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Re: [Qemu-devel] Re: software breakpoints disappearing/reappearing in KV
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From: |
Jan Kiszka |
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Subject: |
Re: [Qemu-devel] Re: software breakpoints disappearing/reappearing in KVM/qemu |
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Date: |
Sun, 10 Apr 2011 16:23:32 +0200 |
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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 |
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.
Jan
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