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

To: wuzhangjin@gmail.com
Subject: Re: [PATCH -v4 9/9] tracing: add function graph tracer support for MIPS
From: Steven Rostedt <rostedt@goodmis.org>
Date: Wed, 21 Oct 2009 12:14:57 -0400
Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Thomas Gleixner <tglx@linutronix.de>, Ralf Baechle <ralf@linux-mips.org>, Nicholas Mc Guire <der.herr@hofr.at>
In-reply-to: <1256138506.11274.13.camel@falcon>
Organization: Kihon Technologies Inc.
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <028867b99ec532b84963a35e7d552becc783cafc.1256135456.git.wuzhangjin@gmail.com> <2f73eae542c47ac5bbb9f7280e6c0271d193e90d.1256135456.git.wuzhangjin@gmail.com> <3f0d3515f74a58f4cfd11e61b62a129fdc21e3a7.1256135456.git.wuzhangjin@gmail.com> <ea8aa927fbd184b54941e4c2ae0be8ea0b4f6b8a.1256135456.git.wuzhangjin@gmail.com> <96110ea5dd4d3d54eb97d0bb708a5bd81c7a50b5.1256135456.git.wuzhangjin@gmail.com> <5dda13e8e3a9c9dba4bb7179183941bda502604f.1256135456.git.wuzhangjin@gmail.com> <af3ec1b5cd06b6f6a461c9fa7d09a51fabccb08d.1256135456.git.wuzhangjin@gmail.com> <a6f2959a69b6a77dd32cc36a5c8202f97d524f1e.1256135456.git.wuzhangjin@gmail.com> <53bdfdd95ec4fa00d4cc505bb5972cf21243a14d.1256135456.git.wuzhangjin@gmail.com> <1256138506.11274.13.camel@falcon>
Reply-to: rostedt@goodmis.org
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On Wed, 2009-10-21 at 23:21 +0800, Wu Zhangjin wrote:

> > +unsigned long ftrace_get_parent_addr(unsigned long self_addr,
> > +                                unsigned long parent,
> > +                                unsigned long parent_addr,
> > +                                unsigned long fp)
> > +{
> > +   unsigned long sp, ip, ra;
> > +   unsigned int code;
> > +
> > +   /* move to the instruction "move ra, at" */
> > +   ip = self_addr - 8;
> > +
> > +   /* search the text until finding the "move s8, sp" instruction or
> > +    * "s{d,w} ra, offset(sp)" instruction */
> > +   do {
> > +           ip -= 4;
> > +           /* read the text we want to match */
> > +           if (probe_kernel_read(&code, (void *)ip, 4)) {
> > +                   WARN_ON(1);
> > +                   panic("read the text failure\n");
> > +           }
> > +
> > +           /* if the first instruction above "move at, ra" is "move
> > +            * s8(fp), sp", means the function is a leaf */
> > +           if ((code & MOV_FP_SP) == MOV_FP_SP)
> > +                   return parent_addr;
> > +   } while (((code & S_RA) != S_RA));
> > +
> > +   sp = fp + (code & STACK_OFFSET_MASK);
> > +   ra = *(unsigned long *)sp;
> > +
> 
> Seems missed the fault protection here? is there a need? never met fault
> in this place and also the following two places, so, are we safe to
> remove all of the fault protection?

Is that "sp" basically already been check by the above
probe_kernel_read? If so, then it should be fine not to do the check
again.

-- Steve

> 
> Regards
>       Wu Zhangjin
> 
> > +   if (ra == parent)
> > +           return sp;
> > +   else
> > +           panic
> > +               ("failed on getting stack address of ra\n: addr: 0x%lx, 
> > code: 0x%x\n",
> > +                ip, code);
> > +}
> > +


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