Every mcount() call in the MIPS 32-bit kernel is done as follows:

[...]
move at, ra
jal _mcount
addiu sp, sp, -8
[...]

but upon returning from the mcount() function, the stack pointer
is not adjusted properly. This is explained in details in 58b69401c797
(MIPS: Function tracer: Fix broken function tracing).

Commit ad8c396936e3 ("MIPS: Unbreak function tracer for 64-bit kernel.)
fixed the stack manipulation for 64-bit but it didn't fix it completely
for MIPS32.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: <stable@vger.kernel.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7792/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Pull MIPS updates from Ralf Baechle:
 "This is the main pull request for 3.17.  It contains:

   - misc Cavium Octeon, BCM47xx, BCM63xx and Alchemy  updates
   - MIPS ptrace updates and cleanups
   - various fixes that will also go to -stable
   - a number of cleanups and small non-critical fixes.
   - NUMA support for the Loongson 3.
   - more support for MSA
   - support for MAAR
   - various FP enhancements and fixes"

* 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus: (139 commits)
  MIPS: jz4740: remove unnecessary null test before debugfs_remove
  MIPS: Octeon: remove unnecessary null test before debugfs_remove_recursive
  MIPS: ZBOOT: implement stack protector in compressed boot phase
  MIPS: mipsreg: remove duplicate MIPS_CONF4_FTLBSETS_SHIFT
  MIPS: Bonito64: remove a duplicate define
  MIPS: Malta: initialise MAARs
  MIPS: Initialise MAARs
  MIPS: detect presence of MAARs
  MIPS: define MAAR register accessors & bits
  MIPS: mark MSA experimental
  MIPS: Don't build MSA support unless it can be used
  MIPS: consistently clear MSA flags when starting & copying threads
  MIPS: 16 byte align MSA vector context
  MIPS: disable preemption whilst initialising MSA
  MIPS: ensure MSA gets disabled during boot
  MIPS: fix read_msa_* & write_msa_* functions on non-MSA toolchains
  MIPS: fix MSA context for tasks which don't use FP first
  MIPS: init upper 64b of vector registers when MSA is first used
  MIPS: save/disable MSA in lose_fpu
  MIPS: preserve scalar FP CSR when switching vector context
  ...

Dynamic tracing of kernel modules is broken on 32-bit MIPS. When modules
are loaded, the kernel crashes when dynamic tracing is enabled with:
 cd /sys/kernel/debug/tracing
 echo > set_ftrace_filter
 echo function > current_tracer

1) arch/mips/kernel/ftrace.c
When the kernel boots, or when a module is initialized, ftrace_make_nop()
modifies every _mcount call site to eliminate the ftrace overhead.
However, when ftrace is later enabled for a call site, ftrace_make_call()
does not currently restore the _mcount call correctly for module call sites.
Added ftrace_modify_code_2r() and modified ftrace_make_call() to fix this.

2) arch/mips/kernel/mcount.S
_mcount assembly routine is supposed to have the caller's _mcount call site
address in register a0. However, a0 is currently not calculated correctly for
module call sites. a0 should be (ra - 20) or (ra - 24), depending on whether
the kernel was built with KBUILD_MCOUNT_RA_ADDRESS or not.

This fix has been tested on Broadcom BMIPS5000 processor. Dynamic tracing
now works for both built-in functions and module functions.

Signed-off-by: Petri Gynther <pgynther@google.com>
Cc: linux-mips@linux-mips.org
Cc: rostedt@goodmis.org
Cc: alcooperx@gmail.com
Cc: cminyard@mvista.com
Patchwork: https://patchwork.linux-mips.org/patch/7476/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Nothing sets function_trace_stop to disable function tracing anymore.
Remove the check for it in the arch code.

Cc: Ralf Baechle <ralf@linux-mips.org>
Tested-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Dynamic function tracing was not working on MIPS.  When doing dynamic
tracing, the tracer attempts to match up the passed in address with
the one the compiler creates in the mcount tables.  The MIPS code was
passing in the return address from the tracing function call, but the
compiler tables were the address of the function call.  So they
wouldn't match.

Just subtracting 8 from the return address will give the address of
the function call.  Easy enough.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
[david.daney@cavium.com: Adjusted code comment and patch Subject.]
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/5592/

CONFIG_FRAME_POINTER is not selectable for MIPS so this
codepath was never executed.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5440/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Commit 58b69401c797 [MIPS: Function tracer: Fix broken function tracing]
completely broke the function tracer for 64-bit kernels.  The symptom is
a system hang very early in the boot process.

The fix: Remove/fix $sp adjustments for 64-bit case.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: Al Cooper <alcooperx@gmail.com>
Cc: viric@viric.name
Cc: stable@vger.kernel.org # 3.8.x
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Function tracing is currently broken for all 32 bit MIPS platforms.
When tracing is enabled, the kernel immediately hangs on boot.
This is a result of commit b732d439cb43336cd6d7e804ecb2c81193ef63b0
that changes the kernel/trace/Kconfig file so that is no longer
forces FRAME_POINTER when FUNCTION_TRACING is enabled.

MIPS frame pointers are generally considered to be useless because
they cannot be used to unwind the stack. Unfortunately the MIPS
function tracing code has bugs that are masked by the use of frame
pointers. This commit fixes the bugs so that MIPS frame pointers
don't need to be enabled.

The bugs are a result of the odd calling sequence used to call the trace
routine. This calling sequence is inserted into every traceable function
when the tracing CONFIG option is enabled. This sequence is generated
for 32bit MIPS platforms by the compiler via the "-pg" flag.

Part of the sequence is "addiu sp,sp,-8" in the delay slot after every
call to the trace routine "_mcount" (some legacy thing where 2 arguments
used to be pushed on the stack). The _mcount routine is expected to
adjust the sp by +8 before returning.  So when not disabled, the original
jalr and addiu will be there, so _mcount has to adjust sp.

The problem is that when tracing is disabled for a function, the
"jalr _mcount" instruction is replaced with a nop, but the
"addiu sp,sp,-8" is still executed and the stack pointer is left
trashed. When frame pointers are enabled the problem is masked
because any access to the stack is done through the frame
pointer and the stack pointer is restored from the frame pointer when
the function returns.

This patch writes two nops starting at the address of the "jalr _mcount"
instruction whenever tracing is disabled. This means that the
"addiu sp,sp.-8" will be converted to a nop along with the "jalr".  When
disabled, there will be two nops.

This is SMP safe because the first time this happens is during
ftrace_init() which is before any other processor has been started.
Subsequent calls to enable/disable tracing when other CPUs ARE running
will still be safe because the enable will only change the first nop
to a "jalr" and the disable, while writing 2 nops, will only be changing
the "jalr". This patch also stops using stop_machine() to call the
tracer enable/disable routines and calls them directly because the
routines are SMP safe.

When the kernel first boots we have to be able to handle the gcc
generated jalr, addui sequence until ftrace_init gets a chance to run
and change the sequence. At this point mcount just adjusts the stack
and returns. When ftrace_init runs, we convert the jalr/addui to nops.
Then whenever tracing is enabled we convert the first nop to a "jalr
mcount+8". The mcount+8 entry point skips the stack adjust.

[ralf@linux-mips.org: Folded in  Steven Rostedt's build fix.]

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Cc: rostedt@goodmis.org
Cc: ddaney.cavm@gmail.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/4806/
Patchwork: https://patchwork.linux-mips.org/patch/4841/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

The commit "MIPS: Tracing: Cleanup the arguments passing of
prepare_ftrace_return" has moved the "jal     prepare_ftrace_return"
instruction after the handling of the 3rd argument but forgot to remove
the superfluous space before the related instructions.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1475/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

As documented in the GCC 4.5 docs [1] -mmcount-ra-address uses register
$12 to pass the stack offset of the return address to the _mcount function.
On 64-bit kernels $12 is t0 but in 32-bit kernels it is t4 so we need to
use $12 instead of t0 here to be correct for both kernel types.

[1] GCC documentation: MIPS Options
http://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips <linux-mips@linux-mips.org>
Cc: David Daney <david.s.daney@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/1227/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>