Date: Mon, 5 Jul 2010 17:12:42 +0000 (UTC) From: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-hackers@freebsd.org, Konstantin Belousov <kib@freebsd.org>, Navdeep Parhar <np@freebsd.org>, Peter Wemm <peter@freebsd.org> Subject: Re: elf obj load: skip zero-sized sections early Message-ID: <20100705171155.K14969@maildrop.int.zabbadoz.net> In-Reply-To: <4C320E6E.4040007@freebsd.org> References: <4C246CD0.3020606@freebsd.org> <20100702082754.S14969@maildrop.int.zabbadoz.net> <4C320E6E.4040007@freebsd.org>
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On Mon, 5 Jul 2010, Andriy Gapon wrote: > on 02/07/2010 11:29 Bjoern A. Zeeb said the following: >> On Fri, 25 Jun 2010, Andriy Gapon wrote: >> >> Hey, >> >>> Proposed patch skips zero sized sections without going into trouble of >>> allocating section entry (progtab), doing zero-sized memory allocs and >>> copies. >>> I observe that sometimes zero-sized set_pcpu sections are produced in >>> module >>> objects, maybe when a module doesn't create any per cpu data of its >>> one, but >>> references external pcpu data. Not sure. > [snip] >>> This work is based on np@'s investigation and original patch: >>> http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030093.html >>> >> >> Have you guys figured this out already? > > By 'this' - do you mean why that zero-sized section is produced at all? > Does it really matter why that happens? Well, no, I was thinking of the workaround and going ahead to commit somehting;) > I stated my guess already. Now I see that it is enough to simply include > sys/pcpu.h for this to happen. Inline assembly at the start of the said header > unconditionally creates the section. If DPCPU_DEFINE is never used in a module, > then set_pcpu section remains empty. Neither compiler nor linker have any reason > to drop empty sections in the build process for amd64 modules. > > I am not sure if ".section set_pcpu" assembly can be made conditional or moved > some place else, so that the section is only created when DPCPU_DEFINE is actually > used. The same applies to VIMAGE btw. Same technique. /bz -- Bjoern A. Zeeb From August on I will have a life. It's now up to you to do the maths and count to 64. -- Bondorf, Germany, 14th June 2010
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