Re: [libvirt] [PATCH 4/4] virFree: Check const correctness

On Tue, Jul 15, 2014 at 02:38:36PM +0200, Michal Privoznik wrote: > Up to now it's possible to do something like this: > > const char *ptr; > > ptr = strdup("my example string"); > > VIR_FREE(ptr); > > The problem is, const char * pointers should not be modified (and > freeing them is kind of modification). We should avoid this. A little > trick is used: assigning a const pointer into 'void *' triggers > compiler warning about discarding 'const' qualifier from pointer. So > the virFree() function gains new dummy argument, that is not touched > anyhow, just fulfills the const correctness check duty. > > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > --- > src/util/viralloc.c | 6 ++++-- > src/util/viralloc.h | 20 ++++++++++++++++---- > src/xenapi/xenapi_utils.c | 2 +- > 3 files changed, 21 insertions(+), 7 deletions(-) > > diff --git a/src/util/viralloc.c b/src/util/viralloc.c > index be9f0fe..0134e67 100644 > --- a/src/util/viralloc.c > +++ b/src/util/viralloc.c [...] > @@ -569,13 +569,15 @@ int virAllocVar(void *ptrptr, > > /** > * virFree: > + * @ptr: dummy pointer to check const correctness > * @ptrptr: pointer to pointer for address of memory to be freed > * > * Release the chunk of memory in the pointer pointed to by > * the 'ptrptr' variable. After release, 'ptrptr' will be > * updated to point to NULL. > */ > -void virFree(void *ptrptr) > +void virFree(void *ptr ATTRIBUTE_UNUSED, > + void *ptrptr) What if you don't add another argument, but just change the void *ptrptr to void **ptrptr. Compiler shouldn't be mad about not knowing the size resulting of de-referencing ptrptr, you get the check you want and keep the macro without side-effects.