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Date:      Sun, 10 Jun 2012 16:40:52 -0400
From:      Ryan Stone <rysto32@gmail.com>
To:        Andriy Gapon <avg@freebsd.org>
Cc:        freebsd-hackers@freebsd.org, Fabian Keil <freebsd-listen@fabiankeil.de>
Subject:   Re: decoding of multi-byte nops in dtrace
Message-ID:  <CAFMmRNwURMy55acPGZfYWnNSCB8VUvqWExV27RhBqcZHVUY==A@mail.gmail.com>
In-Reply-To: <4FD4CD8B.1080803@FreeBSD.org>
References:  <4FD490D5.1070207@FreeBSD.org> <20120610152721.3b627896@fabiankeil.de> <4FD4CD8B.1080803@FreeBSD.org>

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On Sun, Jun 10, 2012 at 12:38 PM, Andriy Gapon <avg@freebsd.org> wrote:
> Interesting observations, thank you.
> Do you use -O2 or higher optimization for kernel/modules build?
> I use only -O1.
>
> Here are some stats from my system:
> $ dtrace -ln fbt::: | fgrep -c entry
> 16876
> $ dtrace -ln fbt::: | fgrep -c return
> 16729
>
> So, 147 functions without return probe.

Try re-compiling with -foptimize-sibling-calls.  That enables the tail
call optimization in gcc, and therefore you get many functions with no
ret instruction (and thus no return probe in DTrace)



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