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Build

How to build GCC from source.

Tested with: version 5.1.0 on Ubuntu 14.04 in a 2013 computer.

Summary:

sudo apt-get build-dep gcc
# Required to compile gnat.
sudo apt-get install gnat-4.8
mkdir gcc
cd gcc
git clone git://gcc.gnu.org/git/gcc.git src
cd src
# No annotated tags... so no describe.
git checkout gcc-5_1_0-release
./contrib/download_prerequisites
cd ..
mkdir build
cd build
# C and C++ only.
../src/configure --enable-languages=c,c++ --prefix="$(pwd)/../install"
# Add a suffix to the executable names:
# --program-suffix="-4.7"
# All languages.
# ../src/configure --enable-languages=all --prefix="$(pwd)/../install"
# Wait hours.
make -j5
# Wait hours.
make check
# Install executables to /usr/local/bin
# There are also many other installed files under /usr/local.
sudo make install
gcc -v
# sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9

Or install locally for interactive testing:

make install DESTDIR="$(pwd)/../install"
cd ../install/usr/local/bin/
./gcc -v

Or configure to always install locally:

./configure --prefix="$(pwd)/../install"
# ...
make install
cd ../install/usr/local/bin/
./gcc -v

If you modify just the gcc/ directory, you can cd gcc; make; make install to touch only that directory.

Modify, rebuild and rerun

cat <<'EOS' | git apply -
diff --git a/gcc/gcc-main.c b/gcc/gcc-main.c
index 230ba48..01f87ef 100644
--- a/gcc/gcc-main.c
+++ b/gcc/gcc-main.c
@@ -37,9 +37,12 @@ along with GCC; see the file COPYING3.  If not see

 extern int main (int, char **);

+#include <stdlib.h>
+
 int
 main (int argc, char **argv)
 {
+  system("date > /tmp/gcc");
   driver d;

   return d.main (argc, argv);
EOS

cd build/gcc
make -j5
make -j5 install
cd ../install/usr/local/bin/
./gcc -v
cat /tmp/gcc

You cannot modify the stdout output with at puts("hacked), or else the build will fail! This probably happens because dumpspecs is used on some part of the bootstrap process.

Configure

https://gcc.gnu.org/install/configure.html

download_prerequisites

In Ubuntu 14.04, missing dependencies GMP and others did not go away for me even though they were installed with apt-get build-dep gcc and dpkg says they are present. I needed download_prerequisites

http://stackoverflow.com/questions/9253695/building-gcc-requires-gmp-4-2-mpfr-2-3-1-and-mpc-0-8-0

Also configure does not detect a missing flex, but it seems required or else you get a missing yylex error: http://stackoverflow.com/questions/4262531/trouble-building-gcc-4-6

Binutils and GCC

Binutils a requirement of GCC. For instance, Linux From Scratch first installs Binutils, then GCC, then recompiles both to bootstrap.

It appears that you can build both GCC and Binutils the same time: http://stackoverflow.com/questions/1726042/recipe-for-compiling-binutils-gcc-together This is called a combined build.

A compatibility matrix between GCC and Binutils can be found at: http://wiki.osdev.org/Cross-Compiler_Successful_Builds

glibc and GCC

GCC depends on glibc. TODO does it depend on stdlibc++?

Linux From Scratch compiles it twice to bootstrap.

Three systems

When you build GCC, you have to configure 3 systems:

  • build: where GCC will be built
  • host: the system that will run GCC
  • target: the system that will run the code generated by the compiled GCC

https://gcc.gnu.org/onlinedocs/gcc-5.1.0/gccint/Configure-Terms.html#Configure-Terms

Compilation options

../src/configure CFLAGS='-O0 -g' CXXFLAGS='-O0 -g'

The default compilation uses -O2, so you might want to reduce that for better debugging in development.

enable-languages

https://gcc.gnu.org/install/configure.html

By default, only some languages are built.

If you want to enable all languages, use:

--enable-languages=all

Gnat

ADA

gnat1

I am unable to to build and install it! http://www.linuxfromscratch.org/blfs/view/svn/general/gcc-ada.html

Apparently you need a super recent built GNAT as circular dependency, and that of Ubuntu 14.04 is not recent enough?

gccgo

Go

go1

I am unable to to build and install it!

https://golang.org/doc/install/gccgo

Build

Making a separate build directory is mandatory.

Took me 2 hours and a half on a and 5GB of disk.

To build only certain parts of GCC http://stackoverflow.com/questions/14728652/how-to-make-a-light-build-of-gcc-with-language-supports-etc-pruned:

../src/configure --enable-languages=c,c++

With make -j5, this took 1 hour.

See all configuration options with:

./configure --help

bootstrap

Build stages

By default, the build happens in 3 stages:

  1. compile the compiler with the compiler of the build computer
  2. use the compiled compiler to compile itself
  3. repeat 2. and compare 2 and 3. Should be the same.

Configure the build to disable bootstrap and compile only once:

../src/configure --disable-bootstrap

TODO does it work without? Is bootstrap really necessary? How can stage 3 ever be different from stage 2?

Tests

check

Requires:

sudo apt-get install autogen runtest

Run all tests:

make -k check

Run only certain tests:

make -k check-gcc-c
make -k check-gcc

Restrict to tests under a single directory gcc/testsuite/gcc.dg:

make check-gcc RUNTESTFLAGS='dg.exp'

where dg.exp is a test script in that directory.

Run a single test:

make check-gcc RUNTESTFLAGS='dg.exp=cast-1.c'

Where cast-1.c refers to gcc/testsuite/gcc.dg/cast-1.c

Run tests matching glob:

make check-gcc RUNTESTFLAGS='dg.exp=cast-*.c'

Test output is very noisy, and does not return non zero on failure.

You should look for a line of type:

        === gcc Summary ===

# of expected passes        16
# of unexpected failures    2

for failures, or read the .sum file under build/gcc/testsuite/gcc.

Known failures exist in all versions, and are summarized at: https://gcc.gnu.org/gcc-5/buildstat.html

Executables are compiled under: build/gcc/testsuite/gcc. That also contains:

  • a .log file with detailed test information
  • a .sum file with summary pass / fail information

Tests are run with runtest, which uses expect:

  • runtest is part of DejaGnu. Thus the .dg directories.
  • .exp files are expect scripts

Install

By default, generated files will be put under:

  • /usr/local/bin: for front-end executables like gcc, ld
  • /usr/local/lib64: for libraries like libstdc++
  • /usr/local/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0: for backend executables like cc1 and collect2

GCC knows how to find the correct internal executables like cc1 even if they are not in your path. Configure path information must be hard-coded into it.

Run what you've built

TODO what is the required glibc for each GCC?

C programs seemed to run directly:

gcc hello_world.c
./hello_world

On Ubuntu 14.04, GCC 5.1, C++ programs needed $LD_LIBRARY_PATH to find the standard library libstdc++.so as it is not on the path by default:

LD_LIBRARY_PATH="/usr/local/lib64:$LD_LIBRARY_PATH" ./cpp

Uninstall

There is not top-level uninstall target that removes everything, but some subtrees do have the target.

Remove installations from the gcc/ tree:

cd gcc
sudo make uninstall

Documentation

make

builds man and info documentation by default:

cd gcc/doc
man ./gcc.1

Those are generated from the .texi inputs.

For the HTML docs, use:

make html

firefox/gcc/HTML/gcc-4.8.2/gcc/index.html

The website is not included in the source code, but on a separate repo:

cvs -q -d :pserver:[email protected]:/cvs/gcc checkout -P wwwdocs