Hi Helge, On 2016-11-15, at 1:30 PM, Helge Deller wrote: > Hi Carlos, > > On 14.11.2016 18:23, Carlos O'Donell wrote: >> On Mon, Nov 14, 2016 at 11:24 AM, Helge Deller <deller@xxxxxx> 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) Probably, Carlos is referring to glibc code. Dave -- John David Anglin dave.anglin@xxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
