Re: QEMU on x64

[Christopher Caulfield <ctcaulfield@gmail.com>]

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Thanks folks! I went ahead and made a feature/issue request based on
Paolo's suggestion:
QEMU registers support on x64 (#510) · Issues · QEMU / QEMU · GitLab
<https://gitlab.com/qemu-project/qemu/-/issues/510>

Please let me know if someone has the cycles to support this.

-Christopher

On Mon, Aug 2, 2021 at 10:37 AM Alex Bennée <alex.bennee@linaro.org> wrote:

>
> Peter Maydell <peter.maydell@linaro.org> writes:
>
> > On Fri, 30 Jul 2021 at 19:05, Christopher Caulfield
> > <ctcaulfield@gmail.com> wrote:
> >> This is Christopher from the debugging experiences team at Microsoft
> focused on kernel debugging. I am reaching out with a few questions about
> QEMU on x64.
> >>
> >> Is it possible for the QEMU-x86-64 GDB Server to send the full set
> >> of x64 system registers (whether they are included in a separated
> >> system xml file or as part of the core registers xml file)?
> >
> > Do you mean "is it possible for somebody to write code for
> > QEMU to make it do that", or "does QEMU do it today if you pass
> > it the right command line option" ? The answer to the former
> > is "yes", to the latter "no". (If you want the debugger to
> > be able to write to the system registers this might be a little
> > trickier, mostly in terms of "auditing the code to make sure this
> > can't confuse QEMU if you change some sysreg under its feet.".)
> >
> >> e.g. System registers missing from i386-64bit.xml file
> >
> >> DWORD64 IDTBase;
> >> DWORD64 IDTLimit;
> >> DWORD64 GDTBase;
> >> DWORD64 GDTLimit;
> >> DWORD SelLDT;
> >> SEG64_DESC_INFO SegLDT;
> >> DWORD SelTSS;
> >> SEG64_DESC_INFO SegTSS;
> >>
> >> How can I access x64 MSR registers by using the QEMU-x86-64 GDB server?
> >>
> >> #define MSR_EFER 0xc0000080 // extended function enable register
> >
> > EFER is in the xml ("x64_efer") so should be already accessible.
> > For anything else you're going to need to write some code to
> > make it happen.
> >
> >>is there any plan to support reading/writing to MSRs via QEMU-x86-64
> >GDB server?
>
> Not at the moment but I am keen to see any eventual solution try to be
> generic rather than hardwired for one architecture. The ARM code
> currently builds custom XML from it's register descriptors to expose
> it's MSR registers to the gdbstub. Ideally architecture front ends
> should register their registers with a new subsystem which can then do
> the glue between gdbstub as well as other systems that also care about
> register values (logging, HMP, TCG plugins).
>
> That said I'm not going to block any patches that just fix up the
> current XML and target/i386/gdbstub code. I'm not familiar enough with
> what the internal register representation state is for x86 w.r.t to TCG
> and hypervisor based running modes.
>
> > Not that I know of. We'd be happy to review patches if you want to
> > write them.
> >
> > thanks
> > -- PMM
>
>
> --
> Alex Bennée
>

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