CMake fails on Windows when building ARM64 on x64 host

[dmiller-nmap]

The SUITABLE_SNPRINTF check fails because the resulting ARM64 code cannot be run on the x64 host. CMAKE_CROSSCOMPILING is not set because both systems have the same CMAKE_SYSTEM_NAME ("Windows"). Not sure the best way to handle this, since a general check for identical architectures would miss the cases of ARM64 and x64 host systems targeting x86.

libpcap/CMakeLists.txt

Lines 738 to 792 in 3bb233f

	if (NOT CMAKE_CROSSCOMPILING)
	#
	# Require a proof of suitable snprintf(3), same as in Autoconf.
	#
	include(CheckCSourceRuns)
	check_c_source_runs("
	#include <stdio.h>
	#include <string.h>
	#include <inttypes.h>
	#include <sys/types.h>
	int main()
	{
	char buf[100];
	uint64_t t = (uint64_t)1 << 32;
	snprintf(buf, sizeof(buf), \"%zu\", sizeof(buf));
	if (strncmp(buf, \"100\", sizeof(buf)))
	return 1;
	snprintf(buf, sizeof(buf), \"%zd\", -sizeof(buf));
	if (strncmp(buf, \"-100\", sizeof(buf)))
	return 2;
	snprintf(buf, sizeof(buf), \"%\" PRId64, -t);
	if (strncmp(buf, \"-4294967296\", sizeof(buf)))
	return 3;
	snprintf(buf, sizeof(buf), \"0o%\" PRIo64, t);
	if (strncmp(buf, \"0o40000000000\", sizeof(buf)))
	return 4;
	snprintf(buf, sizeof(buf), \"0x%\" PRIx64, t);
	if (strncmp(buf, \"0x100000000\", sizeof(buf)))
	return 5;
	snprintf(buf, sizeof(buf), \"%\" PRIu64, t);
	if (strncmp(buf, \"4294967296\", sizeof(buf)))
	return 6;
	return 0;
	}
	"
	SUITABLE_SNPRINTF
	)
	if(NOT SUITABLE_SNPRINTF)
	message(FATAL_ERROR
	"The snprintf(3) implementation in this libc is not suitable,
	libpcap would not work correctly even if it managed to compile."
	)
	endif()
	else()
	message(STATUS "Skipped SUITABLE_SNPRINTF because cross-compiling.")
	endif()

[infrastation]

Could you add the steps to reproduce the problem?

[mcr]

I don't think we've ever supported cross-compiling on Windows.

But, it seems that "Windows" as a value for CMAKE_SYSTEM_NAME is wrong, if it implies x86_64, and Windows now supports building for ARM. Maybe WSL + ./configure is a better route.

[dmiller-nmap]

The CMake command I ran is in a script in Npcap's source tree. I believe the crucial part is the -A ARM64, but here is the entire command as run:

%CMAKE% -A ARM64 -DCMAKE_DISABLE_FIND_PACKAGE_OpenSSL=TRUE -DOpenSSL_FOUND=FALSE -DCMAKE_C_FLAGS_INIT="/guard:cf" -DCMAKE_SHARED_LINKER_FLAGS_INIT="/guard:cf" -DPacket_ROOT=..\%NPCAP_SDK% -DLIBRARY_NAME=wpcap -G "Visual Studio 17 2022" ..\libpcap\

[guyharris]

I believe the crucial part is the -A ARM64

According to the CMake 3.12 "cmake" command documentation (3.12 being the minimum version of CMake we require on Windows), -A "[Specifies] platform name if supported by generator." Following various links, it appears that this affects the value of the CMAKE_VS_PLATFORM_NAME variable.

Unfortunately, as you noted, CMAKE_CROSSCOMPILING is defined to mean "compiling for a different operating system", not "compiling for a different instruction set"; good luck if you're compiling for an Arm embedded Linux system on an x86 Linux system.

It appears that "cross-compiling for a different instruction set" amounts to CMAKE_SYSTEM_PROCESSOR not being equal to CMAKE_HOST_SYSTEM_PROCESSOR.

[guyharris]

See if this fixes it. (The check for a cross-compile doesn't occur in the 1.10 branch, so this doesn't need to be backported; we're not doing a check for a working snprintf() there.)

[dmiller-nmap]

It's working for me now, thanks.