Re: [PATCH 5/5] IA64 dynamic ftrace support

Keith Owens
2008-12-24T21:50:50Z

On Wed, 24 Dec 2008 08:29:05 -0500,
Steven Rostedt <srostedt@redhat.com> wrote:
>Yes I understand that the module and kernel code is set up differently,
>PPC is pretty much the same in this aspect. I'm asking if it is easy to
>change a call from the module to kernel core to another function in
>kernel core?
>
>Question: if I have a call from the module to _mcount, how much has to
>change in the set up of the registers to make it call ftrace_call
>instead? Perhaps we could link in a call to ftrace_call via the tricks
>in recordmcount.pl to get the info needed to make that change?

The IA64 kernel uses the same gp register throughout, it is compiled
with -mconstant-gp. So changing the target address from one kernel
function to another only requires changing the destination address in
the PLT stub, no other registers are affected.