This is xnu-8019. See this file in:
#include <darwintest.h>
#include <sys/sysctl.h>

T_DECL(sysctl_hw_cpu, "ensure vital product and CPU-related sysctls exist")
{
	char buffer[64] = "";
	size_t buffer_size = sizeof(buffer);
	int v;
	size_t v_size;

	int ret = sysctlbyname("hw.target", buffer,
	    &buffer_size, NULL, 0);
	T_ASSERT_POSIX_SUCCESS(ret, "hw.target sysctl");
	T_LOG("hw.target = %s", buffer);

	buffer_size = sizeof(buffer);

	ret = sysctlbyname("hw.product", buffer,
	    &buffer_size, NULL, 0);
	T_ASSERT_POSIX_SUCCESS(ret, "hw.product sysctl");
	T_LOG("hw.product = %s", buffer);

	buffer_size = sizeof(buffer);

	ret = sysctlbyname("machdep.cpu.brand_string", buffer,
	    &buffer_size, NULL, 0);

	T_ASSERT_POSIX_SUCCESS(ret, "machdep.cpu.brand_string sysctl");
	T_LOG("machdep.cpu.brand_string = %s", buffer);

	v = 0;
	v_size = sizeof(v);
	ret = sysctlbyname("hw.cpu64bit_capable", &v, &v_size, NULL, 0);
	T_ASSERT_POSIX_SUCCESS(ret, "hw.cpu64bit_capable");

#if __arm__
	T_EXPECT_EQ(v, 0, "cpu is not 64 bit capable");
#else
	T_EXPECT_EQ(v, 1, "cpu is 64 bit capable");
#endif
}