linux-kernel - Re: [PATCH] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH

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Date:   Tue, 24 Jan 2017 00:43:19 +0000
From:   Abel Vesa <abelvesa@...il.com>
To:     Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
        viro@...iv.linux.org.uk,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        zhouchengming <zhouchengming1@...wei.com>
Subject: Re: [PATCH] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

Hi Jean-Jacques,

Here is the implementation I've made for ftrace_graph_regs_caller:

.macro __ftrace_graph_regs_caller

       sub     r0, fp, #4                          @ lr of
instrumented routine (parent)

       @ called from __ftrace_regs_caller
       ldr     r1, [sp, #56]                       @ instrumented routine (func)
       mcount_adjust_addr      r1, r1

       sub     r2, r0, #4                          @ frame pointer
       bl      prepare_ftrace_return

       ldr     lr, [sp, #64]                        @ restore lr from the stack
       ldmia   sp, {r0-r11, ip, sp}            @ restore r0 through sp
       ret     ip

.endm

AFAIK, you can still use fp (see the implementation without regs) since
it is an alternative name for r11. The FRAME_POINTER config options does
something else entirely and has nothing to do with what we need here.

I tested it but unfortunately, my current setup is with qemu and I don't have
a real hardware here close to test it properly. Could you please tell me if this
works on your setup?

Also the way I tested it was to comment out the code that uses the default
ftrace_graph_caller in ftrace_modify_graph_caller and enforced the usage of
the one with regs.

I will create a proper patch later today (I need to cleanup some stuff
first) and
send it.

Thanks,
Abel