Re: [Qemu-devel] Add native debugger

["Andreas Färber" <afaerber@suse.de>]

Am 27.11.2011 15:12, schrieb Rick Hodgin:
> --- On Sun, 11/27/11, Blue Swirl <blauwirbel@gmail.com> wrote:
>> On Sun, Nov 27, 2011 at 04:10, Rick
>> Hodgin <foxmuldrster@yahoo.com>
>> wrote:
>>> For i386, I'm considering writing a native debugger
>> for QEMU that is not GDB. It would allow a separate/new
>> windowed interface which would show disassembly, registers,
>> stack, local variables, memory windows, etc., allowing the
>> user to single-step through code and trap opcodes like INT
>> 1, INT 3, INT 4, etc.  It would be invoked with something
>> like "qemu -debugger" from the command line, and would have
>> a UI similar to Microsoft's Debugger in Visual Studio when
>> no PDB is available, but would show a similar type of
>> disassembly form.
>>
>> QEMU and the debugger should be kept separate. You should
>> use the GDB interface to implement the debugger, that way
>> you can also test it against known good configuration. For
>> example, try to find out how GDB performs single stepping
>> (set remote debug 1).
> 
> I appreciate this advice. I'm looking for a native implementation within QEMU that is always available, always on, always active (when enabled). In this way, whenever INT 3 opcodes are found, the debugger can intercept and leap into existence, and without all of the gdb protocol overhead and parsing.

Still I don't think a new *debugger* is what you want for what you
describe. Take a look at target-i386/translate.c, that's where QEMU
decodes the opcodes. Note that this is code generation time, not
runtime, so that you either need to emit a call to a helper of yours
whenever that int 3 opcode is found and do your processing from that
helper or to realize your processing with just TCG instructions.

For displaying assembly instructions you could also surely reuse
existing tools from within your implementation, possibly i386-dis.c.

HTH,
Andreas

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