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Subject: Re: [PATCH] MIPS: tracing: Optimize the implementation
From:   Wu Zhangjin <wuzhangjin@gmail.com>
Reply-To: wuzhangjin@gmail.com
To:     David Daney <ddaney@caviumnetworks.com>
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        Steven Rostedt <srostedt@redhat.com>, linux-mips@linux-mips.org
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Organization: DSLab, Lanzhou University, China
Date:   Fri, 12 Mar 2010 22:57:08 +0800
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On Fri, 2010-03-12 at 19:43 +0800, Wu Zhangjin wrote:
[...]
> Right, then, we can search the JAL or JALR, for kernel, will get it
> immediatly, for module, will only several instructions, we can do this
> searching in ftrace_make_nop and ftrace_make_call at run-time, but just
> found we can use the following function to do it in ftrace_init(), looks
> good.
> 
> static inline int is_call_mcount(unsigned int insn)
> {
> 	return ((insn & JAL) == JAL) || (insn == JALR_V1);
> }
> 
> static inline unsinged long mcount_callsite(unsigned long addr)
> {
> 	unsigned int insn;
> 
> 	insn = *(unsigned int *)addr; /*need safe_load_code*/
> 	if (is_call_mcount(insn))
> 		return addr;
> 
> 	do {
> 		addr += 4;	/* what about big endian? */
> 		insn = *(unsigned int *)addr; /*need safe_load_code*/
> 	} while (!is_call_mcount(insn));
> 

This is not possible for modules, for currently, the modules are not
loaded yet.

Regards,
	Wu Zhangjin