The major reason for implementing the DWARF unwinder in the first place
was so that we could stop using __builtin_return_address(n), which
doesn't work on SH for n > 0.
Signed-off-by: NMatt Fleming <matt@console-pimps.org>

This is supposed to be the equivalent of __NR_syscalls, not
__NR_syscalls -1. The x86 code this was based on had simply fallen
out of sync at the time this was implemented. Fix it up now.

As a result, tracing of __NR_perf_counter_open works as advertised.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

Needed by ftrace changes in -tip.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

Add both dynamic and static function graph tracer support for sh.
Signed-off-by: NMatt Fleming <matt@console-pimps.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

It seems that MCOUNT_INSN_OFFSET was calculating the distance between
the wrong functions. The value that should have actually been computed
is the distance between ftrace_call and ftrace_stub. I discovered this
when I added some code to ftrace_caller.
Signed-off-by: NMatt Fleming <matt@console-pimps.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

Needed for dynamic ftrace API changes.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

First cut at dynamic ftrace support.
Signed-off-by: NMatt Fleming <mjf@gentoo.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

Impact: build fix for non-ftrace architectures

Not all archs implement ftrace, and therefore do not have an asm/ftrace.h.
This patch corrects the problem.

The ftrace_nmi_enter/exit now must be defined for all archs that implement
dynamic ftrace. Currently, only x86 does.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

This patch cleans up the NMI safe code for dynamic ftrace as suggested
by Andrew Morton.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: fix crashes that can occur in NMI handlers, if their code is modified

Modifying code is something that needs special care. On SMP boxes,
if code that is being modified is also being executed on another CPU,
that CPU will have undefined results.

The dynamic ftrace uses kstop_machine to make the system act like a
uniprocessor system. But this does not address NMIs, that can still
run on other CPUs.

One approach to handle this is to make all code that are used by NMIs
not be traced. But NMIs can call notifiers that spread throughout the
kernel and this will be very hard to maintain, and the chance of missing
a function is very high.

The approach that this patch takes is to have the NMIs modify the code
if the modification is taking place. The way this works is that just
writing to code executing on another CPU is not harmful if what is
written is the same as what exists.

Two buffers are used: an IP buffer and a "code" buffer.

The steps that the patcher takes are:

 1) Put in the instruction pointer into the IP buffer
    and the new code into the "code" buffer.
 2) Set a flag that says we are modifying code
 3) Wait for any running NMIs to finish.
 4) Write the code
 5) clear the flag.
 6) Wait for any running NMIs to finish.

If an NMI is executed, it will also write the pending code.
Multiple writes are OK, because what is being written is the same.
Then the patcher must wait for all running NMIs to finish before
going to the next line that must be patched.

This is basically the RCU approach to code modification.

Thanks to Ingo Molnar for suggesting the idea, and to Arjan van de Ven
for his guidence on what is safe and what is not.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This was missed with the ftrace support commit.. check it in now.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>