Commit 29c5d346 authored by Wu Zhangjin's avatar Wu Zhangjin Committed by Ralf Baechle

MIPS: Tracing: Add function graph tracer support for MIPS

The implementation of function graph tracer for MIPS is a little
different from X86.

in MIPS, gcc(with -pg) only transfer the caller's return address(at) and
the _mcount's return address(ra) to us.

For the kernel part without -mlong-calls:

move at, ra
jal _mcount

For the module part with -mlong-calls:

lui v1, hi16bit_of_mcount
addiu v1, v1, low16bit_of_mcount
move at, ra
jal _mcount

Without -mlong-calls,

if the function is a leaf, it will not save the return address(ra):

ffffffff80101298 <au1k_wait>:
ffffffff80101298:       67bdfff0        daddiu  sp,sp,-16
ffffffff8010129c:       ffbe0008        sd      s8,8(sp)
ffffffff801012a0:       03a0f02d        move    s8,sp
ffffffff801012a4:       03e0082d        move    at,ra
ffffffff801012a8:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff801012ac:       00020021        nop

so, we can hijack it directly in _mcount, but if the function is non-leaf, the
return address is saved in the stack.

ffffffff80133030 <copy_process>:
ffffffff80133030:       67bdff50        daddiu  sp,sp,-176
ffffffff80133034:       ffbe00a0        sd      s8,160(sp)
ffffffff80133038:       03a0f02d        move    s8,sp
ffffffff8013303c:       ffbf00a8        sd      ra,168(sp)
ffffffff80133040:       ffb70098        sd      s7,152(sp)
ffffffff80133044:       ffb60090        sd      s6,144(sp)
ffffffff80133048:       ffb50088        sd      s5,136(sp)
ffffffff8013304c:       ffb40080        sd      s4,128(sp)
ffffffff80133050:       ffb30078        sd      s3,120(sp)
ffffffff80133054:       ffb20070        sd      s2,112(sp)
ffffffff80133058:       ffb10068        sd      s1,104(sp)
ffffffff8013305c:       ffb00060        sd      s0,96(sp)
ffffffff80133060:       03e0082d        move    at,ra
ffffffff80133064:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff80133068:       00020021        nop

but we can not get the exact stack address(which saved ra) directly in
_mcount, we need to search the content of at register in the stack space
or search the "s{d,w} ra, offset(sp)" instruction in the text. 'Cause we
can not prove there is only a match in the stack space, so, we search
the text instead.

as we can see, if the first instruction above "move at, ra" is not a
store instruction, there should be a leaf function, so we hijack the at
register directly via putting &return_to_handler into it, otherwise, we
search the "s{d,w} ra, offset(sp)" instruction to get the stack offset,
and then the stack address. we use the above copy_process() as an
example, we at last find "ffbf00a8", 0xa8 is the stack offset, we plus
it with s8(fp), that is the stack address, we hijack the content via
writing the &return_to_handler in.

If with -mlong-calls, since there are two more instructions above "move
at, ra", so, we can move the pointer to the position above "lui v1,
hi16bit_of_mcount".
Signed-off-by: default avatarWu Zhangjin <wuzhangjin@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: zhangfx@lemote.com
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/677/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 8f99a162
......@@ -9,6 +9,7 @@ config MIPS
select HAVE_FUNCTION_TRACE_MCOUNT_TEST
select HAVE_DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_FUNCTION_GRAPH_TRACER
# Horrible source of confusion. Die, die, die ...
select EMBEDDED
select RTC_LIB if !MACH_LOONGSON
......
......@@ -13,6 +13,8 @@
#include <linux/ftrace.h>
#include <asm/cacheflush.h>
#include <asm/asm.h>
#include <asm/asm-offsets.h>
#ifdef CONFIG_DYNAMIC_FTRACE
......@@ -110,3 +112,107 @@ int __init ftrace_dyn_arch_init(void *data)
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
#define S_RA_SP (0xafbf << 16) /* s{d,w} ra, offset(sp) */
#define S_R_SP (0xafb0 << 16) /* s{d,w} R, offset(sp) */
#define OFFSET_MASK 0xffff /* stack offset range: 0 ~ PT_SIZE */
unsigned long ftrace_get_parent_addr(unsigned long self_addr,
unsigned long parent,
unsigned long parent_addr,
unsigned long fp)
{
unsigned long sp, ip, ra;
unsigned int code;
/* in module or kernel? */
if (self_addr & 0x40000000) {
/* module: move to the instruction "lui v1, HI_16BIT_OF_MCOUNT" */
ip = self_addr - 20;
} else {
/* kernel: move to the instruction "move ra, at" */
ip = self_addr - 12;
}
/* search the text until finding the non-store instruction or "s{d,w}
* ra, offset(sp)" instruction */
do {
ip -= 4;
/* get the code at "ip" */
code = *(unsigned int *)ip;
/* If we hit the non-store instruction before finding where the
* ra is stored, then this is a leaf function and it does not
* store the ra on the stack. */
if ((code & S_R_SP) != S_R_SP)
return parent_addr;
} while (((code & S_RA_SP) != S_RA_SP));
sp = fp + (code & OFFSET_MASK);
ra = *(unsigned long *)sp;
if (ra == parent)
return sp;
return 0;
}
/*
* Hook the return address and push it in the stack of return addrs
* in current thread info.
*/
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
unsigned long fp)
{
unsigned long old;
struct ftrace_graph_ent trace;
unsigned long return_hooker = (unsigned long)
&return_to_handler;
if (unlikely(atomic_read(&current->tracing_graph_pause)))
return;
/* "parent" is the stack address saved the return address of the caller
* of _mcount, for a leaf function not save the return address in the
* stack address, so, we "emulate" one in _mcount's stack space, and
* hijack it directly, but for a non-leaf function, it will save the
* return address to the its stack space, so, we can not hijack the
* "parent" directly, but need to find the real stack address,
* ftrace_get_parent_addr() does it!
*/
old = *parent;
parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old,
(unsigned long)parent,
fp);
/* If fails when getting the stack address of the non-leaf function's
* ra, stop function graph tracer and return */
if (parent == 0) {
ftrace_graph_stop();
WARN_ON(1);
return;
}
*parent = return_hooker;
if (ftrace_push_return_trace(old, self_addr, &trace.depth, fp) ==
-EBUSY) {
*parent = old;
return;
}
trace.func = self_addr;
/* Only trace if the calling function expects to */
if (!ftrace_graph_entry(&trace)) {
current->curr_ret_stack--;
*parent = old;
}
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
......@@ -93,6 +93,16 @@ NESTED(_mcount, PT_SIZE, ra)
PTR_L t1, ftrace_trace_function /* Prepare t1 for (1) */
bne t0, t1, static_trace
nop
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
PTR_L t2, ftrace_graph_return
bne t0, t2, ftrace_graph_caller
nop
PTR_LA t0, ftrace_graph_entry_stub
PTR_L t2, ftrace_graph_entry
bne t0, t2, ftrace_graph_caller
nop
#endif
b ftrace_stub
nop
......@@ -111,5 +121,37 @@ ftrace_stub:
#endif /* ! CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
NESTED(ftrace_graph_caller, PT_SIZE, ra)
MCOUNT_SAVE_REGS
PTR_LA a0, PT_R1(sp) /* arg1: &AT -> a0 */
move a1, ra /* arg2: next ip, selfaddr */
jal prepare_ftrace_return
move a2, fp /* arg3: frame pointer */
MCOUNT_RESTORE_REGS
RETURN_BACK
END(ftrace_graph_caller)
.align 2
.globl return_to_handler
return_to_handler:
PTR_SUBU sp, PT_SIZE
PTR_S v0, PT_R2(sp)
jal ftrace_return_to_handler
PTR_S v1, PT_R3(sp)
/* restore the real parent address: v0 -> ra */
move ra, v0
PTR_L v0, PT_R2(sp)
PTR_L v1, PT_R3(sp)
jr ra
PTR_ADDIU sp, PT_SIZE
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
.set at
.set reorder
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment