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 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

See also

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.

 
cmd/cpuid.txt · Last modified: 2012/06/12 10:44 by mcb30
Recent changes RSS feed Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki
All uses of this content must include an attribution to the iPXE project and the URL http://ipxe.org
References to "iPXE" may not be altered or removed.