Henri, Et al... On Thu, Oct 8, 2015 at 6:23 PM, Henri Tuhola <henri.tuhola@xxxxxxxxx> wrote: > Hi GCC maintainers [disclaimer: I don't speak as an official gnu/gcc developer/maintainer, as I am not.] > I've spent few days trying to figure out how to build a cross compiler > for my linux distribution. I've found plenty of instructions but only > the unsatisfying instructions have been worked. > > The particular instructions that work are located at the "cross linux > from scratch" -tutorial: > http://www.clfs.org/view/CLFS-3.0.0-SYSTEMD/x86_64-64/cross-tools/chapter.html > > The problem with these tutorials are that they propose to patch the > gcc/config -directory and build files to get the library compile > correct. I wrote my current build scripts based on them and got it to > work. The problem is that I cannot trust that they keep working on. > > I thought for a moment that I had found good instructions at > http://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/ but > neither these worked out. > > So consider that you're starting out a distribution. What is the > preferred way of compiling a cross-compiler and then the compiler for > your platform? The biggest concern seems to be that the paths > > Here's a sample of what kind of crazy the clfs scripts consist of, > after they've patched the gcc/config and replaced every /lib(64)? > -pattern with /tools/lib In the LFS example, there is a "bootstrap" process that is different then a native compiler build of gcc. In that process, a temporary set of libraries and tools that are requirements for the final system are put in the /tools and /cross-tools directories. This next command was and is specific to LFS (regardless of what LELUX is...): > AR=ar LDFLAGS="-Wl,-rpath,/cross-tools/lib" \ > $GCC_SOURCES/configure --prefix=/cross-tools \ > --build=${LELUX_HOST} --host=${LELUX_HOST} --target=${LELUX_TARGET} \ > --with-sysroot=${LELUX} --with-local-prefix=/tools \ > --with-native-system-header-dir=/tools/include \ > --disable-nls --disable-shared \ > --with-mpfr=/cross-tools \ > --with-gmp=/cross-tools \ > --with-mpc=/cross-tools \ > --without-headers --with-newlib --disable-decimal-float > --disable-libgomp \ > --disable-libmudflap --disable-libssp --disable-libatomic > --disable-libitm \ > --disable-libsanitizer --disable-libquadmath --disable-threads \ > --disable-multilib --disable-target-zlib --with-system-zlib \ > --enable-languages=c --enable-checking=release > make -j4 all-gcc all-target-libgcc > make install-gcc install-target-libgcc > > I feel this is important, as there's many other people constructing > cross compiler tools. Actually I just looked in how gcw0 toolchain has > been configured: Where as this one is built in a different environment (probably exporting CFLAGS, LDFLAGS, etc... outside of the ./configure command): > Configured with: ./configure --prefix=/opt/gcw0-toolchain/usr > --sysconfdir=/opt/gcw0-toolchain/etc --enable-shared --enable-static > --target=mipsel-gcw0-linux-uclibc > --with-sysroot=/opt/gcw0-toolchain/usr/mipsel-gcw0-linux-uclibc/sysroot > --disable-__cxa_atexit --with-gnu-ld --disable-libssp > --disable-multilib --with-gmp=/opt/gcw0-toolchain/usr > --with-mpfr=/opt/gcw0-toolchain/usr --enable-target-optspace > --disable-libsanitizer --enable-tls --disable-libmudflap > --enable-threads --with-mpc=/opt/gcw0-toolchain/usr > --disable-decimal-float --with-arch=mips32r2 --with-tune=mips32r2 > --with-abi=32 --with-pkgversion='Buildroot 2014.05-gbb847d4' > --with-bugurl=http://bugs.buildroot.net/ --enable-languages=c,c++ > --with-build-time-tools=/opt/gcw0-toolchain/usr/mipsel-gcw0-linux-uclibc/bin > --disable-libgomp --enable-lto > > Doesn't seem that different. It is. AFAIU, there is a build arch [the architecture the compiler is built on], a host arch [the architecture the compiler runs on], and the target arch [the architecture the compiler produces binaries for]. <shameless-plug> You could check out http://crosstool-ng.org and https://github.com/crosstool-ng/crosstool-ng </shameless-plug> Again, AFAIU, gcc has the ability to be configured in four different ways: The Native Compiler: x86_64 (build), x86_64 (host), x86_64 (target) [not yet in ct-ng] (may be in a different --prefix the the one provided by the distribution, or maybe the one provided by the distribution) Cross-Compiler: x86_64 (build), x86_64 (host), armel (target) [default in ct-ng] (almost always in a different --prefix, and preferably relocatable - filesystem wise) Cross-Native: x86_64 (build), Sparc (host), x86_64 (target) [not yet in ct-ng] (same as cross-compiler) Cross-Canadian: x86_64 (build), Sparc (host), aarch64 (target) [optional in ct-ng] (same as cross-compiler) GCC is a contributor supported project, much like any other open-source software project; there is always on-going work to improve the process of building gcc, as well as adding new features and target architectures. Help wanted! :) There are always exceptions to the process of building any variant of the above examples where changes need to be back-ported from newer versions of gcc [possibly development versions] (such as say, fixes to gccgo, different/new or experimental LIBCs, or being able to specify different library paths for the cross-compiler's architecture specific libraries/headers - as simple examples) [see also Yocto-project/OpenEmbedded, rhel, debian, buildroot, crosstool-ng, openwrt, etc...], or different dependencies on external libraries (such as gmp, mpfr, isl, libbfd, etc...) or whether it is targeted for a specific operating system or bare-metal. Crosstool-NG, Buildroot, LFS, Yocto/OpenEmbedded, rhel, debian, arch-linux, embedded systems on bare-metal, etc... (at one time Apple) all mangle with the black-art of building a gcc cross-compiler, specific for the purpose of the target architecture-vendor-operatingsystem-libc (tuple) and goal of the distribution (I.E.: security hardened or compatibility or embedded niche, etc...). It is not a simple: one command-line to build a cross-compiler for any architecture kind of thing... Which is probably the thing that has you confused. As rightfully, everything should be reproducible, in a consistent way. Cross-Compilers are just not that way. Some architectures require different settings and possibly options of gcc or required libraries to be enabled or disabled to produce the desired effect. Cheers, -Bryan "Oh no, I've said too much I haven't said enough" -- REM
