Virtual 8086 Mode: Difference between revisions

EFLAGS.VM is NEVER pushed onto the stack if the V86 task uses PUSHFD. You should check if CR0.PE=1 and then assume it's V86 if that bit is set.

 

detect_v86:

smsw ax

and eax,1 ;CR0.PE bit

ret

 

VM mode detection is mainly useful when writing DOS extenders or other programs that could be started either in plain real mode or in virtual mode from a protected mode system. An 'ordinary' bootloader shouldn't worry about this since the BIOS will not set up VM86 to read the bootsector ;)