Re: [Xen-devel] [PATCH] x86_emulate: properly do IP updates and other side effects on success

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 07/08/2014 15:24, Fabio Fantoni ha scritto:
> Il 07/08/2014 10:30, Jan Beulich ha scritto:
> > The two MMX/SSE/AVX code blocks failed to update IP properly, and these
> > as well as get_reg_refix(), which "manually" updated IP so far, failed
> > to do the TF and RF processing needed at the end of successfully
> > emulated instructions.
> >
> > Reported-by: Andrei LUTAS <vlutas@xxxxxxxxxxxxxxx>
> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > Tested-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Thanks for the patch, I tested it to see if solves also qxl on linux 
> domUs problem but with this patch the domU crashes and I cannot get a 
> backtrace or specific errors.
> xl create is ok, gdb on qemu close on domU's crash without having 
> backtrace and in xl dmesg I not saw errors.
> Setting preserve always in xl cfg I can only see that crash and do a 
> core dump but I not know how to use it to take a backtrace or any 
> other useful information.
> Someone can explain how to debug the problem for post all useful 
> informations please?
> In attachment for now I put xl -vvv create and xl dmesg output.
>
> Thanks for any reply and sorry for my bad english.
Now I also tried gdbsx:
gdbsx -a 2 64 9999
...
(gdb) target remote localhost:9999
Remote debugging using localhost:9999
[Switching to Remote target]
0x66666666 in ?? ()
(gdb) c
Continuing.

Program received signal SIGINT, Interrupt.
0x000000ff in ?? ()
(gdb) bt full
#0  0x000000ff in ?? ()
No symbol table info available.
Cannot access memory at address 0x6d2966c0

I not know if what I did is correct.

> > --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> > +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> > @@ -720,29 +720,26 @@ do{ uint8_t stub[] = { _bytes, 0xc3 };
> > put_fpu(&fic); \
> >   } while (0)
> >   -static unsigned long __get_rep_prefix(
> > -    struct cpu_user_regs *int_regs,
> > -    struct cpu_user_regs *ext_regs,
> > +static unsigned long _get_rep_prefix(
> > +    const struct cpu_user_regs *int_regs,
> >       int ad_bytes)
> >   {
> > -    unsigned long ecx = ((ad_bytes == 2) ? (uint16_t)int_regs->ecx :
> > -                         (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
> > -                         int_regs->ecx);
> > -
> > -    /* Skip the instruction if no repetitions are required. */
> > -    if ( ecx == 0 )
> > -        ext_regs->eip = int_regs->eip;
> > -
> > -    return ecx;
> > +    return (ad_bytes == 2) ? (uint16_t)int_regs->ecx :
> > +           (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
> > +           int_regs->ecx;
> >   }
> >     #define get_rep_prefix() 
> > ({                                             \
> >       unsigned long max_reps = 
> > 1;                                         \
> >       if ( rep_prefix() 
> > )                                                 \
> > -        max_reps = __get_rep_prefix(&_regs, ctxt->regs, 
> > ad_bytes);      \
> > +        max_reps = _get_rep_prefix(&_regs, 
> > ad_bytes);                   \
> >       if ( max_reps == 0 
> > )                                                \
> > -        goto 
> > done;                                                      \
> > - max_reps; \
> > + { \
> > +        /* Skip the instruction if no repetitions are required. 
> > */      \
> > +        dst.type = 
> > OP_NONE;                                             \
> > +        goto 
> > writeback;                                                 \
> > + } \
> > + max_reps; \
> >   })
> >     static void __put_rep_prefix(
> > @@ -3921,7 +3918,8 @@ x86_emulate(
> >           if ( !rc && (b & 1) && (ea.type == OP_MEM) )
> >               rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
> >                               ea.bytes, ctxt);
> > -        goto done;
> > +        dst.type = OP_NONE;
> > +        break;
> >       }
> >         case 0x20: /* mov cr,reg */
> > @@ -4188,7 +4186,8 @@ x86_emulate(
> >           if ( !rc && (b != 0x6f) && (ea.type == OP_MEM) )
> >               rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
> >                               ea.bytes, ctxt);
> > -        goto done;
> > +        dst.type = OP_NONE;
> > +        break;
> >       }
> >         case 0x80 ... 0x8f: /* jcc (near) */ {

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