Re: Initial cross-compilation support

[Nikita Karetnikov <nikita@karetnikov.org>]

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I was able to cross-compile a "hello world" program.

First, I created the following symlinks:

# ln -s /nix/store/mifp2p1zjlvb4ndslw1r8grkpglybqjf-glibc-cross-mips64el-linux-gnu-2.17/lib/crti.o /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/crti.o
# ln -s /nix/store/mifp2p1zjlvb4ndslw1r8grkpglybqjf-glibc-cross-mips64el-linux-gnu-2.17/lib/crt1.o /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/crt1.o
# ln -s /nix/store/mifp2p1zjlvb4ndslw1r8grkpglybqjf-glibc-cross-mips64el-linux-gnu-2.17/lib/crtn.o /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/crtn.o

These are needed because I haven't found a way to set the
CROSS_LIBRARY_PATH variable.  (I'll show an example below.)

Then I set this variable:

# export COMPILER_PATH=/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/libexec/gcc/mips64el-linux-gnu:/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/libexec/gcc/mips64el-linux-gnu/4.7.2

which is used to locate subprograms [1].

After that I specified this one:

# export C_INCLUDE_PATH=/nix/store/mifp2p1zjlvb4ndslw1r8grkpglybqjf-glibc-cross-mips64el-linux-gnu-2.17/include

And compiled the following program:

#include <stdio.h>

int main ()
{
  printf ("Hello World!\n");
}

# /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/bin/mips64el-linux-gnu-gcc -static -o hello hello.c

Then I ran 'hello' on mips64el and it worked.  Is it enough to be sure
that cross-compiler will also work for non-trivial programs?

Here is the example I mentioned:

# export CROSS_LIBRARY_PATH=foo
# /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/bin/mips64el-linux-gnu-gcc -static -o hello -v hello.c |& grep CROSS_LIBRARY_PATH
CROSS_LIBRARY_PATH=/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/:/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/../../../../mips64el-linux-gnu/lib

Note that CROSS_LIBRARY_PATH is not set to 'foo'.  Could you explain
why?  Is it determined automatically (e.g., based on the location of
GCC)?

# ltrace /nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/bin/mips64el-linux-gnu-gcc -static -o hello -v hello.c |& grep CROSS_LIBRARY_PATH
getenv("CROSS_LIBRARY_PATH")                     = "foo"
strlen("CROSS_LIBRARY_PATH")                     = 18
memcpy(0x0867b044, "CROSS_LIBRARY_PATH", 18)     = 0x0867b044
vfprintf(0xb77b3980, "%s\n", 0xbf9b3d88CROSS_LIBRARY_PATH=/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/:/nix/store/khdyz3i5aih56lxfk6hjvp3884apm7qb-gcc-cross-mips64el-linux-gnu-4.7.2/lib/gcc/mips64el-linux-gnu/4.7.2/../../../../mips64el-linux-gnu/lib/
putenv("CROSS_LIBRARY_PATH=/nix/store/kh"...)    = 0

How did 'vfprintf' get its third argument?

Comments?  Do you know how to do it without the symlinks?

[1] http://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html

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