Building with clang-cl

[gvanem]

When using clang-cl to compile the NPcap sources, there are some C++ errors that MSVC's compiler
does not even warn about even on -W4. Like this:

BOOLEAN PacketGetNetInfoEx(PCCH AdapterName, npf_if_addr* buffer, PLONG NEntries)
{
   ...
	if (!AdapterName || !buffer || NEntries <= 0) {   // !! here

Error:

./NPcap/packetWin7/Dll/Packet32.cpp(3220,42): error: ordered comparison between pointer and zero ('PLONG' (aka 'long *') and 'int')
        if (!AdapterName || !buffer || NEntries <= 0) {
                                       ~~~~~~~~ ^  ~

Surely it should be:

	if (!AdapterName || !buffer || *NEntries <= 0) {

A bug that surfaces depending on the raw location of *NEntries.

And then there are these errors:

./NPcap/packetWin7/Dll/Packet32.cpp(3672,8): error: case value evaluates to -1073676267, which cannot be narrowed to type 'DWORD'
      (aka 'unsigned long') [-Wc++11-narrowing]
                case NDIS_STATUS_INVALID_DATA:
                     ^
./NPcap/packetWin7/Dll/Packet32.cpp(3663,49): note: expanded from macro 'NDIS_STATUS_INVALID_DATA'
#define NDIS_STATUS_INVALID_DATA                ((NDIS_STATUS)0xC0010015L)
                                                ^
./NPcap/packetWin7/Dll/Packet32.cpp(3673,8): error: case value evaluates to -1073676265, which cannot be narrowed to type 'DWORD'
      (aka 'unsigned long') [-Wc++11-narrowing]
                case NDIS_STATUS_INVALID_OID:
                     ^
./NPcap/packetWin7/Dll/Packet32.cpp(3664,49): note: expanded from macro 'NDIS_STATUS_INVALID_OID'
#define NDIS_STATUS_INVALID_OID                 ((NDIS_STATUS)0xC0010017L)
                                                ^

Since NDIS_STATUS_INVALID_DATA == (NDIS_STATUS)0xC0010015L expands to (int) -1073676267 that's not suitable for a DWORD.
But with this patch, it compiles:

--- a/NPcap/packetWin7/Dll/Packet32.cpp 2022-08-20 12:20:53
+++ b/NPcap/packetWin7/Dll/Packet32.cpp 2022-08-20 08:27:46
@@ -3660,8 +3660,8 @@
        dwResult = PacketRequestHelper(hAdapter, TRUE, OidData);

 #ifndef NDIS_STATUS_INVALID_DATA
-#define NDIS_STATUS_INVALID_DATA                ((DWORD)0xC0010015UL)
-#define NDIS_STATUS_INVALID_OID                 ((DWORD)0xC0010017UL)
+#define NDIS_STATUS_INVALID_DATA                ((NDIS_STATUS)0xC0010015L)
+#define NDIS_STATUS_INVALID_OID                 ((NDIS_STATUS)0xC0010017L)
 #endif
        switch (dwResult)
        {

Or adding -Wno-c++11-narrowing.

I've not yet tried to use clang-cl for the driver code itself. I suspect more such issues there.

[dmiller-nmap]

This is a good catch on the NEntries issue. Most of the other things I see are C++-isms that would be good ideas, but would fit better under a complete rewrite to C++. I'm not entirely certain why the choice was made to move from C to C++ for Packet.dll, but the driver is still C. Clang does not seem to be able to understand the WDK headers, and so cannot actually build the driver, but it did find a few unused variables that I have now removed.

[gvanem]

Clang does not seem to be able to understand the WDK headers

Yes it does. I've built System Informer kernel with it.