Date: Sun, 19 Mar 2017 15:21:33 +0100 From: Tijl Coosemans <tijl@FreeBSD.org> To: Bruce Evans <brde@optusnet.com.au> Cc: Ed Maste <emaste@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r315522 - in head: contrib/binutils/ld/emulparams sys/conf Message-ID: <20170319152133.0921abd9@kalimero.tijl.coosemans.org> In-Reply-To: <20170319123107.W994@besplex.bde.org> References: <201703190022.v2J0MDhq015941@repo.freebsd.org> <20170319123107.W994@besplex.bde.org>
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On Sun, 19 Mar 2017 13:04:50 +1100 (EST) Bruce Evans <brde@optusnet.com.au> wrote: > On Sun, 19 Mar 2017, Ed Maste wrote: >> Log: >> use INT3 instead of NOP for x86 binary padding >> >> We should never end up executing the inter-function padding, so we >> are better off faulting than silently carrying on to whatever function >> happens to be next. >> >> Note that LLD will soon do this by default (although it currently pads >> with zeros). >> >> Reviewed by: dim, kib >> MFC after: 1 month >> Sponsored by: The FreeBSD Foundation >> Differential Revision: https://reviews.freebsd.org/D10047 > > Is this a pessimization? Instruction prefetch near the end of almost > every function now fetches INT3 instead of NOP. Both have to be > decoded to decoded whether to speculatively execute them. INT3 is > unlikely to be speculatively executed, but it takes extra work to > decide not to do so. I seem to vaguely remember that ud2 should be used to stop speculative execution (and the instruction fetching and possible cache invalidation because of it).home | help
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