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Commit e4240540 authored by Wu Zhangjin's avatar Wu Zhangjin Committed by Ralf Baechle
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MIPS: Tracing: Reduce the overhead of dynamic Function Tracer 



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: default avatarWu 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: default avatarRalf Baechle <ralf@linux-mips.org>
parent 4d6829f9

arch/mips/kernel/ftrace.c

+49 −44
Original line number Diff line number Diff line
@@ -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.
@@ -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)

{
@@ -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
@@ -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
@@ -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);

}
@@ -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;
@@ -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)