on CheckMallocZero already about having malloc-related checks in two places.

Still, sounds like a good add. Thanks for working on this!

Jordy


On Nov 13, 2011, at 8:52, Cyril Roelandt wrote:

> Hello,
> 
> Currently, clang can check zero byte allocations for the malloc function. I think it should also warn programmers about zero byte allocations for the calloc and realloc functions.
> 
> Attached is a patch that implements this idea. It checks either the first argument of malloc(), or the second argument of realloc(), or both arguments of calloc(), looking for a value constrained to 0.
> 
> Checking both arguments of calloc() makes the code a little bit ugly, so I'll probably need to give it some more work.
> 
> You may find a test case attached to this mail :
> 
> $ clang --analyze -c -o alloc alloc.c
> /tmp/alloc.c:29:16: warning: Call to 'malloc' has an allocation size of 0 bytes
>   int *ptr = malloc(0);
>              ^      ~
> /tmp/alloc.c:36:16: warning: Call to 'calloc' has an allocation size of 0 bytes
>   int *ptr = calloc(0, sizeof(int));
>              ^      ~
> /tmp/alloc.c:43:16: warning: Call to 'calloc' has an allocation size of 0 bytes
>   int *ptr = calloc(42, 0);
>              ^          ~
> /tmp/alloc.c:50:16: warning: Call to 'realloc' has an allocation size of 0 bytes
>   int *ptr = realloc(NULL, 0);
>              ^             ~
> 
> Looking forward to hearing from you,
> Cyril Roelandt.
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