Re: [PATCH v7 2/3] arm64: implement ftrace with regs
From: Torsten Duwe <hidden>
Date: 2019-02-07 15:00:33
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On Thu, Feb 07, 2019 at 09:51:57AM -0500, Steven Rostedt wrote:
On Thu, 7 Feb 2019 10:33:50 +0000 Julien Thierry [off-list ref] wrote:quoted
I don't see really much documentation on that function. As far as I can tell it is only called once for each site (and if it didn't, we'd always be placing the same instruction, but I agree it wouldn't be nice). It could depend on how far you can expand the notion of "adjusting" :) . Steven, do you have an opinion on whether it would be acceptable to modify function entry code in ftrace_call_adjust() ?Just to make sure I'm on the same page as you are. You want to modify the function entry code at the time of the ftrace_call_adjust()?
Yes, this was the fiendish plan ;-)
I would update the rec->ip to the offset you want at ftrace_call_adjust() but not do any modifications. It really isn't safe to do it there. But right after that is called, you will have the arch specific call of ftrace_make_nop() called with MCOUNT_ADDR as the second parameter to let you know that this is the first time the call is made at this address. This is where you can do that initial modifications.
Ok, so just substitute REC_IP_BRANCH_OFFSET arithmetic with ftrace_call_adjust() and keep the MCOUNT_ADDR logic. Thanks for the clarification. Torsten _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel