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Re: [Qemu-devel] Re: playing with qemu usermode emulation on FreeBSD...


From: Blue Swirl
Subject: Re: [Qemu-devel] Re: playing with qemu usermode emulation on FreeBSD...
Date: Mon, 12 Oct 2009 22:55:24 +0300

On Mon, Oct 12, 2009 at 1:18 AM, Juergen Lock <address@hidden> wrote:
> On Thu, Oct 08, 2009 at 12:05:49AM +0200, Juergen Lock wrote:
>> I recently noticed there are x86 bsd-user targets now (yeah I totally
>> missed those commits...) and now got it working a tiny little bit:
>> I can run
>>       qemu-x86_64 -bsd freebsd /rescue/echo foo bar
>> here on FreeBSD 8/amd64 and it echoes foo bar as expected, but
>> segfaults afterwards. :)  (in pthread_setcancelstate() invoked from
>> a guest write() syscall, in case anyone is wondering.)  Other things
>> I tried either exit with errors or segfault as well, and i386 hosts
>> probably still don't work at all yet.  (qemu-i386 here on amd64 does
>> at least something, but probably needs lock_user() treatment for all
>> kinds of syscalls, I only tried adding that for sysctl so far.)
>>
>>  Anyway, here is an emulators/qemu-devel git head snapshot port
>> update with my current patches (files/patch-bsd-user), feel free to
>> test/debug/improve:
>>       http://people.freebsd.org/~nox/qemu/qemu-devel-20091007.patch
>> (For the folks reading this on the qemu list:  I shall start doing
>> `proper' patch submissions later, this is more for the FreeBSD folks
>> and because I was asked to send what I have...)
>
> New version at the same place, which now runs FreeBSD/{i386,sparc64}
> /rescue/echo on FreeBSD/amd64, the FreeBSD/amd64 target now segfaults
> in pthread_setcancelstate() invoked from the final writev() tho.
> Oh and I also uploaded the snapshot tarball so others can now actually
> build the port too... :)  And I have switched to the cpu-exec.c patch
> posted by Aleksej Saushev on the qemu list and added back amd64
> code there.
>
>  Here is the bsd-user patch again:

Please add Signed-off-by: line and use 'diff -u' (or preferably git diff).

> +    if (1 /* bsd_type == target_freebsd */)
> +        regs->rdi = infop->start_stack;

Why the if and comment?

> +        if (1 /* bsd_type == target_freebsd */) {
> +            regs->u_regs[8] = infop->start_stack;
> +            regs->u_regs[11] = infop->start_stack;

Same here.

>         case 0x100:
> +        /* FreeBSD uses 0x141 for syscalls too */
> +        case 0x141:
> +            if (bsd_type != target_freebsd)
> +                goto badtrap;

You are now also trapping on case 0x100 if bsd_type != target_freebsd,
which probably breaks other BSDs.

> +/* XXX this needs to be emulated on non-FreeBSD hosts... */
> +static abi_long do_freebsd_sysctl(abi_ulong namep, int32_t namelen, 
> abi_ulong oldp,
> +                          abi_ulong oldlenp, abi_ulong newp, abi_ulong 
> newlen)

What kind of call is this, is it possible to emulate on other BSDs? Is
it important? I'm just wondering if the cross-BSD emulation makes
sense after all. It would make the emulator much simpler if we could
assume that host_bsdness == target_bsdness.




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