Division by zero on TSC calculation when running on Virtualbox 6

[alex-ab]

Thanks for your nice tool! Much enjoyed it during our AVX enablement of Vbox6 on our OS.

During testing it on our port and also on a vanilla Linux VM (Debian) on a Linux (Ubuntu 22.04) + Virtualbox6 host, a division by zero happens. It seems Virtualbox 6 does not provide all the expected CPUID values you need. The following patch avoids the issue and instead the TSC frequency is measured and avx-turbo works afterwards.

--- a/tsc-support.cpp
+++ b/tsc-support.cpp
@@ -41,7 +41,7 @@ uint64_t get_tsc_from_cpuid_inner() {
 
 
     if (family.family == 6) {
-        if (family.model == 0x4E || family.model == 0x5E || family.model == 0x8E || family.model == 0x9E) {
+        if (cpuid15.eax && (family.model == 0x4E || family.model == 0x5E || family.model == 0x8E || family.model == 0x9E)) {
             // skylake client or kabylake
             return (int64_t)24000000 * cpuid15.ebx / cpuid15.eax; // 24 MHz crystal clock
         }