Date: Mon, 16 Sep 2013 08:52:01 +0200 From: Dimitry Andric <dim@FreeBSD.org> To: Adrian Chadd <adrian@freebsd.org> Cc: Ed Schouten <ed@80386.nl>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: -ffunction-sections, -fdata-sections and -Wl,--gc-sections Message-ID: <B432059E-24BD-4799-9060-A3692DF78477@FreeBSD.org> In-Reply-To: <CAJ-Vmok6kTizGaoxoAC5Gx0gDgpCYCSk3s4a%2BdhQsuTRZdBDaw@mail.gmail.com> References: <CAJOYFBBGY0GosPwG1B=1MKyapChEtX-O97r2zhXpGS8o7WO3gA@mail.gmail.com> <CAJ-Vmok6kTizGaoxoAC5Gx0gDgpCYCSk3s4a%2BdhQsuTRZdBDaw@mail.gmail.com>
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[-- Attachment #1 --] On Sep 16, 2013, at 03:08, Adrian Chadd <adrian@freebsd.org> wrote: >> The results are interesting. On amd64: >> >> - devd suddenly becomes 500 KB in size, instead of a megabyte, >> - init's size drops from 900 KB to 600 KB, >> - clang becomes a megabyte smaller. >> > > .. so, I'd like to know specific information as to why these three are now > smaller. So what's going on? This is simply unreferenced code and data being eliminated. It is quite normal for libraries (libc, the LLVM libs, etc) to contain functions that aren't called by the program you are linking. However, any .o file with multiple functions in it will be linked in as a whole, even if just one of the functions is called. I really think functions and data should always be separately "packaged" in object files, but for some reason this has never been the default for GNU tools, and everybody has apparently copied the behavior. :-) -Dimitry [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.20 (Darwin) iEYEARECAAYFAlI2qp0ACgkQsF6jCi4glqNK2QCgxv0f/dTe+zYeVvpnz0kZfu80 N98AoNrFoJIo0eKO4vL8cRE5i2tL/r9k =MnYI -----END PGP SIGNATURE-----
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