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[Qemu-devel] Deterministic replay

From: Pavel Dovgaluk
Subject: [Qemu-devel] Deterministic replay
Date: Wed, 22 Dec 2010 14:20:01 +0300


 I am working on implementation of deteministic execution replay technology
for Qemu. It should be similar to VMWare's replay debugging.
 To make alarm timer (which invokes host_alarm_handler function)
determinisic, I changed it's behavior: it sets flag, that execution should
be stopped and this flag is checked before every instruction in the
translated code.
 To allow breaking the execution in any moment, I added flag check and
exit_tb call before every instruction.

 But there is one problem occurred: when I make the same actions like
gen_eob() function, Windows XP cannot load on emulated machine (it reboots
with GPF).
 But when I remove two of the actions, everything is OK. These actions are
the following:
    if (s->tb->flags & HF_INHIBIT_IRQ_MASK) {
    if (s->tb->flags & HF_RF_MASK) {

 What are these actions for? When I remove any of them the booting process
is OK.
 Please help me to understand interrupts mechanism or give links where to
read about it.

 I apply my modifications to version 0.12.3 of Qemu. Please refer to it.

Pavel Dovgaluk

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