Re: [Qemu-devel] How does a system call work on QEMU?

[Mulyadi Santosa <mulyadi.santosa@gmail.com>]

On Thu, May 14, 2009 at 1:50 PM,  <helicoterus-elih@yahoo.it> wrote:
>
>
>> Which mode of Qemu operations do you refer to? if you refer to full
>> MMU emulation (no KVM or kqemu involved then), then intercepting
>> syscall is basically intercepting interrupt 80 hex or SYSENTER/SYSCALL
>> into host user mode instruction during code translation.
>
> Ok, I refer to full emulation.
> When QEMU intercepts a system call what does it do? What type of translation or modification does it perform?

OK then, just like Paul said, it's done exactly like normal hardware
does. Emulated APIC will intercept it and Qemu will jump executing the
handler.

IMHO, translation is done when Qemu executes the guest codes, be it in
user mode or kernel mode. Refer to Fabrice's paper on how translation
is done (mind you, it's using pre TCG method). On special case, where
qemu emulates the same type of machine (e.g x86 32 bit on x86 32 bit),
AFAIK Qemu does few code copy tricks, so no all codes must be
translated.

More knowledgeable people in this mailing list could give you better
explanation... so pardon me if I can not answer all of your doubt.

regards,

Mulyadi