hi, Steven > Note, PowerPC uses a trampoline from modules to kernel core. I think MIPS > just calls mcount differently. That is, it does a full 32bit address call > (64 bit for 64 bit archs?). Something like: > > lui v1, _mcount > addiu v1, v1, _mcount > jalr v1 > addiu sp, sp, -8 > > Then a nop would not do. Due to preemption, we can not modify more than > one line. But you could modify it to: > > b 1f > addiu v1, v1, _mcount > jalr v1 > addiu sp, sp, -8 > 1: > > Clobbering v1 should not be an issue since it is already used to store > _mcount. That is, we still do the addiu v1,v1,_mcount with that branch. > But v1 should be ignored. > sorry, I'm not clear what you said above, could you give more explanation on it, thanks! I think "jal _mcount" itself will not work in static and dynamic ftrace. something like what you described above should be used instead. perhaps a PATCH can be sent to gcc or we use some tricks in kernel. if we not use the method of modifying the kernel code in run time(avoid preemption?), can we link something as following to the modules: _mcount_trampoline: PTR_LA t0, _mcount jalr t0 and then we replace the original "jal _mcount" in every module to "jal _mcount_trampoline" with a perl script. this solution maybe work for static ftrace. does it? but in dynamic ftrace, when ftrace is enabled and set_filter_function is set, the place of filtered function will be substituted to "jal ftrace_caller", this will not work since ftrace_caller is a function like _mcount, which will not reached in modules. so, this ftrace_caller should be substituted to something like this: ftrace_caller_trampoline: PTR_LA t0, ftrace_caller jalr t0 and ftrace_caller_trampoline should be linked to modules too. or we substituted it to the above _mcount_trampoline, but change "PTR_LA t0, _mcount" to "PTR_LA t0, ftrace_caller". does this work? thanks! Wu Zhangjin
