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Subject[PATCH v7 16/17] tracing: reserve $12(t0) for mcount-ra-address of gcc 4.5
Date
From: Wu Zhangjin <wuzhangjin@gmail.com>

A new option -mmcount-ra-address for gcc 4.5 have been sent by David
Daney <ddaney@caviumnetworks.com> in the thread "MIPS: Add option to
pass return address location to _mcount", which help to record the
location of the return address(ra) for the function graph tracer of MIPS
to hijack the return address easier and safer. that option used the
$12(t0) register by default, so, we reserve it for it, and use t1,t2,t3
instead of t0,t1,t2.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
---
arch/mips/kernel/mcount.S | 26 +++++++++++++-------------
1 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index bdfef2c..522e91c 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -65,8 +65,8 @@ NESTED(ftrace_caller, PT_SIZE, ra)
_mcount:
b ftrace_stub
nop
- lw t0, function_trace_stop
- bnez t0, ftrace_stub
+ lw t1, function_trace_stop
+ bnez t1, ftrace_stub
nop

MCOUNT_SAVE_REGS
@@ -93,21 +93,21 @@ ftrace_stub:
#else /* ! CONFIG_DYNAMIC_FTRACE */

NESTED(_mcount, PT_SIZE, ra)
- lw t0, function_trace_stop
- bnez t0, ftrace_stub
+ lw t1, function_trace_stop
+ bnez t1, ftrace_stub
nop
- PTR_LA t0, ftrace_stub
- PTR_L t1, ftrace_trace_function /* Prepare t1 for (1) */
- bne t0, t1, static_trace
+ PTR_LA t1, ftrace_stub
+ PTR_L t2, ftrace_trace_function /* Prepare t2 for (1) */
+ bne t1, t2, static_trace
nop

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
- PTR_L t2, ftrace_graph_return
- bne t0, t2, ftrace_graph_caller
+ PTR_L t3, ftrace_graph_return
+ bne t1, t3, ftrace_graph_caller
nop
- PTR_LA t0, ftrace_graph_entry_stub
- PTR_L t2, ftrace_graph_entry
- bne t0, t2, ftrace_graph_caller
+ PTR_LA t1, ftrace_graph_entry_stub
+ PTR_L t3, ftrace_graph_entry
+ bne t1, t3, ftrace_graph_caller
nop
#endif
b ftrace_stub
@@ -117,7 +117,7 @@ static_trace:
MCOUNT_SAVE_REGS

move a0, ra /* arg1: next ip, selfaddr */
- jalr t1 /* (1) call *ftrace_trace_function */
+ jalr t2 /* (1) call *ftrace_trace_function */
move a1, AT /* arg2: the caller's next ip, parent */

MCOUNT_RESTORE_REGS
--
1.6.2.1


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