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diff --git a/Build/source/README.6cross b/Build/source/README.6cross new file mode 100644 index 00000000000..8527564f7f2 --- /dev/null +++ b/Build/source/README.6cross @@ -0,0 +1,105 @@ +(This file was generated by makeinfo and splitinfo.gawk.) +(Released under the old-style GNU documentation license; + see sources or other output files for full text.) + +8 Cross compilation +******************* + +In a cross compilation a "build" system is used to create binaries to be +executed on a "host" system with different hardware and/or operating +system. + + In simple cases, the build system can execute binaries for the host +system. This typically occurs for bi-arch systems where, e.g., +'i386-linux' binaries can run on 'x86_64-linux' systems and 'win32' +binaries can run on 'win64' systems. Although sometimes called "native +cross", technically this is not cross compilation at all. In most such +cases it suffices to specify suitable compiler flags. It might be +useful to add the configure option '--build=HOST' to get the correct +canonical host name, but note that this should _not_ be '--host=HOST' +(*note (autoconf)Hosts and Cross-Compilation::). + + In order to build, e.g., 32-bit binaries with 'clang' on a 64-bit OSX +system one could use + './Build --build=i386-apple-darwin CC='clang -arch i386'' \ + 'CXX='clang++ -arch i386' OBJCXX='clang++ -arch i386'' + +8.1 Cross configuring +===================== + +In a standard cross compilation, binaries for the host system cannot +execute on the build system and it is necessary to specify the configure +options '--host=HOST' and '--build=BUILD' with two different values. + + Building binaries requires suitable "cross" tools, e.g., compiler, +linker, and archiver, and perhaps a "cross" version of 'pkg-config' and +similar to locate host system libraries. Autoconf expects that these +cross tools are given by their usual variables or found under their +usual name prefixed with 'HOST-'. Here a list of such tools and +corresponding variables: + + ar AR + freetype-config FT2_CONFIG + g++ CXX + gcc CC + icu-config ICU_CONFIG + objdump OBJDUMP + pkg-config PKG_CONFIG + ranlib RANLIB + strip STRIP + +In order to, e.g., build 'mingw32' binaries on 'x86_64-linux' with a +cross compiler found as 'i386-pc-mingw32-gcc' one would specify + + --host=i386-pc-mingw32 --build=x86_64-linux-gnu + +or perhaps + + --host=mingw32 --build=x86_64-linux CC=i386-pc-mingw32-gcc + +but this latter, especially, might require adding 'CXX' and others. + + Configure arguments such as 'CFLAGS=...' refer to the cross compiler. +If necessary, you can specify compilers and flags for the few auxiliary +C and C++ programs required for the build process as configure arguments + + BUILDCC=... + BUILDCPPFLAGS=... + BUILDCFLAGS=... + BUILDCXX=... + BUILDCXXFLAGS=... + BUILDLDFLAGS=... + +8.2 Cross problems +================== + +The fact that binaries for the host system cannot be executed on the +build system causes some problems. + + One problem is that configure tests using 'AC_RUN_IFELSE' can compile +and link the test program but cannot execute it. Such tests should be +avoided if possible and otherwise must supply a pessimistic test result. + + Another problem arises if the build process must execute some +(auxiliary or installable) programs. Auxiliary programs can be placed +into a subdirectory that is configured natively as is done for +'texk/web2c/web2c', 'texk/dvipsk/squeeze', and 'texk/xdvik/squeeze'. +The module 'libs/freetype' uses the value of 'CC_BUILD', 'BUILD-gcc', +'gcc', or 'cc' as compiler for the auxiliary program. + + The situation for installable programs needed by the build process is +somewhat different. A quite expensive possibility, chosen for the ICU +libraries in module 'libs/icu', is to first compile natively for the +build system and in a second step to use these (uninstalled) programs +during the cross compilation. + + This approach would also be possible for the tools such as 'tangle' +used in the module 'texk/web2c' to build the WEB programs, but that +would require first building a native 'kpathsea' library. To avoid this +complication, cross compilation of the WEB or CWEB programs requires +sufficiently recent installed versions of 'tangle', 'ctangle', +'otangle', and 'tie'. + + Building 'xindy' requires running the host system 'clisp' binary, +thus cross compilation is not possible. + |