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

[Martin Galvan <martin.galvan@tallertechnologies.com>]

On Fri, Oct 24, 2014 at 5:09 PM, Pedro Alves <palves@redhat.com> wrote:
>> Well, I followed the code while testing a rather simple function and
>> noticed that handle_step_into_function is very similar (in terms of
>> the approach) to in_prologue plus some address corrections and setting
>> a breakpoint to proceed to. The API function needs only the address
>> calculation part.
>>
>> What if:
>>    1) I split handle_step_into_function in the address calc part and
>> the brakpoint insertion part,
>> moving the address calc to a new function (publicly available from infrun.h).
>>    2) I expose such function to the Python API.
>>
>> Would that be accepted? Would you want to see a patch?
>>
>> Please keep in mind that what I actually need is not really messing
>> with the prologue, but to know where the local variables are
>> accessible. If I could simply use DWARF info to accomplish that then I
>> wouldn't even touch the prologue at all.
>
> Hmm, how is this different from simply doing "break function" ?
> GDB sets function breakpoints after the prologue already.  A "step"
> into a function should stop at the exact same address as if the user
> did "b function; c" to run to said function.
>
> So, when you detect that you stepped into a function, you could
> just set the breakpoint by function name?

In order for that to work, I'd have to run the program up to that
point. I really need to be able to determine if at a given PC the
local variables will be accessible without actually running the
program. Ideally I'd use only DWARF info to know that.

I looked up the approach GDB takes when setting a breakpoint at a
function name. From what I saw it appears to be similar as the
"optimistic" path from in_prologue (that is, using symtab and line
info). I guess that makes sense since setting a breakpoint by function
name by definition requires us to have debugging info.

-- 

Martín Galván

Software Engineer

Taller Technologies Argentina

San Lorenzo 47, 3rd Floor, Office 5

Córdoba, Argentina

Phone: 54 351 4217888 / +54 351 4218211