Date: Wed, 17 Jan 2018 15:09:02 -0800 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Colin Percival <cperciva@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r327423 - in head/sys: kern sys Message-ID: <20180117230902.GP8113@FreeBSD.org> In-Reply-To: <201712310921.vBV9L133042419@repo.freebsd.org> References: <201712310921.vBV9L133042419@repo.freebsd.org>
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Hi Colin, On Sun, Dec 31, 2017 at 09:21:01AM +0000, Colin Percival wrote: C> Author: cperciva C> Date: Sun Dec 31 09:21:01 2017 C> New Revision: 327423 C> URL: https://svnweb.freebsd.org/changeset/base/327423 C> C> Log: C> Code for recording timestamps of events, especially function entries/exits. C> This is a very primitive system, intended for use in measuring performance C> during the early system boot, before more sophisticated tools like DTrace C> or infrastructure like kernel memory allocation and mutexes are available. C> C> Because this code records pointers to strings rather than copying strings C> (in order to keep the memory usage more manageable), if a kernel module is C> unloaded after logging an event, Bad Things can happen. Users are advised C> to not do that. C> C> Since cycle counts from the early kernel boot are used as an initial entropy C> source, publishing this information to userland could result in inadequate C> entropy being kept private to the kernel RNG. Users are advised to not C> enable this on systems with untrusted users. C> C> Discussed on: freebsd-current Sorry if my question is too lame and late. Why can't you use ktr(4) tracer for that purpose? The discussion on freebsd-current also doesn't have answer. -- Gleb Smirnoff
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