Re: Bug with Windows tap network when running qemu-system-ppc with Mac OS 9 guest

[Howard Spoelstra]

On Fri, Mar 26, 2021 at 8:54 PM BALATON Zoltan <balaton@eik.bme.hu> wrote:
>
> On Fri, 26 Mar 2021, Howard Spoelstra wrote:
> > On Fri, Mar 26, 2021 at 10:00 AM Bin Meng <bmeng.cn@gmail.com> wrote:
> >>
> >> On Fri, Mar 26, 2021 at 4:49 PM Jason Wang <jasowang@redhat.com> wrote:
> >>>
> >>>
> >>> 在 2021/3/26 下午4:21, BALATON Zoltan 写道:
> >>>> On Fri, 26 Mar 2021, Howard Spoelstra wrote:
> >>>>> On Fri, Mar 26, 2021 at 2:50 AM Bin Meng <bmeng.cn@gmail.com> wrote:
> >>>>>>
> >>>>>> Hi Howard,
> >>>>>>
> >>>>>> On Fri, Mar 26, 2021 at 1:35 AM Peter Maydell
> >>>>>> <peter.maydell@linaro.org> wrote:
> >>>>>>>
> >>>>>>> (adding the relevant people to the cc list)
> >>>>>>>
> >>>>>>> On Thu, 25 Mar 2021 at 17:26, Howard Spoelstra <hsp.cat7@gmail.com>
> >>>>>>> wrote:
> >>>>>>>>
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>> When running qemu-system-ppc with Mac OS guest, the guest crashes
> >>>>>>>> when
> >>>>>>>> using a tap network connection. Openvpn 2.4.9-I601-win10 is installed
> >>>>>>>> with TAP-Windows 9.24.2. A tap connection called TapQemu is bridged
> >>>>>>>> with the default ethernet connection. It gets activated when I start
> >>>>>>>> qemu.
> >>>>>>>>
> >>>>>>>> To reproduce, compile qemu-system-ppc from current source and run:
> >>>>>>>>
> >>>>>>>> qemu-system-ppc.exe ^
> >>>>>>>> -L pc-bios ^
> >>>>>>>> -M mac99 ^
> >>>>>>>> -m 128 ^
> >>>>>>>> -sdl -serial stdio ^
> >>>>>>>> -boot c ^
> >>>>>>>> -drive file=C:\Mac-disks\9.2.img,format=raw,media=disk ^
> >>>>>>>> -device sungem,netdev=network01 -netdev
> >>>>>>>> tap,ifname=TapQemu,id=network01
> >>>>>>>>
> >>>>>>>> I bisected to the commit below. Thanks for looking into this.
> >>>>>>
> >>>>>> Thanks for reporting.
> >>>>>>
> >>>>>> Can you please provide some further information:
> >>>>>>
> >>>>>> 1. Does "-net user" work on Windows?
> >>>>>> 2. If running QEMU under Linux, does "-net tap" or "-net user" work?
> >>>>>>
> >>>>>> Regards,
> >>>>>> Bin
> >>>>>
> >>>>> Hello Bin,
> >>>>>
> >>>>> Thanks for getting back to me. I forgot to mention that reverting the
> >>>>> above patch restores functionality. And that other applications using
> >>>>> the same tap device work correctly.
> >>>>> In answer to your questions:
> >>>>>
> >>>>> 1. Yes, slirp works on Windows 10 with this setup.
> >>>>> 2. Yes, in Linux both tap and slirp work.
> >>>>>
> >>>>> My Windows build is done with a fully up to date msys2 installation.
> >>>>>
> >>>>> I tried to debug in Windows:
> >>>>> (gdb) run
> >>>>> Starting program: c:\qemu-master-msys2\qemu-system-ppc.exe -L pc-bios
> >>>>> -M mac99 -m 128 -sdl -serial stdio -boot c -drive
> >>>>> "file=C:\Mac-disks\9.2-usb-pci-ddk.img,format=raw,media=disk" -device
> >>>>> "sungem,netdev=network01" -netdev "tap,ifname=TapQemu,id=network01" -S
> >>>>> [New Thread 13304.0x1f00]
> >>>>> [New Thread 13304.0x2f84]
> >>>>> [New Thread 13304.0x3524]
> >>>>> [New Thread 13304.0x2b8c]
> >>>>> [New Thread 13304.0x368c]
> >>>>> [New Thread 13304.0x3668]
> >>>>> [New Thread 13304.0xf4c]
> >>>>> [New Thread 13304.0x49c]
> >>>>> [New Thread 13304.0x1d4c]
> >>>>> [New Thread 13304.0x7fc]
> >>>>> [Thread 13304.0x7fc exited with code 0]
> >>>>> [New Thread 13304.0x357c]
> >>>>> [New Thread 13304.0x7c0]
> >>>>> [New Thread 13304.0x3564]
> >>>>> [New Thread 13304.0x26f4]
> >>>>> [New Thread 13304.0x2f68]
> >>>>>
> >>>>> Program received signal SIGSEGV, Segmentation fault.
> >>>>> 0x00007ffb9edea991 in ?? () from c:\qemu-master-msys2\libglib-2.0-0.dll
> >>>>> (gdb) bt
> >>>>> #0  0x00007ffb9edea991 in ?? () from
> >>>>> c:\qemu-master-msys2\libglib-2.0-0.dll
> >>>>> #1  0x000800000480bf50 in ?? ()
> >>>>> Backtrace stopped: previous frame inner to this frame (corrupt stack?)
> >>>>> (gdb)
> >>>>>
> >>>>> Even before I could attach to the process.
> >>>>
> >>>> If you run QEMU under gdb you don't have to attach to it but to get a
> >>>> meaningful backtrace you should configure and compile QEMU with
> >>>> --enable-debug (this will make it run slower so not recommended
> >>>> normally but for debugging that would be needed). If the stack is
> >>>> really corrupted then you may not get a useful backtrace or it may be
> >>>> a problem with gdb on Windows. I've found that gdb on Windows works
> >>>> for simple things but could give bad results for more complex stuff.
> >>>> WinDbg may be better but it's harder to use (needs some registry
> >>>> change I think to enable core dumps then you could open and analyze
> >>>> core dumps with it or it should be able to run command directly but I
> >>>> don't know how that works).
> >>>>
> >>>> Another idea: maybe you could check other threads in gdb. Not sure if
> >>>> that would reveal anything but may worth a try. I think the commands
> >>>> you need are "info threads" and "apply all bt" or something similar.
> >>>>
> >>>> Regards,
> >>>> BALATON Zoltan
> >>>>
> >>>
> >>> It looks to me the patch tires to recycle a temporary buffer to tap 
> >>> thread.
> >>>
> >>> Please try to attached fix to see it if works.
> >>
> >> Yep, good catch, thanks! This patch looks correct to me.
> >>
> >> Regards,
> >> Bin
> >
> > Hi,
> >
> > While the patch applies, it will not compile:
> >
> > ../net/tap-win32.c: In function 'tap_win32_send':
> > ../net/tap-win32.c:697:18: error: assignment to 'uint8_t' {aka
> > 'unsigned char'} from 'uint8_t *' {aka 'unsigned char *'} makes
> > integer from pointer without a cast [-Werror=int-conversion]
> >  697 |         orig_buf = buf;
> >      |                  ^
> > ../net/tap-win32.c:707:42: error: passing argument 2 of
> > 'tap_win32_free_buffer' makes pointer from integer without a cast
> > [-Werror=int-conversion]
> >  707 |         tap_win32_free_buffer(s->handle, orig_buf);
> >      |                                          ^~~~~~~~
> >      |                                          |
> >      |                                          uint8_t {aka unsigned char}
> > ../net/tap-win32.c:590:44: note: expected 'uint8_t *' {aka 'unsigned
> > char *'} but argument is of type 'uint8_t' {aka 'unsigned char'}
> >  590 |                                   uint8_t *pbuf)
> >      |                                   ~~~~~~~~~^~~~
>
> Patch missing a * from this line:
>
> +    uint8_t *buf, orig_buf;
>
> should be
>
> +    uint8_t *buf, *orig_buf;
>
> Regards,
> BALATON Zoltan

Hi all,

Together with that * from Zoltan, this patch restores tap networking in Windows.

Thanks!

So:
Tested-by: Howard Spoelstra <hsp.cat7@gmail.com>