Re: [Xen-users] cygwin longjmp error on Xen guest - gs not restored?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Sep 16, 2009 at 06:11:23PM +1000, Mikel Ward wrote:
> Hi All
> 
> A colleague tells me there is a problem with Xen 3.0.3 on RHEL5 where
> Cygwin's bash fails to call longjmp() in a Windows guest.
> 
> The consensus is that Xen and KVM both had a bug, but that Xen has not
> yet fixed it.  Indeed I couldn't find any proof that it had been
> reported to Xen, hence this email.
>

You should post this to xen-devel. I don't think the developers will
notice it from xen-users.

-- Pasi

> Original KVM bug report:
> http://sourceforge.net/tracker/?func=detail&atid=893831&aid=1872255&group_id=180599
> 
> Test case:
> http://article.gmane.org/gmane.comp.emulators.kvm.devel/28099
> 
> #include <setjmp.h>
> 
>   jmp_buf env;
>   main()
>   {
>        if(setjmp(env)) return;
>        longjmp(env, 1);
>   }
> 
> More details: it's something to do with the GS register:
> http://markmail.org/message/5aqlqtrld4ti4gse
> 
> #include <stdio.h>
> 
> int main()
> {
>   unsigned short gs;
>   unsigned x;
> 
>   asm ("mov %%gs, %0\n" : "=g"(gs));
>   asm ("movl %%gs:0x30, %0\n" : "=r"(x));
> 
>   printf("gs: %x\n", gs);
>   printf("gs:0x30: %x\n", x);
> 
>   asm ("mov %0, %%gs\n" : : "g"(gs));
> 
>   printf("test\n");
> 
>   asm ("movl %%gs:0x30, %0\n" : "=r"(x));
> 
>   return 0;
> }
> 
> 
> KVM fix:
> http://article.gmane.org/gmane.comp.emulators.kvm.devel/28418
> 
> diff --git a/kernel/x86/vmx.c b/kernel/x86/vmx.c
> index 7507ce2..048460d 100644
> --- a/kernel/x86/vmx.c
> +++ b/kernel/x86/vmx.c
> @@ -910,6 +910,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 
> msr_index, u64 *pdata)
>               data = vmcs_readl(GUEST_SYSENTER_ESP);
>               break;
>       default:
> +             vmx_load_host_state(vcpu);
>               msr = find_msr_entry(to_vmx(vcpu), msr_index);
>               if (msr) {
>                       data = msr->data;
> 
> 
> Another related KVM thread:
> http://markmail.org/message/owy3x7pf6oywdx5e
> 
> Cygwin developers:
> http://www.cygwin.com/ml/cygwin/2009-05/msg00841.html
> http://www.cygwin.com/ml/cygwin/2008-08/msg00437.html
> 
> 
> I'll be happy to spend some time helping to test/diagnose if you can
> tell me what you need me to do.
> 
> Thanks
> 
> Mike
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users