Re: Change call ABI on PA-RISC

[Helge Deller <deller@gmx.de>]

Hi Carlos,

On 14.11.2016 18:23, Carlos O'Donell wrote:
> On Mon, Nov 14, 2016 at 11:24 AM, Helge Deller <deller@gmx.de> wrote:
>> What I want to archieve is to modify the return pointer, in order
>> to be able to track when the function returns to his caller.
>> The kernel ftracer uses this then to generate call stacks and to
>> time the function.
>> Looking at the above code, it should then be possible for me
>> to modify -10(r3), but is there a guarantee that it's always at
>> -10(r3) and that r3 is used?
>> That's the reason I asked if we could modify mcount to
>> give the address (in the stack) of the return pointer, but maybe
>> it's just overkill for this use case ?
> 
> Why do you need to modify the value?
> 
> AFAICT ftrace uses these values heuristically e.g.
> HAVE_FUNCTION_GRAPH_FP_TEST, HAVE_FUNCTION_GRAPH_RET_ADDR_PTR?
> 
> For example the only uses I see are in ftrace_pop_return_trace() and
> they are purely heuristic.

Maybe I get you wrong, but do you suggest I don't need to implement
it because it's just heuristic ?
(I agree, it's not top priority, but nice to have nevertheless)

Helge