[Qemu-devel] AArch64: QEMU fails in swapcontext

[Mian M. Hamayun]

Hello Peter & All,

I am trying to figure out a problem in qemu on aarch64 (with kvm enabled). I have found this problem in many different versions of qemu (v2.0.0-rc3/rc2/rc1/rc0, master 2d03b49), and I believe that either I am missing something common in all of these versions or its a genuine bug in qemu on aarch64.

The problem is triggered by virtqueue_notify() function (in virtio_ring.c) from the guest kernel and fails in the qemu_coroutine_new() while trying to do the swapcontext(&old_uc, &uc) (see coroutine-ucontext.c:164). The sigsetjmp(old_env, 0) just before the swapcontext() call seems to work fine, as it returns 0, and then we invoke the swapcontext().

The host kernel reports:
"qemu-system-aar[596]: bad frame in sys_rt_sigreturn: pc=004462e0 sp=7f8020f000" and kills the qemu process due to segmentation fault. The pc=004462e0 is for the coroutine_trampoline() but we don't actually reach it, when this particular crash happens.

Just to give you an idea of the code I am talking about:

$~/qemu[master]$ git blame -L 159,166 coroutine-ucontext.c
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 159)     makecontext(&uc, (void (*)(void))coroutine_trampoline,
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 160)                 2, arg.i[0], arg.i[1]);
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 161)
6ab7e546 (Peter Maydell 2013-02-20 15:21:09 +0000 162)     /* swapcontext() in, siglongjmp() back out */
6ab7e546 (Peter Maydell 2013-02-20 15:21:09 +0000 163)     if (!sigsetjmp(old_env, 0)) {
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 164)         swapcontext(&old_uc, &uc);
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 165)     }
00dccaf1 (Kevin Wolf    2011-01-17 16:08:14 +0000 166)     return &co->base;

My qemu configure/run commands are:

./configure --target-list=aarch64-softmmu       \
    --cross-prefix=aarch64-linux-gnu-           \
    --enable-fdt --enable-kvm --disable-werror  \
    --audio-drv-list="" --static

./qemu-system-aarch64 \
    -enable-kvm -nographic -kernel Image    \
    -drive if=none,file=disk_oe64.img,id=fs \
    -device virtio-blk-device,drive=fs      \
    -m 1024 -M virt -cpu host               \
    -append "earlyprintk console=ttyAMA0 mem=1024M rootwait root=/dev/vda rw init=/bin/sh"

Any ideas/comments on how to resolve this issue?

Best Regards,
Hamayun