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

Daniel Gutson
2014-10-23T18:14:01Z

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.

Thanks!

Daniel.

>
> --
>
> Martín Galván
>
> Software Engineer
>
> Taller Technologies Argentina
>
> San Lorenzo 47, 3rd Floor, Office 5
>
> Córdoba, Argentina
>
> Phone: 54 351 4217888 / +54 351 4218211

--

Daniel F. Gutson
Chief Engineering Officer, SPD

San Lorenzo 47, 3rd Floor, Office 5

Córdoba, Argentina

Phone: +54 351 4217888 / +54 351 4218211

Skype: dgutson