Re: Re: [Qemu-devel] [PATCH] Fix to gdb - wrong translation block invalidated when setting gdb breakpoints

[Andre Pech <andre.pech@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2082 bytes --]

Hi Mulyadi,

The problem that you are running into here is that sys_uname has been
replaced by sys_newuname in kernel/sys.c. When I put a breakpoint in this
function, everything works correctly when I run uname in the virtual
machine.

I'm not sure I exactly understand your concern that breakpoints could be
missed. When you set the breakpoint, tb_invalidate_phys_page_range is
called, invalidating the translation block block for the address where you
are placing the breakpoint. At this point, the next time that the address is
hit, translate.c:gen_intermediate_code will have to be called, and the
breakpoint will be hit. Let me know if I've missed something here.

Thanks,
Andre

On 1/1/06, Mulyadi Santosa <a_mulyadi@softhome.net> wrote:
>
> Hello Andre...
>
> > Not a problem. I only started using qemu a month ago, so it took me a
> > while to get oriented in the code and understand what was going on. I
> > must say that I've been really impressed with qemu so far.
>
> There was an interesting case I had found recently. In Linux kernel for
> i386 arch, you will see that sys_uname is placed to return kernel
> version/name. Funny thing is, even if I use your patch (against qemu
> 0.7.1) and I put a breakpoint at sys_uname and issue "uname" at bash
> prompt, the Qemu VM doesn't stop. Can you kindly check it?
>
> NB: Please see target-i386/translate.c, there you will see lines like
> these (around line 6306):
> if (env->nb_breakpoints > 0) {
>             for(j = 0; j < env->nb_breakpoints; j++) {
>                 if (env->breakpoints[j] == pc_ptr) {
>                     gen_debug(dc, pc_ptr - dc->cs_base);
>                     break;
>                 }
>             }
>         }
> What I understand from this code is, VM is stop if breakpoint address
> matches with pc_ptr, which tb->pc and AFAIK that is the start address
> of the translation block. So in other word, in some cases Qemu might
> still miss the breakpoint (does it explain the sys_uname case?) Please
> CMIIW
>
> regards
>
> Mulyadi
>
>

[-- Attachment #2: Type: text/html, Size: 2959 bytes --]