Feb 152017

GCC on CygWin logoStill using my aging XP x64, I recently tried to compile a newer version of the GNU compiler collection (GCC) on my equally aging installation of [CygWin], v1.7.35(0.287/5/3). Reason is that I can no longer update CygWin itself, because the project did away with NT5.x compatibility, so now you need Windows Vista or 7 for the latest version. Given that CygWin uses a rolling release model, you can’t get any “in between” versions later on. Also, despite my best efforts to make use of the great work of Peter Castros’ [CygWin Timemachine], I still haven’t managed to get a later version of CygWin that still supports XP. The later versions all have some kind of massive problem with the bash/sh permanently crashing and coredumping. No idea what the reason is.

And even if it would work, I’d still be stuck with GCC 5.3.0 or 5.4.0 or something. It’s not that I absolutely need a fresh C/C++ compiler right now, but it’s good to be prepared, especially when it comes to the adoption of modern C++ standards. Since I’m doing my own Windows builds of libav and ffmpeg (also: For a new x265-based benchmark project similar to my old [x264 benchmark]), I wanted to be able to use a current version.

On Linux and BSD UNIX, compiling and using a new version of GCC is surprisingly simple! On CygWin however, it bombed for me trying to build the JNI (Java Native Interface), and after disabling it, it stumbled over some mysteriously missing files while I was following [this guide].

Luckily, a commenter named Joaquin provided a [solution] for this: CygWin seems to be missing some prerequisites that need to be downloaded. A script for doing that is included in the ./contrib/ folder of the unpacked GCC source tree, ./contrib/download_prerequisites! Let’s have a look inside:

  1. # Download some prerequisites needed by gcc.
  2. # Run this from the top level of the gcc source tree and the gcc
  3. # build will do the right thing.

Sounds useful… and:

  1. # Necessary to build GCC.
  2. MPFR=mpfr-2.4.2
  3. GMP=gmp-4.3.2
  4. MPC=mpc-0.8.1

Aha! So we’re missing “mpfr”, “gmp” and “mpc”. [mpfr] is a floating-point math library, [gmp] is another arithmetic library, and [mpc]… well, a math library as well. I have no idea why my CygWin would be missing those, or maybe it just doesn’t have the required versions? Uhm, and the following:

  1. # Necessary to build GCC with the Graphite loop optimizations.
  2. if [ "$GRAPHITE_LOOP_OPT" = "yes" ] ; then
  3.   ISL=isl-0.15

[ISL] is optional, but I guess it’s useful? I’m not actually sure what it really does though. Whatever it is, just call that helper script before the configuration stage, and everything should be fine. While sitting inside the root of the unpacked source tree, for GCC version 6.3.0 in my case (make SURE to choose a --program-suffix, or installation might effectively annihilate your platform compiler!), do something like this on your CygWin terminal:

./configure --program-suffix=-6.3.0 --enable-languages=c,c++ --disable-shared 
make -j12
make install

I’m limiting myself to C/C++ here. I don’t need Fortran (I think) and the JNI component of the Java stuff breaks on CygWin anyway, so we’ll leave Java out. Also, we’ll have no link-time optimization (lto), but the important stuff will be there. The C++ shared library is disabled and I built the thing with -j12 to spawn 12 threads (or is it processes?) for speeding up the build, since I have 12 logical CPUs.

And that’s it!

To test things, I recompiled ffmpeg-3.2.4 with the new GCC 6.3.0 + yasm 1.3.0, and everything turned out just fine after rolling out the resulting ffmpeg.exe including some necessary CygWin libraries (cygwin1.dll and cygiconv-2.dll):

.\ffmpeg.exe -version | find /V "configuration"
ffmpeg version 3.2.4 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 6.3.0 (GCC)
libavutil      55. 34.101 / 55. 34.101
libavcodec     57. 64.101 / 57. 64.101
libavformat    57. 56.101 / 57. 56.101
libavdevice    57.  1.100 / 57.  1.100
libavfilter     6. 65.100 /  6. 65.100
libswscale      4.  2.100 /  4.  2.100
libswresample   2.  3.100 /  2.  3.100
libpostproc    54.  1.100 / 54.  1.100

A quick test showed the ffmpeg binary can cleanly decode H.265/HEVC video and also other stuff like FLAC, so it’s looking good! :)

CC BY-NC-SA 4.0 Compiling and installing GCC on CygWin by The GAT at XIN.at is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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