Re: [PATCH] Python API: Add gdb.is_in_prologue and gdb.is_in_epilogue.

Doug Evans
2014-10-24T02:42:18Z

On Thu, Oct 23, 2014 at 11:13 AM, Daniel Gutson
<daniel.gutson@tallertechnologies.com> wrote:
> On Thu, Oct 23, 2014 at 3:09 PM, Martin Galvan
> <martin.galvan@tallertechnologies.com> wrote:
>> On Thu, Oct 23, 2014 at 2:57 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
>>> The fundamental problem is that the notion of "prologue" and "epilogue"
>>> simply no longer exists in optimized code generated by modern compilers;
>>> and even more compiler features get implemented that make those notions
>>> even less useful (e.g. shrink-wrapping).
>>>
>>> As a result, we have been trying to the rid of using those notions as
>>> much as possible; for example, when debugging optimized code with modern
>>> DWARF information present, GDB will today no longer even use prologue
>>> skipping at all. Instead, the debug information is good enough that
>>> the correct location of local variables can be recovered at every
>>> instruction in the function, making the distinction no longer needed.
>>>
>>> The in_prologue routine is likewise only still uses under certain rather
>>> rare circumstances; in fact it might even today be possible to simply
>>> remove it. Once more platforms provide correct DWARF covering epilogues
>>> as well, the gdbarch_in_function_epilogue_p calls in breakpoint.c may
>>> likewise become unnecessary.
>>>
>>> So if we hope at some point to get rid of those routines, then it seems
>>> counterproductive to now export them as part of a fixed external API ...
>>
>> While that may be true, it's also true that at some points we still
>> see the local variables having wrong values when stepping through
>> machine code. The aim of this patch is to expose a way of detecting
>> such situations for scripts that may need it. Until we have a safer
>> way to do it I think this should be integrated to the code base.
>
> Hi all,
> (Hi Pedro!)
>
> we badly need this. If you think the patch is in a shape good enough
> to be committed, please commit it for Martín since he doesn't have
> write access.
>
> We can then start a fresh new thread to discuss future directions
> specially related to optimized code and exactly what/how DWARF
> tags should be handled.

Ulrich raises a valid point though.
API design needs to be done with care.
I'd rather not rush this.