From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keith Owens Date: Wed, 24 Dec 2008 21:50:50 +0000 Subject: Re: [PATCH 5/5] IA64 dynamic ftrace support Message-Id: <13196.1230155450@ocs14w> List-Id: References: <1230012500.10933.102.camel@sli10-desk.sh.intel.com> In-Reply-To: <1230012500.10933.102.camel@sli10-desk.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Wed, 24 Dec 2008 08:29:05 -0500, Steven Rostedt 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.