Re: [PATCH v2 0/1] MR7231: rpcrt4: Change some buffer wrap checks to satisfy Clang 20.

[Jacek Caban (＠jacek)]

Jacek Caban (@jacek) commented about dlls/rpcrt4/ndr_marshall.c:
> - to do so */
>
> static inline void safe_copy_from_buffer(MIDL_STUB_MESSAGE *pStubMsg, void *p, ULONG size)
>  {
> - if ((pStubMsg->Buffer + size < pStubMsg->Buffer) || /* integer overflow of pStubMsg->Buffer */
> -
>    (pStubMsg->Buffer + size > pStubMsg->BufferEnd))
> - if (size > (SIZE_T)(pStubMsg->BufferEnd - pStubMsg->Buffer)) /* integer overflow of pStubMsg->Buffer */

The Clang warning comes from the fact that unsigned (and, by extension, pointer) overflow is undefined behavior in C, and this subtraction is technically the same situation.

I suppose we could first check that `BufferEnd` is not smaller than `Buffer` and then perform the comparison as you did, but without the `SIZE_T` cast.