Re: [Qemu-devel] Crash due to invalid env->current_tb

[Alexander Graf]

On Apr 30, 2008, at 5:21 PM, Adam Lackorzynski wrote:

> On Wed Apr 30, 2008 at 17:11:32 +0200, Adam Lackorzynski wrote:
> > On Wed Apr 30, 2008 at 11:08:46 +0200, Alexander Graf wrote:
> > > There was a comment from Fabrice on how to do prologues in TCG to  
> > > save /
> > > restore the clobbered values. Btw, ebx gets clobbered as well.
> >
> > tcg/README says that some registers are clobbered. So something like
> > this should be safe:
> >
> > Index: cpu-exec.c
> > ===================================================================
> > --- cpu-exec.c  (revision 4276)
> > +++ cpu-exec.c  (working copy)
> > @@ -690,6 +691,15 @@
> >                 fp.ip = tc_ptr;
> >                 fp.gp = code_gen_buffer + 2 * (1 << 20);
> >                 (*(void (*)(void)) &fp)();
> > +#elif defined(__i386)
> > +               asm volatile ("push %%ebp\n"
> > +                             "push %%ebx\n"
> > +                             "call *%1\n"
> > +                             "pop %%ebx\n"
> > +                             "pop %%ebp\n"
> > +                             : "=a" (T0)
> > +                             : "r" (gen_func)
> > +                             : "esi", "edi", "ecx", "edx");
> > #else
> >                 T0 = gen_func();
> > #endif
>
> I just realised that the push and pop of ebx is not needed as T0 is  
> ebx
> which gets overwritten in the output anyway.

Why is T0 =a then? Shouldn't =a mean "input and output on eax for T0"?

> Index: cpu-exec.c
> ===================================================================
> --- cpu-exec.c  (revision 4276)
> +++ cpu-exec.c  (working copy)
> @@ -690,6 +691,13 @@
>                 fp.ip = tc_ptr;
>                 fp.gp = code_gen_buffer + 2 * (1 << 20);
>                 (*(void (*)(void)) &fp)();
> +#elif defined(__i386)
> +               asm volatile ("push %%ebp\n"
> +                             "call *%1\n"
> +                             "pop %%ebp\n"
> +                             : "=a" (T0)
> +                             : "r" (gen_func)
> +                             : "esi", "edi", "ecx", "edx");
> #else
>                 T0 = gen_func();
> #endif
>
>
> Adam
> --
> Adam                 address@hidden
>  Lackorzynski         http://os.inf.tu-dresden.de/~adam/