GDB Python - gdb.execute() - with a timeout?

GDB Python - gdb.execute() - with a timeout?

[Duane Ellis]

Hi, am trying to script some times using GDB/Python specifically some test cases

The general format of my GDB_PY scripts are:

	import	gdb
	gdb.execute(“load foobar”)
	
	gdb.execute(“break test_breakpoint”)

	gdb.execute(“run”)
	gdb.execute(“set  test_flag=0x1234”)

	gdb.execute(“cont”)	 <— HERE Is where I want a timeout

	# At this point, we should eventually hit the “test_breakpoint”
	# However in some cases we do not.

the timeout needs to be ‘reasonably programable’ - i.e.:  1 second,  10 seconds, an hour would in some use cases be reasonable.

In other words, if my test case is running properly -  I should hit the breakpoint. 

I need a means to detect when things go wrong.

This problem is *NOT* limited to the TEST case

Is there some way to do this? 

Thanks.

Re: GDB Python - gdb.execute() - with a timeout?

[Ofir Cohen]

Hi,
This is achievable via pexpect wrapper.

You can take a look at this example:
http://opensource.apple.com/source/lldb/lldb-76/utils/test/disasm.py

The pexpect.spawn receives timeout as a parameter, so you could adapt it
to your needs.

I don't think this is achievable directly in gdb, i.e. w/o wrappers.
Most of the gdb code _once executed_ is synchronous and doesn't allow timeouts
or that sort of thing.

Correct me if I'm wrong.

- Ofir

On 27 July 2015 at 15:23, Duane Ellis <duane@duaneellis.com> wrote:
> Hi, am trying to script some times using GDB/Python specifically some test cases
>
> The general format of my GDB_PY scripts are:
>
>         import  gdb
>         gdb.execute(“load foobar”)
>
>         gdb.execute(“break test_breakpoint”)
>
>         gdb.execute(“run”)
>         gdb.execute(“set  test_flag=0x1234”)
>
>         gdb.execute(“cont”)      <— HERE Is where I want a timeout
>
>         # At this point, we should eventually hit the “test_breakpoint”
>         # However in some cases we do not.
>
> the timeout needs to be ‘reasonably programable’ - i.e.:  1 second,  10 seconds, an hour would in some use cases be reasonable.
>
> In other words, if my test case is running properly -  I should hit the breakpoint.
>
> I need a means to detect when things go wrong.
>
> This problem is *NOT* limited to the TEST case
>
> Is there some way to do this?
>
> Thanks.
>

Re: GDB Python - gdb.execute() - with a timeout?

[Duane Ellis]

> This is achievable via pexpect wrapper.

Thanks for the example but that won’t work for my situation - solution needs to run from within a GUI that has already wrapped GDB/LLDB in some form (for example eclipse). The pexpect solution - is external and controls GDB, in my scenario something else is already controlling GDB (i.e.: Eclipse or Emacs-GUD mode)

I have an idea - but don’t know how to implement parts of it
	After (X) timeout period I need to simulate pressing “control-C” via the gdb_python solution.

The idea is that Control_C at the GDB command console will cause GDB “cont” to stop - and send a “target halt” command and thus the gdb.excute(‘cont’) call will finish & return.

That would probably be sufficient for my purposes, the idea is sort of this:

Mainline thread:
    Set global “timeout period”
    FORK - creating new “timeout thread”
    perform  gdb.execute(“cont”)
    *CANCEL* the timeout thread.

Meanwhile,  timeout thread
     sleeps for “timeout period”
     After timeout period - ?? somehow ?? Simulate human pressing Control-C at the GDB console window

Some notes:
   (A) I know that GDB is single threaded
   (B) I know there is an ‘event queue’ or ‘work queue’
   (C) As I understand Python threads must “post” an event to a GDB event/work queue
   (D) Eventually when GDB is ‘safe’ that work item would be executed.

Assuming that work item is a call to a Python function, I don’t see how via Python the way to simulate “control-C” at the command console. 

Am I missing something?  Any suggestions?

Thanks.