Re: [PATCH v3] MIPS: tracing: Optimize the implementation

[Wu Zhangjin <wuzhangjin@gmail.com>]

Hi,

This one fixed the building error ;)

Regards,
	Wu Zhangjin

On Sat, 2010-03-13 at 01:32 +0800, Wu Zhangjin wrote:
> From: Wu Zhangjin <wuzhangjin@gmail.com>
> 
> Changes:
> 
> v2 -> v3:
> 
>   + Fixes the buidling error of the changes from v2.
> 
> v1 -> v2:
> 
>   + Fixup the support of -mmcount-ra-address
> 
>     The offset of "b 1f" instruction should be 20 for leaf-function and
>     24 for non-leaf function when -mmcount-ra-address is enabled. This
>     patch adds a new get_insn_b_1f() function to get the different "b
>     1f" instruction.
> 
>   (only test without -mmcount-ra-address.)
> 
> v1:
> 
>   + Reduce the runtime overhead
> 
>     o Uses macros instead of variables for the fixed instructions to
>     reduce memory access
> 
>     o Moves the Initilization of the instructions which will be fixed
>     after linking from ftrace_make_nop/ftrace_make_call to
>     ftrace_dyn_arch_init() and encodes the instructions through
>     uasm(arch/mips/include/asm/uasm.h).
> 
>     o A common macro in_module() is defined to determine which space the
>     instruction pointer stays in and several related conditional
>     statements are converted to conditional operator(? :) statement.
> 
>   + Cleanup the whole stuff
> 
>     Lots of comments/macros have been cleaned up to let it look better.
> 
> Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
> ---
>  arch/mips/include/asm/ftrace.h |   12 ++-
>  arch/mips/kernel/ftrace.c      |  237 ++++++++++++++++++++++++----------------
>  2 files changed, 154 insertions(+), 95 deletions(-)
> 
> diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
> index ce35c9a..6dbfa1e 100644
> --- a/arch/mips/include/asm/ftrace.h
> +++ b/arch/mips/include/asm/ftrace.h
> @@ -3,7 +3,7 @@
>   * License.  See the file "COPYING" in the main directory of this archive for
>   * more details.
>   *
> - * Copyright (C) 2009 DSLab, Lanzhou University, China
> + * Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
>   * Author: Wu Zhangjin <wuzhangjin@gmail.com>
>   */
>  
> @@ -19,6 +19,14 @@
>  extern void _mcount(void);
>  #define mcount _mcount
>  
> +/*
> + * If the Instruction Pointer is in module space (0xc0000000), return true;
> + * otherwise, it is in kernel space (0x80000000), return false.
> + *
> + * FIXME: This may not work in some cases.
> + */
> +#define in_module(ip) (unlikely((ip) & 0x40000000))
> +
>  #define safe_load(load, src, dst, error)		\
>  do {							\
>  	asm volatile (					\
> @@ -83,8 +91,8 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  
>  struct dyn_arch_ftrace {
>  };
> +#endif /* CONFIG_DYNAMIC_FTRACE */
>  
> -#endif /*  CONFIG_DYNAMIC_FTRACE */
>  #endif /* __ASSEMBLY__ */
>  #endif /* CONFIG_FUNCTION_TRACER */
>  #endif /* _ASM_MIPS_FTRACE_H */
> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
> index e9e64e0..88e05ae 100644
> --- a/arch/mips/kernel/ftrace.c
> +++ b/arch/mips/kernel/ftrace.c
> @@ -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.
> @@ -15,15 +15,50 @@
>  #include <asm/cacheflush.h>
>  #include <asm/asm.h>
>  #include <asm/asm-offsets.h>
> +#include <asm/uasm.h>
> +
> +#define INSN_S_R_SP	0xafb00000	/* s{d,w} R, offset(sp) */
>  
>  #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)))
> +/* Before linking, the following instructions are fixed. */
> +#ifdef CONFIG_CPU_LOONGSON2F
> +#define INSN_NOP 0x00200825	/* or at, at, zero */
> +#else
> +#define INSN_NOP 0x00000000	/* nop */
> +#endif
> +#define INSN_B_1F_16 0x10000004	/* b 1f; offset = (16 >> 2) */
> +#define INSN_B_1F_20 0x10000005	/* b 1f; offset = (20 >> 2) */
> +#define INSN_B_1F_24 0x10000006	/* b 1f; offset = (24 >> 2) */
> +
> +/* After linking, the following instructions are fixed. */
> +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 __read_mostly;
> +
> +/* The following instructions are encoded in the run-time */
> +/* insn: jal func; op_code|addr : 31...26|25 ....0 */
> +#define INSN_JAL(addr) \
> +	((unsigned int)(0x0c000000 | (((addr) >> 2) & 0x03ffffff)))
> +
> +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);
>  
> -static unsigned int ftrace_nop = 0x00000000;
> +	/* jal (ftrace_caller + 8), jump over the first two instruction */
> +	buf = (u32 *)&insn_jal_ftrace_caller;
> +	uasm_i_jal(&buf, (FTRACE_ADDR + 8));
> +
> +	/* j ftrace_graph_caller */
> +	buf = (u32 *)&insn_j_ftrace_graph_caller;
> +	uasm_i_j(&buf, (unsigned long)ftrace_graph_caller);
> +}
>  
>  static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
>  {
> @@ -31,7 +66,6 @@ static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
>  
>  	/* *(unsigned int *)ip = new_code; */
>  	safe_store_code(new_code, ip, faulted);
> -
>  	if (unlikely(faulted))
>  		return -EFAULT;
>  
> @@ -40,118 +74,132 @@ static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
>  	return 0;
>  }
>  
> -static int lui_v1;
> -static int jal_mcount;
> +static inline unsigned int get_insn_b_1f(unsigned int *insn, unsigned long ip)
> +{
> +#ifndef KBUILD_MCOUNT_RA_ADDRESS
> +	*insn = INSN_B_1F_16;
> +	return 0;
> +#else
> +	int faulted;
> +	unsigned int code;
> +
> +	ip -= 4;
> +
> +	/* code = *(unsigned int *)ip; */
> +	safe_load_code(code, ip, faulted);
> +	if (unlikely(faulted))
> +		return -EFAULT;
> +
> +	if ((code & INSN_S_R_SP) != INSN_S_R_SP)
> +		*insn = INSN_B_1F_20;
> +	else
> +		*insn = INSN_B_1F_24;
> +
> +	return 0;
> +#endif
> +}
>  
>  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. */
> -	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;
> -		}
> -
> -		/* lui v1, hi_16bit_of_mcount        --> b 1f (0x10000004)
> -		 * addiu v1, v1, low_16bit_of_mcount
> -		 * move at, ra
> -		 * jalr v1
> -		 * nop
> -		 * 				     1f: (ip + 12)
> -		 */
> -		new = 0x10000004;
> -	} 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 = jump_insn_encode(JAL, (MCOUNT_ADDR + 8));
> -		}
> -
> -		/* move at, ra
> -		 * jalr v1		--> nop
> -		 */
> -		new = ftrace_nop;
> -	}
> +	/*
> +	 * We have compiled modules with -mlong-calls, but compiled kernel
> +	 * without it, therefore, need to cope with them respectively.
> +	 *
> +	 * For module:
> +	 *
> +	 *	lui	v1, hi16_mcount		--> b	1f
> +	 *	addiu	v1, v1, lo16_mcount
> +	 *	move	at, ra
> +	 *	jalr	v1
> +	 *	 nop
> +	 *					1f: (ip + 16)
> +	 * For kernel:
> +	 *
> +	 *	move	at, ra
> +	 *	jal	_mcount			--> nop
> +	 *
> +	 * And with the -mmcount-ra-address option, the offset may be 20 for
> +	 * leaf fuction and 24 for non-leaf function.
> +	 */
> +
> +	if (!in_module(ip))
> +		new = INSN_NOP;
> +	else if (get_insn_b_1f(&new, ip))
> +		return -EFAULT;
> +
>  	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, ftrace_nop);
> -	}
> -	/* ip, module: 0xc0000000, kernel: 0x80000000 */
> -	new = (ip & 0x40000000) ? lui_v1 : jal_mcount;
> +	new = in_module(ip) ? insn_lui_v1_hi16_mcount : insn_jal_ftrace_caller;
>  
>  	return ftrace_modify_code(ip, new);
>  }
>  
> -#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
> -
>  int ftrace_update_ftrace_func(ftrace_func_t func)
>  {
>  	unsigned int new;
>  
> -	new = jump_insn_encode(JAL, (unsigned long)func);
> +	new = INSN_JAL((unsigned long)func);
>  
> -	return ftrace_modify_code(FTRACE_CALL_IP, new);
> +	return ftrace_modify_code((unsigned long)(&ftrace_call), new);
>  }
>  
>  int __init ftrace_dyn_arch_init(void *data)
>  {
> +	ftrace_dyn_arch_init_insns();
> +
> +	/*
> +	 * We are safe to remove the "b ftrace_stub" for the current
> +	 * ftrace_caller() is almost empty (only the stack operations), and
> +	 * most importantly, the calling to mcount will be disabled later in
> +	 * ftrace_init(), then there is no 'big' overhead. And in the future,
> +	 * we are hoping the function_trace_stop is initialized as 1 then we
> +	 * can eventually remove that 'useless' "b ftrace_stub" and the
> +	 * following nop. Currently, although we can call ftrace_stop() to set
> +	 * function_trace_stop as 1, but it will change the behavior of the
> +	 * Function Tracer.
> +	 */
> +	ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);
> +
>  	/* The return code is retured via data */
>  	*(unsigned long *)data = 0;
>  
>  	return 0;
>  }
> -#endif				/* CONFIG_DYNAMIC_FTRACE */
> +#endif	/* CONFIG_DYNAMIC_FTRACE */
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  
>  #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)
>  {
> -	return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, ftrace_nop);
> +	return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
>  }
>  
> -#endif				/* !CONFIG_DYNAMIC_FTRACE */
> +#endif	/* !CONFIG_DYNAMIC_FTRACE */
>  
>  #ifndef KBUILD_MCOUNT_RA_ADDRESS
> -#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 */
> +#define INSN_S_RA_SP	0xafbf0000	/* s{d,w} ra, offset(sp) */
> +#define STACK_OFFSET_MASK	0xffff	/* stack offset range: 0 ~ PT_SIZE */
>  
>  unsigned long ftrace_get_parent_addr(unsigned long self_addr,
>  				     unsigned long parent,
> @@ -162,35 +210,35 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
>  	unsigned int code;
>  	int faulted;
>  
> -	/* 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;
> -	}
> +	/*
> +	 * For module, move the ip from calling site of mcount to the
> +	 * instruction "lui v1, hi_16bit_of_mcount"(offset is 20), but for
> +	 * kernel, move to the instruction "move ra, at"(offset is 12)
> +	 */
> +	ip = self_addr - (in_module(self_addr) ? 20 : 12);
>  
> -	/* search the text until finding the non-store instruction or "s{d,w}
> -	 * ra, offset(sp)" instruction */
> +	/*
> +	 * 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; */
>  		safe_load_code(code, ip, faulted);
> -
>  		if (unlikely(faulted))
>  			return 0;
>  
> -		/* If we hit the non-store instruction before finding where the
> +		/*
> +		 * 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)
> +		 * store the ra on the stack.
> +		 */
> +		if ((code & INSN_S_R_SP) != INSN_S_R_SP)
>  			return parent_addr;
> +	} while (((code & INSN_S_RA_SP) != INSN_S_RA_SP));
>  
> -	} while (((code & S_RA_SP) != S_RA_SP));
> -
> -	sp = fp + (code & OFFSET_MASK);
> +	sp = fp + (code & STACK_OFFSET_MASK);
>  
>  	/* ra = *(unsigned long *)sp; */
>  	safe_load_stack(ra, sp, faulted);
> @@ -211,16 +259,17 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
>  void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
>  			   unsigned long fp)
>  {
> +	int faulted;
>  	unsigned long old;
>  	struct ftrace_graph_ent trace;
>  	unsigned long return_hooker = (unsigned long)
>  	    &return_to_handler;
> -	int faulted;
>  
>  	if (unlikely(atomic_read(&current->tracing_graph_pause)))
>  		return;
>  
> -	/* "parent" is the stack address saved the return address of the caller
> +	/*
> +	 * "parent" is the stack address saved the return address of the caller
>  	 * of _mcount.
>  	 *
>  	 * if the gcc < 4.5, a leaf function does not save the return address
> @@ -241,12 +290,14 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
>  	if (unlikely(faulted))
>  		goto out;
>  #ifndef KBUILD_MCOUNT_RA_ADDRESS
> -	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)
> +	parent = (unsigned long *)ftrace_get_parent_addr(
> +			self_addr, old, (unsigned long)parent, fp);
> +
> +	/*
> +	 * If fails on getting the stack address of the non-leaf function's ra,
> +	 * stop function graph tracer and return
> +	 */
> +	if (unlikely(parent == 0))
>  		goto out;
>  #endif
>  	/* *parent = return_hooker; */
> @@ -272,4 +323,4 @@ out:
>  	ftrace_graph_stop();
>  	WARN_ON(1);
>  }
> -#endif				/* CONFIG_FUNCTION_GRAPH_TRACER */
> +#endif	/* CONFIG_FUNCTION_GRAPH_TRACER */