[Bug driver/87769] GCC build from source uses headers and libraries from directories host machine.

[mte.zych at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87769

--- Comment #4 from Mateusz Zych <mte.zych at gmail dot com> ---
Right, the "--with-sysroot=" configuration parameter is the key.
The sysroot directory defines minimal filesystem of a target machine,
in particular it should contain standard C library and Linux kernel headers,
so it makes sense that I have to provide the sysroot directory
to build standalone GCC, which would be a cross compiler.

However, I don't understand why would
configuration parameters "--host=" and "--target=",
define whether I am building a cross compiler or not.
To me, what differentiates cross compiler form native compiler,
is the location of libraries and headers.

 - Native compilers use libraries and headers from host machine.
 - Cross compilers never touch host machine and always use sysroot.

Of course, all compilers targeting different architecture compared to
architecture of the host machine have be cross compilers.
But the opposite is not true - not all cross compilers have to target
architecture different from architecture of the host machine.
They can match, no problem!
And this is exactly what I'm trying to do - I want build GCC cross compiler
targeting the exact same architecture that my host machine is using.


OK, with that out of the way, I've updated my script:

    # Linux
    wget https://kernel.org/pub/linux/kernel/v4.x/linux-4.19.tar.gz
    tar -xvf linux-4.19.tar.gz
    mv linux-4.19 linux-source
    cd linux-source
    make ARCH=x86_64 INSTALL_HDR_PATH=$PWD/../gcc/sysroot/usr headers_install
    cd ..

    # GNU C Library (glibc)
    wget https://ftp.gnu.org/gnu/glibc/glibc-2.28.tar.gz
    tar -xvf glibc-2.28.tar.gz
    mv glibc-2.28 glibc-source
    mkdir glibc-build
    cd glibc-build
    ../glibc-source/configure --build=x86_64-linux-gnu \
                              --host=x86_64-linux-gnu \
                              --target=x86_64-linux-gnu \
                              --prefix=$PWD/../gcc/sysroot/usr \
                              --with-headers=$PWD/../gcc/sysroot/usr/include \
                              --disable-multilib \
                              --disable-nls \
                              --disable-timezone-tools
    make all -j 4
    make install
    cd ..

    # GNU Binutils
    wget https://ftp.gnu.org/gnu/binutils/binutils-2.31.tar.gz
    tar -xvf binutils-2.31.tar.gz
    mv binutils-2.31 binutils-source
    mkdir binutils-build
    cd binutils-build
    ../binutils-source/configure --build=x86_64-linux-gnu \
                                 --host=x86_64-linux-gnu \
                                 --target=x86_64-linux-gnu \
                                 --prefix=$PWD/../gcc \
                                 --with-sysroot=$PWD/../gcc/sysroot \
                                 --disable-multilib \
                                 --disable-nls
    make all -j 4
    make install
    cd ..

    # GCC
    wget https://ftp.gnu.org/gnu/gcc/gcc-8.2.0/gcc-8.2.0.tar.gz
    tar -xvf gcc-8.2.0.tar.gz
    mv gcc-8.2.0 gcc-source
    cd gcc-source
    ./contrib/download_prerequisites
    cd ..
    mkdir gcc-build
    cd gcc-build
    ../gcc-source/configure --build=x86_64-linux-gnu \
                            --host=x86_64-linux-gnu \
                            --target=x86_64-linux-gnu \
                            --prefix=$PWD/../gcc \
                            --with-sysroot=$PWD/../gcc/sysroot \
                            --enable-languages=c,c++ \
                            --disable-multilib \
                            --disable-nls
    make all -j 4
    make install
    cd ..

Essentially I am puting:
 - GCC and Binutils into $ROOT/gcc and
 - glibc with Linux headers into ROOT/gcc/sysroot.


Unfortunately with updated script, GCC is not compiling anymore. :(
I've never managed to compile GCC configured with parameter "--with-sysroot=".

What is actually failing? Well, the libgcc_s.so fails to link with libc.so.6:

    attempt to open
/home/mzych/standalone-gcc/gcc-build/../gcc/sysroot/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/libc.so.6
failed
    attempt to open
/home/mzych/standalone-gcc/gcc-build/../gcc/sysroot/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/libc_nonshared.a
failed
    attempt to open
/home/mzych/standalone-gcc/gcc-build/../gcc/sysroot/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/ld-linux-x86-64.so.2
failed

    /usr/bin/ld: cannot find
/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/libc.so.6        
   inside /home/mzych/standalone-gcc/gcc-build/../gcc/sysroot
    /usr/bin/ld: cannot find
/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/libc_nonshared.a 
   inside /home/mzych/standalone-gcc/gcc-build/../gcc/sysroot
    /usr/bin/ld: cannot find
/home/mzych/standalone-gcc/glibc-build/../gcc/sysroot/usr/lib/ld-linux-x86-64.so.2
inside /home/mzych/standalone-gcc/gcc-build/../gcc/sysroot

To me this failure looks like an issue with sysroot path,
because the sysroot path is appended twice.


I would be very grateful if somebdy could help me understand
how to build GCC using "--with-sysroot=" configuration option.


Thank you, Mateusz