Re: Using gdb, how to step only one machine instruction after vmrun instruction? ...so that I jump in the guest OS code

Re: Using gdb, how to step only one machine instruction after vmrun instruction? ...so that I jump in the guest OS code

[Parfait Tokponnon]

2016-03-23 14:45 GMT+01:00 Parfait Tokponnon <parfait.tokponnon@gmail.com>:
> Hello,
> I 'm using gdb to debug an hypervisor. and my goal is to trace the program
> execution starting from the point that the hypervisor launches the guest OS
> by "VMRUN" instruction so that I can jump to the first instruction in the
> guest OS code.
> This is an excerpt from the hypervisor code:
>                 clgi;
>                 sti;
>                 vmload;
>                 vmrun;  // starting from here, the cpu switch on
> virtualization and the Guest OS is fecthed
>                 vmsave; // this is the first instruction after a VMEXIT
>
> So, according to AMD documentation, the next instruction after VMRUN is at
> CS:RIP where CS and RIP are extracted from the VMCB specific field.
> But using gdb, when I step one instruction from VMRUN, the next instruction
> fechted by the debugger is the next instruction in the hypervisor code, that
> is "VMSAVE", not the OS code.
> So my problem is to trace the execution from the host code to the guest
> code.
> How can I do that? Is there anyone who faced such a kind of problem?
> Hope I can get help from YOU. Thanks
> --
> Parfait T.



-- 
Parfait T.

Using gdb, how to step only one machine instruction after vmrun instruction? ...so that I jump in the guest OS code

[Parfait Tokponnon]

Hello,
I 'm using gdb to debug an hypervisor. and my goal is to trace the
program execution starting from the point that the hypervisor launches
the guest OS by "VMRUN" instruction so that I can jump to the first
instruction in the guest OS code.
This is an excerpt from the hypervisor code:
                clgi;
                sti;
                vmload;
                vmrun;  // starting from here, the cpu switch on
virtualization and the Guest OS is fecthed
                vmsave; // this is the first instruction after a VMEXIT

So, according to AMD documentation, the next instruction after VMRUN
is at CS:RIP where CS and RIP are extracted from the VMCB specific
field.
But using gdb, when I step one instruction from VMRUN, the next
instruction fechted by the debugger is the next instruction in the
hypervisor code, that is "VMSAVE", not the OS code.
So my problem is to trace the execution from the host code to the guest code.
How can I do that? Is there anyone who faced such a kind of problem?
Hope I can get help from YOU. Thanks

-- 
Parfait T.