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>
index | next in thread | previous in thread | raw e-mail
[-- Attachment #1 --] Andriy Gapon <avg@FreeBSD.org> wrote: > on 10/06/2012 16:27 Fabian Keil said the following: > > Andriy Gapon <avg@FreeBSD.org> wrote: > > > >> It seems that the $subj is missing :-) > >> In my environment that causes many functions to not have fbt return probe, > >> 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. > > > > The patch seems to reduce the number of missing > > fbt return probes by about 50% for me. > > > > Without the patch: > > > > fk@r500 /usr/src $sudo dtrace -ln fbt::: | grep -c entry > > 23395 > > fk@r500 /usr/src $sudo dtrace -ln fbt::: | grep -c return > > 16739 > > > > With the patch (and updated kernel sources): > > > > fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c entry > > 23409 > > fk@r500 ~ $sudo dtrace -ln fbt::: | grep -c return > > 19879 > > 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 > > 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 functions > 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 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAk/U378ACgkQBYqIVf93VJ3bogCdHji0xGZCixxxcUhmTImxORzI tNEAoLigOjhi16L/CvR/w4vw8XnJeVlh =YNSV -----END PGP SIGNATURE-----help
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120610195611.5a8eeaec>