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Re: Re: [Qemu-devel] [PATCH] Fix to gdb - wrong translation block invali

From: Mulyadi Santosa
Subject: Re: Re: [Qemu-devel] [PATCH] Fix to gdb - wrong translation block invalidated when setting gdb breakpoints
Date: Sun, 1 Jan 2006 15:10:20 +0700
User-agent: KMail/1.5

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);
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 



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