Date: Sun, 10 Jun 2012 19:56:11 +0200 From: Fabian Keil <freebsd-listen@fabiankeil.de> To: Andriy Gapon <avg@FreeBSD.org> Cc: freebsd-hackers@FreeBSD.org Subject: Re: decoding of multi-byte nops in dtrace Message-ID: <20120610195611.5a8eeaec@fabiankeil.de> In-Reply-To: <4FD4CD8B.1080803@FreeBSD.org> References: <4FD490D5.1070207@FreeBSD.org> <20120610152721.3b627896@fabiankeil.de> <4FD4CD8B.1080803@FreeBSD.org>
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--Sig_/EdysLkl+sew/y3vrqCADOmZ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Andriy Gapon <avg@FreeBSD.org> wrote: > on 10/06/2012 16:27 Fabian Keil said the following: > > Andriy Gapon <avg@FreeBSD.org> wrote: > >=20 > >> It seems that the $subj is missing :-) > >> In my environment that causes many functions to not have fbt return pr= obe, > >> because function body decoding fails before 'ret' is found. > >> > >> Here is my attempt at fixing the problem: > >> http://people.freebsd.org/~avg/fbt-nop.patch > >> Reviews and suggestions are welcome. > >=20 > > The patch seems to reduce the number of missing > > fbt return probes by about 50% for me. > >=20 > > Without the patch: > >=20 > > fk@r500 /usr/src $sudo dtrace -ln fbt::: | grep -c entry > > 23395 > > fk@r500 /usr/src $sudo dtrace -ln fbt::: | grep -c return > > 16739 > >=20 > > With the patch (and updated kernel sources): > >=20 > > fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c entry > > 23409 > > fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c return > > 19879 >=20 > Interesting observations, thank you. > Do you use -O2 or higher optimization for kernel/modules build? Yes, I kept the default -O2. > I use only -O1. With -O1 (and your patch) I get: fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c entry 23421 fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c return 22621 > Here are some stats from my system: > $ dtrace -ln fbt::: | fgrep -c entry > 16876 > $ dtrace -ln fbt::: | fgrep -c return > 16729 >=20 > So, 147 functions without return probe. > >From a quick look at them they all seem to really never return. Either = they are > noreturn type such panic, or functions that always call the functions of = the > first type, or functions with endless loops in them such as top level fun= ctions > of many system threads. I looked at a couple of the functions that still lack return probes and the ones I looked at don't seem to belong into these categories. For example I get no return probes for g_eli_crypto_decrypt() and g_eli_crypto_encrypt(). Both return the return code of g_eli_crypto_cipher() for which I get a return probe. Fabian --Sig_/EdysLkl+sew/y3vrqCADOmZ Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAk/U378ACgkQBYqIVf93VJ3bogCdHji0xGZCixxxcUhmTImxORzI tNEAoLigOjhi16L/CvR/w4vw8XnJeVlh =YNSV -----END PGP SIGNATURE----- --Sig_/EdysLkl+sew/y3vrqCADOmZ--
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