Re: [RFC] Target Layer Python Interface

[Kieran Bingham <kieranbingham@gmail.com>]

On 04/02/16 22:16, Ales Novak wrote:
> Hello,
> 
> On 2016-2-1 19:19, Kieran Bingham wrote:
>> [...]
>> The API, I would expect to match that of the Target API operations. I
>> would expect a one-to-one mapping of (required) operation names to
>> perform functions.
>>
>> For instance, to support thread listings, I would expect something along
>> the lines of:
>>
>> .to_update_thread_list
>> .to_pid_to_str
>> .to_extra_thread_info
>> .to_thread_alive
>> .to_fetch_registers
>> ...
> 
> FTR I've slightly tweaked your gdb.Target to process "to_xfer_partial",
> the respective commit is:
> 
> https://github.com/alesax/gdb-kdump/commit/efba160691273ef3c1547112554584088b5dba75
> 
> 
> (and the respective branch is "gdb-target")
> 
> Then the target code which is accessing virtual (!) memory of the kernel
> dump on the disk (using libkdumpfile library) is as small as:
> 
> ===
> from gdb import Target
> from _kdumpfile import kdumpfile
> 
> class MyTarget(Target):
>     def __init__(self, fil):
>         self.kdump = kdumpfile(fil)
>         self.kdump.symbol_func = \
>             lambda nam: long(gdb.lookup_minimal_symbol(nam).value())
>         self.kdump.vtop_init()
>         super(MyTarget, self).__init__()
>     def to_xfer_partial(self, obj, annex, readbuf, writebuf, offset, ln):
>         if obj == self.TARGET_OBJECT_MEMORY:
>             r = self.kdump.read (self.kdump.KDUMP_KVADDR, offset, ln)
>             readbuf[:] = r
>         return ln
> 
> MyTarget(file("/tmp/vmcore"))
> ===
> 
> which is really nice, I'd say. Now it would be interesting

Were you going to say something else here? ... looks like it got chopped!


Pulling the const's through is pretty neat, and that does make an
effective way to implement the read overrides to a file!


By the way, I'd started to add thread support - but I'm on holiday now.

Adding an add_thread(pid,lwp,tid) method to the inferior allows

    def to_update_thread_list(self):
        gdb.write("LX.to_update_thread_list\n")
        inferior = gdb.selected_inferior()
        threads = inferior.threads()
        for task in tasks.task_lists():
            # Build ptid_t ... class object better here still
            ptid = (inferior.pid, 0, task['pid'])  # (pid, lwp, tid)
            if ptid not in threads:
                gdb.write("- New Task [{} {}]\n"
                          .format(task['pid'], task['comm'].string()))
                inferior.add_thread(ptid)


The 'if ptid not in tasks' is not working yet. That was going to be next
on my list.

I think the comparison function is in the wrong place, it should be
implementing __contains__ instead of compare I think.

Then it's just a matter of wiring up Jeff's Regcache ...

If you're interested: My latest patches are at:

http://git.linaro.org/people/kieran.bingham/binutils-gdb.git lkd-python

And the Kernel Awareness object is at
http://git.linaro.org/people/kieran.bingham/linux.git lkd-python

Feel free to have a go at wiring up while I'm away if it's useful to you.


> 
> 
>> And having seen Jeff's work today, we could utilise Jeff's py-regcache
>> object quite effectively
>>
>> [...]
>>
>> Yes, I suspect some of the functionality to implement will be very
>> repeatable throughout each of the operation call implementations.
>>
>>
>> However, the more I look into it - the more I see each function is
>> likely to need very specific bindings, as it is not simple passing from
>> c function to c function.
> 
> Yes, the mentioned to_xfer_partial being a good example (of not simple
> passing).

Indeed - but probably not too many hooks to implement to get thread
integration through python.

> 
>> Perhaps we can factor out commonality as we go - and try to keep as DRY
>> as possible, but I suspect it will be an iterative implementation
>> process.
>>
>>
>>> I can't comment without more details though. My initial reaction
>>> though is yeah, this sounds useful and exciting.
>>
>> Perfect :)
> 
> Yes, this definitely is worth pursuing.
> 

I'm glad you like the concept.
I think it can work well with the recent code Jeff has written.

Although I may be slightly diverted for a bit when I get back from
holiday - so if it can go somewhere for you guys ... do have a go until
I return. (And let me know how it goes!)

Regards

Kieran