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MIPS: Tracing: Reduce the overhead of dynamic Function Tracer
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With the help of uasm this patch encodes the instructions of the dynamic
function tracer in ftrace_dyn_arch_init() when initializing it.

As a result we can remove the dynamic encoding of instructions in
ftrace_make_nop()/call(), ftrace_enable_ftrace_graph_caller() and remove
the macro jump_insn_encode() and at last this reduce the overhead of
dynamic Function Tracer.  This also is cleaner.

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/1230/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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Wu Zhangjin authored and Ralf Baechle committed Jul 5, 2010
1 parent 4d6829f commit e424054
Showing 1 changed file with 49 additions and 44 deletions.
93 changes: 49 additions & 44 deletions arch/mips/kernel/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
* Code for replacing ftrace calls with jumps.
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
* Copyright (C) 2009 DSLab, Lanzhou University, China
* Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
* Author: Wu Zhangjin <wuzhangjin@gmail.com>
*
* Thanks goes to Steven Rostedt for writing the original x86 version.
Expand All @@ -12,21 +12,46 @@
#include <linux/init.h>
#include <linux/ftrace.h>

#include <asm/cacheflush.h>
#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/uasm.h>

#ifdef CONFIG_DYNAMIC_FTRACE

#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */
#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */
#define jump_insn_encode(op_code, addr) \
((unsigned int)((op_code) | (((addr) >> 2) & ADDR_MASK)))

#define INSN_B_1F_4 0x10000004 /* b 1f; offset = 4 */
#define INSN_B_1F_5 0x10000005 /* b 1f; offset = 5 */
#define INSN_NOP 0x00000000 /* nop */
#define INSN_JAL(addr) jump_insn_encode(JAL, addr)
#define INSN_JAL(addr) \
((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))

static unsigned int insn_jal_ftrace_caller __read_mostly;
static unsigned int insn_lui_v1_hi16_mcount __read_mostly;
static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;

static inline void ftrace_dyn_arch_init_insns(void)
{
u32 *buf;
unsigned int v1;

/* lui v1, hi16_mcount */
v1 = 3;
buf = (u32 *)&insn_lui_v1_hi16_mcount;
UASM_i_LA_mostly(&buf, v1, MCOUNT_ADDR);

/* jal (ftrace_caller + 8), jump over the first two instruction */
buf = (u32 *)&insn_jal_ftrace_caller;
uasm_i_jal(&buf, (FTRACE_ADDR + 8));

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/* j ftrace_graph_caller */
buf = (u32 *)&insn_j_ftrace_graph_caller;
uasm_i_j(&buf, (unsigned long)ftrace_graph_caller);
#endif
}

static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
{
Expand All @@ -43,30 +68,20 @@ static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
return 0;
}

static int lui_v1;
static int jal_mcount;

int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
unsigned int new;
int faulted;
unsigned long ip = rec->ip;

/* We have compiled module with -mlong-calls, but compiled the kernel
* without it, we need to cope with them respectively. */
/*
* We have compiled module with -mlong-calls, but compiled the kernel
* without it, we need to cope with them respectively.
*/
if (ip & 0x40000000) {
/* record it for ftrace_make_call */
if (lui_v1 == 0) {
/* lui_v1 = *(unsigned int *)ip; */
safe_load_code(lui_v1, ip, faulted);

if (unlikely(faulted))
return -EFAULT;
}

#if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
/* lui v1, hi_16bit_of_mcount --> b 1f (0x10000005)
/*
* lui v1, hi_16bit_of_mcount --> b 1f (0x10000005)
* addiu v1, v1, low_16bit_of_mcount
* move at, ra
* move $12, ra_address
Expand All @@ -76,7 +91,8 @@ int ftrace_make_nop(struct module *mod,
*/
new = INSN_B_1F_5;
#else
/* lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
/*
* lui v1, hi_16bit_of_mcount --> b 1f (0x10000004)
* addiu v1, v1, low_16bit_of_mcount
* move at, ra
* jalr v1
Expand All @@ -86,36 +102,22 @@ int ftrace_make_nop(struct module *mod,
new = INSN_B_1F_4;
#endif
} else {
/* record/calculate it for ftrace_make_call */
if (jal_mcount == 0) {
/* We can record it directly like this:
* jal_mcount = *(unsigned int *)ip;
* Herein, jump over the first two nop instructions */
jal_mcount = INSN_JAL(MCOUNT_ADDR + 8);
}

/* move at, ra
* jalr v1 --> nop
/*
* move at, ra
* jal _mcount --> nop
*/
new = INSN_NOP;
}
return ftrace_modify_code(ip, new);
}

static int modified; /* initialized as 0 by default */

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned int new;
unsigned long ip = rec->ip;

/* We just need to remove the "b ftrace_stub" at the fist time! */
if (modified == 0) {
modified = 1;
ftrace_modify_code(addr, INSN_NOP);
}
/* ip, module: 0xc0000000, kernel: 0x80000000 */
new = (ip & 0x40000000) ? lui_v1 : jal_mcount;
new = (ip & 0x40000000) ? insn_lui_v1_hi16_mcount : insn_jal_ftrace_caller;

return ftrace_modify_code(ip, new);
}
Expand All @@ -133,6 +135,12 @@ int ftrace_update_ftrace_func(ftrace_func_t func)

int __init ftrace_dyn_arch_init(void *data)
{
/* Encode the instructions when booting */
ftrace_dyn_arch_init_insns();

/* Remove "b ftrace_stub" to ensure ftrace_caller() is executed */
ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);

/* The return code is retured via data */
*(unsigned long *)data = 0;

Expand All @@ -145,15 +153,12 @@ int __init ftrace_dyn_arch_init(void *data)
#ifdef CONFIG_DYNAMIC_FTRACE

extern void ftrace_graph_call(void);
#define JMP 0x08000000 /* jump to target directly */
#define CALL_FTRACE_GRAPH_CALLER \
jump_insn_encode(JMP, (unsigned long)(&ftrace_graph_caller))
#define FTRACE_GRAPH_CALL_IP ((unsigned long)(&ftrace_graph_call))

int ftrace_enable_ftrace_graph_caller(void)
{
return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
CALL_FTRACE_GRAPH_CALLER);
insn_j_ftrace_graph_caller);
}

int ftrace_disable_ftrace_graph_caller(void)
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