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

[Wu Zhangjin <wuzhangjin@gmail.com>]

On Wed, 2009-10-21 at 11:24 -0400, Steven Rostedt wrote:
> 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@lemote.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.

So, perhaps we can use the saved registers(a0,a1...) instead.

Regards!