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[Qemu-discuss] Using gdb, how to step only one machine instruction after

From: Parfait Tokponnon
Subject: [Qemu-discuss] Using gdb, how to step only one machine instruction after vmrun instruction? ...so that I jump in the guest OS code
Date: Tue, 22 Mar 2016 14:40:47 +0100

Hello everybody,
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:
                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.

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