The first argument is wrong. It needs to be the instruction number.

Nevermind. After reviewing some related source code from sys/x86/x86/identcpu.c first argument was correct:

1415         do_cpuid(1, regs);
1416         cpu_id = regs[0];
1417         cpu_procinfo = regs[1];
1418         cpu_feature = regs[3];
1419         cpu_feature2 = regs[2];
1420 #endif

Hmmm, does this show up elsewhere in the source base ? Seems like the fix could possibly go into sys/systm.h

This might need some error handling but that can wait for a future commit.

I left these without the (void) cast - there are some other instances like this in the file. Don't really mind either way. I'll talk to Leon about maybe some better error handling when the stream functions return an error.

Thanks - better solution than what I had (#ifndef bit_SSE42 then #define bit_SSE42)

Maybe. I do find it annoying how gcc 4.9 warns about this being unused... I'm not sure if it would compile out the check TBH, making it unusable.

Sounds good. This is dealing with -Wunused-but-set-variable warnings from gcc 4.8+.

This needs to be SSE42, not SSE41. Almost missed that typo.

I confirmed that this works and is correct:

 static int
-sse42_supported()
+sse42_supported(void)
 {
-       unsigned int eax, ebx, ecx, edx;
- 
-       __get_cpuid(1, &eax, &ebx, &ecx, &edx);
- 
-       return ((ecx & bit_SSE42) != 0);
+       u_int cpu_registers[4], ecx;
+
+       do_cpuid(1, cpu_registers);
+
+       ecx = cpu_registers[2];
+
+       return ((ecx & CPUID2_SSE42) != 0);
 }
 
 int