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Date: Sun, 10 Jun 2012 16:40:52 -0400
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From: Ryan Stone <rysto32@gmail.com>
To: Andriy Gapon <avg@freebsd.org>
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Cc: freebsd-hackers@freebsd.org, Fabian Keil <freebsd-listen@fabiankeil.de>
Subject: Re: decoding of multi-byte nops in dtrace
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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)