This is an old revision of the document!

Check x86 CPU feature

Synopsis

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

Examples

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

  cpuid --amd 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 --amd --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 --amd option is specified then the AMD-defined ("extended") feature set is checked, otherwise the Intel-defined ("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
AMD	`%edx`	29	Long mode (64-bit)	`cpuid --amd 29`
Intel	`%edx`	6	Physical address extensions (PAE)	`cpuid 6`
Intel	`%ecx`	5	Virtual Machine Extensions (VMX)	`cpuid --ecx 5`
AMD	`%ecx`	2	Secure Virtual Machine (SVM)	`cpuid --amd --ecx 2`
Intel	`%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 Intel-defined ("standard") feature set represents the values returned in %ecx and %edx when CPUID is called with %eax=0x00000001.

The AMD-defined ("extended") feature set represents the values returned in %ecx and %edx when CPUID is called with %eax=0x80000001.

Table of Contents