Date: Fri, 3 Dec 2010 18:17:16 -0500 From: Jung-uk Kim <jkim@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r216161 - in head/sys: amd64/amd64 i386/i386 Message-ID: <201012031817.23834.jkim@FreeBSD.org> In-Reply-To: <201012031802.40083.jkim@FreeBSD.org> References: <201012032154.oB3LsADC035461@svn.freebsd.org> <201012031744.01956.jkim@FreeBSD.org> <201012031802.40083.jkim@FreeBSD.org>
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On Friday 03 December 2010 06:02 pm, Jung-uk Kim wrote: > On Friday 03 December 2010 05:43 pm, Jung-uk Kim wrote: > > On Friday 03 December 2010 05:08 pm, John Baldwin wrote: > > > On Friday, December 03, 2010 4:54:10 pm Jung-uk Kim wrote: > > > > Author: jkim > > > > Date: Fri Dec 3 21:54:10 2010 > > > > New Revision: 216161 > > > > URL: http://svn.freebsd.org/changeset/base/216161 > > > > > > > > Log: > > > > Explicitly initialize TSC frequency. To calibrate TSC > > > > frequency, we use DELAY(9) and it may use TSC in turn if TSC > > > > frequency is non-zero. > > > > > > We zero the BSS, so these were already zero. This just makes > > > the actual kernel file on disk larger by wasting space in .data > > > instead of .bss. > > > > Please note that I didn't touch other variables, e.g., > > tsc_is_broken, because I knew that. However, I just wanted to do > > that *explicitly*. Anyway, it is reverted now and SVN will > > remember what I wanted to do. ;-) > > > > BTW, if my memory serves, GCC (and all modern C compilers) put(s) > > zero-initialized variables back in .bss. > > I just tried it. GCC generates identical binaries as I thought. > However, Clang doesn't do the optimization. :-/ Strangely, Clang increases .bss when a global variable is explicitly initialized to zero. - 2 .bss 00000004 0000000000000000 0000000000000000 00000540 2**2 + 2 .bss 00000014 0000000000000000 0000000000000000 00000540 2**3 8-) Jung-uk Kim
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