;name: cpuid
;
;build: nasm -felf64 cpuid.asm -o cpuid.o
; ld -s -melf_x86_64 -o cpuid cpuid.o
;
;description: Checks if CPUID instruction is supported and if yes, shows also the Vendor ID
[list -]
%include "unistd.inc"
%include "cpu/cpu.inc"
[list +]
section .data
output: db "The processor Vendor ID is '"
.regEBXvalue: db "xxxx"
.regEDXvalue: db "xxxx"
.regECXvalue: db "xxxx"
db "'", 10
.len: equ $-output
nosupport: db "CPUID is not supported", 10
.len: equ $-nosupport
section .text
global _start
_start:
;assemble in 32 bit mode
bits 32
;returns 1 if CPUID is supported, 0 otherwise (ZF is also set accordingly)
pushfd ;get 32 bits flags
pop eax ;and put in EAX
mov ecx,eax ;save the original flags state in ECX
xor eax,0x200000 ;flip bit 21
push eax ;and put via EAX
popfd ;on stack
pushfd ;get the flags again
pop eax ;put in EAX
xor eax,ecx ;and check if bit 21 is the same as stored before
shr eax,21 ;move bit 21 to bit 0
and eax,1 ;and mask others
push ecx ;
popfd ;and restore original flags
jnz .supported
bits 64
syscall write,stdout,nosupport,nosupport.len
syscall exit
.supported:
; CPUID is supported
xor eax,eax ;get vendor ID
cpuid
mov [output.regEBXvalue],ebx ;first 4 letters of vendor from ebx in place
mov [output.regEDXvalue],edx ;next 4 letters of vendor from edx in place
mov [output.regECXvalue],ecx ;last 4 letters of vendor from ecx in place
syscall write,stdout,output,output.len
syscall exit
