Re: [gentoo-user] bloated by gcc

[Daniel Troeder]

Am 28.09.2014 um 10:44 schrieb Jorge Almeida:
> I'm having a somewhat disgusting issue on my Gentoo: binaries are
> unaccountably large.
>
> I'm talking about C programs of my own, so no version related issues
> whatsoever. The computer is a core i3 with a 32 bit system.
>
> Example, for the same program:
>
> 10275 B on an atom running Slackware 14.1 (gcc 4.8.2)
> 5896 B (same, stripped with strip --strip-unneeded)
>
> 11675 B on i3, Gentoo, gcc 4.8.3 (with default gcc it was worse)
> 9704 B stripped
>
> 8207 B on *the same i3 box* running LFS (gcc 4.9.1)
> 5768 B stripped
>
> When compiling against dietlibc, the difference is even more shocking
> (almost double size in Gentoo after stripping).
>
> Compiled with:
> gcc -Os -march=i686  -fomit-frame-pointer -pipe -Wall -pedantic
> -fdata-sections -ffunction-sections -Wl,--gc-sections
> -fno-asynchronous-unwind-tables -std=c99
>
> Gentoo:
> $ gcc -v
> Using built-in specs.
> COLLECT_GCC=/usr/i686-pc-linux-gnu/gcc-bin/4.8.3/gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/i686-pc-linux-gnu/4.8.3/lto-wrapper
> Target: i686-pc-linux-gnu
> Configured with:
> /var/tmp/portage/sys-devel/gcc-4.8.3/work/gcc-4.8.3/configure
> --host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --prefix=/usr
> --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.8.3
> --includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.8.3/include
> --datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.8.3
> --mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.8.3/man
> --infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.8.3/info
> --with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.8.3/include/g++-v4
> --with-python-dir=/share/gcc-data/i686-pc-linux-gnu/4.8.3/python
> --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt
> --disable-werror --with-system-zlib --disable-nls
> --enable-checking=release --with-bugurl=https://bugs.gentoo.org/
> --with-pkgversion='Gentoo 4.8.3' --enable-libstdcxx-time
> --enable-shared --enable-threads=posix --enable-__cxa_atexit
> --enable-clocale=gnu --disable-multilib --disable-altivec
> --disable-fixed-point --with-arch=i686 --enable-targets=all
> --disable-libgcj --enable-libgomp --disable-libmudflap
> --disable-libssp --enable-lto --without-cloog
> Thread model: posix
> gcc version 4.8.3 (Gentoo 4.8.3)
>
> LFS:
> ##  gcc -v
> Using built-in specs.
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/i686-pc-linux-gnu/4.9.1/lto-wrapper
> Target: i686-pc-linux-gnu
> Configured with: ../gcc-4.9.1/configure --prefix=/usr
> --enable-languages=c,c++ --disable-multilib --disable-bootstrap
> --with-system-zlib
> Thread model: posix
> gcc version 4.9.1 (GCC)
>
> Slackware:
> Reading specs from /slash/usr/bin/../lib/gcc/i486-slackware-linux/4.8.2/specs
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/slash/usr/bin/../libexec/gcc/i486-slackware-linux/4.8.2/lto-wrapper
> Target: i486-slackware-linux
> Configured with: ../gcc-4.8.2/configure --prefix=/usr
> --libdir=/usr/lib --mandir=/usr/man --infodir=/usr/info
> --enable-shared --enable-bootstrap
> --enable-languages=ada,c,c++,fortran,go,java,lto,objc
> --enable-threads=posix --enable-checking=release --enable-objc-gc
> --with-system-zlib --with-python-dir=/lib/python2.7/site-packages
> --disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp
> --enable-lto --with-gnu-ld --verbose --enable-java-home
> --with-java-home=/usr/lib/jvm/jre --with-jvm-root-dir=/usr/lib/jvm
> --with-jvm-jar-dir=/usr/lib/jvm/jvm-exports --with-arch-directory=i386
> --with-antlr-jar=/root/slackware-current/source/d/gcc/antlr-runtime-3.4.jar
> --enable-java-awt=gtk --disable-gtktest --with-arch=i486
> --target=i486-slackware-linux --build=i486-slackware-linux
> --host=i486-slackware-linux
> Thread model: posix
> gcc version 4.8.2 (GCC)
>
> I'm not elfwise, but I could post something to google drive if needed.
>
> TIA
>
> Jorge Almeida
>
Hi :)

I have compared some exes and libs from Ubuntu 14.04 and my Gentoo (both
x86_64) and for similar versions it seems like most of _my_ Gentoo
binaries are around 10% bigger (a few are 10% smaller). I have
completely ignored GCC settings (both are 4.8.x though). IMO your sample
(one 5-10 kb program) is not representative for the distro in general.

I compared:
/bin/bash
/usr/bin/xterm
/bin/bzip2
/bin/gzip
/usr/bin/xz
/usr/bin/xev
/usr/lib/libaspell.so
/usr/lib/libdaemon.so

IMO you shouldn't compare 4.8.x with 4.9.x.

I don't want to dismiss your concern with your specific program. In your
case it is a big difference, and I'm curios too, where it comes from.

Maybe you can find out more by a more thorough comparation of the flags
GCC uses at runtime by comparing the output of:

gcc -Q <your flags (w/o -pipe)> --help=target
gcc -Q <your flags (w/o -pipe)> --help=optimizers

(Find more --help=____ in the man page.)


Greetings
Daniel


-- 
Get my PGP key at:
*
http://keyserver.ubuntu.com:11371/pks/lookup?op=get&search=0x837FB8B5BB9D4887
* $ gpg --recv-keys --keyserver keyserver.ubuntu.com 0xBB9D4887