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[Qemu-devel] Re: [5620] Add safety net against potential infinite loop
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: [5620] Add safety net against potential infinite loop |
Date: |
Wed, 05 Nov 2008 21:18:57 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
malc wrote:
> Revision: 5620
> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5620
> Author: malc
> Date: 2008-11-04 14:18:13 +0000 (Tue, 04 Nov 2008)
>
> Log Message:
> -----------
> Add safety net against potential infinite loop
>
> cpu_interrupt might be called while translating the TB, but before it
> is linked into a potentially infinite loop and becomes env->current_tb.
>
> Currently this can (and does) cause huge problems only when using
> dyntick clock, with other (periodic) clocks host_alarm_handler will
> eventually be executed resulting in a call to cpu_interrupt which will
> reset the recursion of running TB and the damage is "only" latency.
>
> Modified Paths:
> --------------
> trunk/cpu-exec.c
>
> Modified: trunk/cpu-exec.c
> ===================================================================
> --- trunk/cpu-exec.c 2008-11-04 13:17:17 UTC (rev 5619)
> +++ trunk/cpu-exec.c 2008-11-04 14:18:13 UTC (rev 5620)
> @@ -623,6 +623,14 @@
> }
> spin_unlock(&tb_lock);
> env->current_tb = tb;
> +
> + /* cpu_interrupt might be called while translating the
> + TB, but before it is linked into a potentially
> + infinite loop and becomes env->current_tb. Avoid
> + starting execution if there is a pending interrupt. */
> + if (unlikely (env->interrupt_request & CPU_INTERRUPT_EXIT))
> + env->current_tb = NULL;
> +
> while (env->current_tb) {
> tc_ptr = tb->tc_ptr;
> /* execute the generated code */
This somehow breaks single-stepping via gdbstub. Unless you have an
instant idea (or even fix), I will dig for the reasons.
Jan
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