[RFC] Target Layer Python Interface

[Jeff Mahoney]

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On 2/5/16 11:36 AM, Kieran Bingham wrote:
> 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/efba160691273ef3c154711255
4584088b5dba75
>>
>>
>>
>> 
(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

Ok, I have code doing that too.  There's a big messy commit at the top
of my repo last night that I'm going to refactor but I got most of
this working.

- -Jeff

> 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
> 


- -- 
Jeff Mahoney
SUSE Labs
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