Check x86 CPU feature

Synopsis

  cpuid [--ext] [--ecx] <bit number>

Examples

Check if CPU supports 64-bit operation ("long mode")

  cpuid --ext 29 && set arch x86_64 || set arch i386

Check if CPU supports physical address extensions ("PAE")

  cpuid 6 && set pae yes ||

Check if CPU supports hardware virtualisation

  cpuid --ecx 5 && set vmx yes ||
  cpuid --ext --ecx 2 && set svm yes ||
  isset ${vmx} || isset ${svm} && set hw_virt yes ||

Description

Check for the existence of the specified x86 CPU feature using the CPUID instruction. If the --ext option is specified then the extended feature set is checked, otherwise the standard feature set is checked. If the --ecx option is specified then the feature set contained in the %ecx register is checked, otherwise the feature set contained in the %edx register is checked.

Some useful features to check are:

Feature set	Register	Bit	Feature	Command
Extended	`%edx`	29	Long mode (64-bit)	`cpuid --ext 29`
Standard	`%edx`	28	Hyper-threading (HTT)	`cpuid 28`
Standard	`%edx`	6	Physical address extensions (PAE)	`cpuid 6`
Standard	`%ecx`	5	Intel Virtual Machine Extensions (VMX)	`cpuid --ecx 5`
Extended	`%ecx`	2	AMD Secure Virtual Machine (SVM)	`cpuid --ext --ecx 2`
Standard	`%edx`	15	Conditional Move (CMOV)	`cpuid 15`

Command status

Success	The specified x86 CPU feature is present
Failure	The specified x86 CPU feature is not present

Notes

The standard feature set represents the values returned in %ecx and %edx when CPUID is called with %eax=0x00000001.

The extended feature set represents the values returned in %ecx and %edx when CPUID is called with %eax=0x80000001.

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