linux.git/arch/mips/kernel/mcount.S, branch v3.14

MIPS: Ftrace: Fix function tracing return address to match

2013-09-03T12:46:27+00:00

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 
[david.daney@cavium.com: Adjusted code comment and patch Subject.]
Signed-off-by: David Daney 
Cc: linux-mips@linux-mips.org
Cc: Steven Rostedt 
Signed-off-by: Ralf Baechle 
Patchwork: https://patchwork.linux-mips.org/patch/5592/

MIPS: kernel: mcount.S: Drop FRAME_POINTER codepath

2013-06-11T13:19:51+00:00

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

Signed-off-by: Markos Chandras 
Acked-by: Steven J. Hill 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5440/
Signed-off-by: Ralf Baechle

MIPS: Unbreak function tracer for 64-bit kernel.

2013-04-05T13:10:22+00:00

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 
Cc: linux-mips@linux-mips.org
Cc: Al Cooper 
Cc: viric@viric.name
Cc: stable@vger.kernel.org # 3.8.x
Signed-off-by: Ralf Baechle

MIPS: Function tracer: Fix broken function tracing

2013-01-31T14:28:48+00:00

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 
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

MIPS: tracing: Fix the indentation of mcount.S

2010-08-05T12:26:06+00:00

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 
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1475/
Signed-off-by: Ralf Baechle

MIPS: Tracing: Fix argument passing of the 32bit support with gcc 4.5

2010-07-05T16:17:28+00:00

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 
Cc: linux-mips 
Cc: David Daney 
Patchwork: http://patchwork.linux-mips.org/patch/1227/
Signed-off-by: Ralf Baechle

MIPS: Tracing: Cleanup comments

2010-07-05T16:17:27+00:00

Signed-off-by: Wu Zhangjin 
Cc: linux-mips 
Cc: David Daney 
Patchwork: http://patchwork.linux-mips.org/patch/1225/
Signed-off-by: Ralf Baechle

MIPS: Tracing: Cleanup the arguments passing of prepare_ftrace_return

2010-07-05T16:17:27+00:00

Signed-off-by: Wu Zhangjin 
Cc: linux-mips 
Cc: David Daney 
Patchwork: http://patchwork.linux-mips.org/patch/1226/
Signed-off-by: Ralf Baechle

MIPS: Tracing: Merge adjacent #ifdefs with same condition.

2010-07-05T16:17:27+00:00

Signed-off-by: Wu Zhangjin 
Cc: linux-mips 
Cc: David Daney 
Patchwork: http://patchwork.linux-mips.org/patch/1224/
Signed-off-by: Ralf Baechle

MIPS: Loongson: Change the Email address of Wu Zhangjin

2010-02-27T11:53:12+00:00

Currently wuzj@lemote.com is not usable; change it to wuzhangjin@gmail.com.

Signed-off-by: Wu Zhangjin 
Cc: linux-mips@linux-mips.org
Cc: yanh@lemote.com
Cc: huhb@lemote.com
Cc: zhangfx@lemote.com
Patchwork: http://patchwork.linux-mips.org/patch/829/
Signed-off-by: Ralf Baechle