[cfe-dev] Clang doesn't warn about wrong sized mallocs

Ben Boeckel via cfe-dev cfe-dev at lists.llvm.org
Tue Aug 17 04:20:24 PDT 2021

On Mon, Aug 16, 2021 at 19:03:04 +0200, Joerg Sonnenberger via cfe-dev wrote:
> On Mon, Aug 16, 2021 at 03:48:54PM +0000, Keane, Erich via cfe-dev wrote:
> > I think the only valid thing to check here is allocated 'smaller', since:
> > 
> > struct S *s = malloc(sizeof(struct S) * 10); // An array
> > struct S *s2 = malloc(sizeof(struct S) + 5); // a struct with some level of trailing storage, shows that multiple-of isn't sufficient
> > 
> > are both valid/reasonably common uses of malloc.
> It depends. The former is certainly valid and common, but the latter
> should only be valid if the last member is a (flexible) array. There are
> certainly levels of quality here.

Isn't `malloc(sizeof(S) + sizeof(T))` (plus any required padding for the
alignment of `T`) how `std::make_shared` works to allocate the
accounting block right beside the object though? That seems valid to me.


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