Re: [PATCH] [RFC] Fix for kvm qemu to return control to gdb stub on breakpoints

[Jan Kiszka <jan.kiszka@web.de>]

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Jerone Young wrote:
> This is mainly to try and fix the current debug state with using
> hardware breakpoints (until your software breakpoint work is ready for

Well, you may be lucky with hw-breakpoints on Intel, given userland is
patched. But if you aren't (IIRC, current code leaks debug register
settings outside the guest, e.g.), I wouldn't invest time here. The
debug register handling requires a rewrite in order to support proper
virtualization + guest debugging.

Right now I'm trying the clean up my debug patches and get things out:
 1. Reworked guest debug interface
 2. Fixed and enhanced userland support (including soft-BPs)
 3. debug register virtualization
 4. guest debugging with hw-breakpoints/watchpoints
I hope step 1 & 2 can be completed tonight, 3 & 4 finally over the weekend.

> primetime). I actually do need to submit another patch outside of this
> for initialization of some variables (which I see is in your patch too),
> as it ends up passing down garbage.

Yeah, that was another issue.

> 
> For now this is a patch mainly just to get qemu to break into the gdb
> stub when a debug interrupt comes in. Though I have a feeling more may
> be needed.

If you want to fix userland, you also have to ensure that the vcpu
thread that received the breakpoint doesn't continue to run - see my patch.

That said, if you have spare cycles left to spent on the debugging
thing, I would try to re-schedule my work and push some packages over to
your side. Just let me know! :)

Jan


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