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Re: [Qemu-devel] Re: software breakpoints disappearing/reappearing in KV

From: Jan Kiszka
Subject: Re: [Qemu-devel] Re: software breakpoints disappearing/reappearing in KVM/qemu
Date: Sun, 10 Apr 2011 16:23:32 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2011-04-10 16:01, Avi Kivity wrote:
> On 04/08/2011 11:52 PM, Jan Kiszka wrote:
>> QEMU's gdbstub in KVM mode is simply not designed to account for guests
>> swapping out code pages that contain breakpoints. Due to the fact that
>> the Linux kernel does not do these weird things to its own code,
> It actually happily patches its own code at certain circumstances.  If
> you debug early boot or suspend/resume or cpu hotplug you're likely to
> encounter them.

Yes, it patches (alternates, jump_labels, mcount etc.), but it doesn't
swap or move code pages. At least so far.

If you need to break at such locations, there are still hardware
breakpoints, though only 4.


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