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

From: Avi Kivity
Subject: Re: [Qemu-devel] Re: software breakpoints disappearing/reappearing in KVM/qemu
Date: Sun, 10 Apr 2011 17:41:24 +0300
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On 04/10/2011 05:23 PM, Jan Kiszka wrote:
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.

Try using modules (though that's different - the virtual addresses will change too). Or debugging a mixed kernel/user workload.

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


error compiling committee.c: too many arguments to function

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