linux-kernel - Re: [PATCH -v4 4/9] tracing: add static function tracer support for MIPS

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Date:	Wed, 21 Oct 2009 11:24:46 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: [PATCH -v4 4/9] tracing: add static function tracer support
 for MIPS

On Wed, 2009-10-21 at 22:34 +0800, Wu Zhangjin wrote:

> +++ b/arch/mips/kernel/mcount.S
> @@ -0,0 +1,94 @@
> +/*
> + * the mips-specific _mcount implementation
> + *
> + * This file is subject to the terms and conditions of the GNU General Public
> + * License.  See the file "COPYING" in the main directory of this archive for
> + * more details.
> + *
> + * Copyright (C) 2009 DSLab, Lanzhou University, China
> + * Author: Wu Zhangjin <wuzj@...ote.com>
> + */
> +
> +#include <asm/regdef.h>
> +#include <asm/stackframe.h>
> +#include <asm/ftrace.h>
> +
> +	.text
> +	.set noreorder
> +	.set noat
> +
> +	/* since there is a "addiu sp,sp,-8" before "jal _mcount" in 32bit */
> +	.macro RESTORE_SP_FOR_32BIT
> +#ifdef CONFIG_32BIT
> +	PTR_ADDIU	sp, 8
> +#endif
> +	.endm
> +
> +	.macro MCOUNT_SAVE_REGS
> +	PTR_SUBU	sp, PT_SIZE
> +	PTR_S	ra, PT_R31(sp)
> +	PTR_S	AT, PT_R1(sp)
> +	PTR_S	a0, PT_R4(sp)
> +	PTR_S	a1, PT_R5(sp)
> +	PTR_S	a2, PT_R6(sp)
> +	PTR_S	a3, PT_R7(sp)
> +#ifdef CONFIG_64BIT
> +	PTR_S	a4, PT_R8(sp)
> +	PTR_S	a5, PT_R9(sp)
> +	PTR_S	a6, PT_R10(sp)
> +	PTR_S	a7, PT_R11(sp)
> +#endif
> +	.endm
> +
> +	.macro MCOUNT_RESTORE_REGS
> +	PTR_L	ra, PT_R31(sp)
> +	PTR_L	AT, PT_R1(sp)
> +	PTR_L	a0, PT_R4(sp)
> +	PTR_L	a1, PT_R5(sp)
> +	PTR_L	a2, PT_R6(sp)
> +	PTR_L	a3, PT_R7(sp)
> +#ifdef CONFIG_64BIT
> +	PTR_L	a4, PT_R8(sp)
> +	PTR_L	a5, PT_R9(sp)
> +	PTR_L	a6, PT_R10(sp)
> +	PTR_L	a7, PT_R11(sp)
> +#endif
> +	PTR_ADDIU	sp, PT_SIZE
> +.endm
> +
> +	.macro MCOUNT_SET_ARGS
> +	move	a0, ra		/* arg1: next ip, selfaddr */
> +	move	a1, AT		/* arg2: the caller's next ip, parent */
> +	PTR_SUBU a0, MCOUNT_INSN_SIZE
> +	.endm
> +
> +	.macro RETURN_BACK
> +	jr ra
> +	move ra, AT 
> +	.endm
> +
> +NESTED(_mcount, PT_SIZE, ra)
> +	RESTORE_SP_FOR_32BIT
> +	PTR_LA	t0, ftrace_stub
> +	PTR_L	t1, ftrace_trace_function /* please don't use t1 later, safe? */

Is t0 and t1 safe for mcount to use? Remember, mcount does not follow
the dynamics of C function ABI.

-- Steve


> +	bne	t0, t1, static_trace
> +	nop
> +
> +	j	ftrace_stub
> +	nop
> +
> +static_trace:
> +	MCOUNT_SAVE_REGS
> +
> +	MCOUNT_SET_ARGS			/* call *ftrace_trace_function */
> +	jalr	t1
> +	nop
> +
> +	MCOUNT_RESTORE_REGS
> +	.globl ftrace_stub
> +ftrace_stub:
> +	RETURN_BACK
> +	END(_mcount)
> +

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