GCC: sorry, unimplemented: 64-bit mode not compiled in

Question

I have built GCC 4.7 on my x86 32-bit linux system. When I try to cross-compile with the -m64 flag I get the following:

sorry, unimplemented: 64-bit mode not compiled in

while the compiler provided by default by my Linux distribution can cross-compile with -m64.

What do I have to pass to ./configure to enable the 64bit mode in GCC? These are the options I used to build GCC 4.7:

$ /usr/local/bin/g++ -v Using built-in specs.
COLLECT_GCC=/usr/local/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/i686-pc-linux-gnu/4.7.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ./configure --enable-multiarch --with-cloog=/usr/local/ --with-mpfr=/usr/local/ --with-ppl=/usr/local/ --verbose --enable-languages=c,c++
Thread model: posix gcc version 4.7.0 20120113 (experimental) (GCC)

EDIT:

--enable-multilib and --enable-targets=i686-pc-linux-gnu,x86_64-pc-linux-gnu

do not change the situation. The compiler still complains about 64 bit mode not compiled in:

$ g++ -v Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/i686-pc-linux-gnu/4.7.0/lto-wrapper Target: i686-pc-linux-gnu Configured with: ./configure --enable-multiarch --with-cloog=/usr/local/ --with-mpfr=/usr/local/ --with-ppl=/usr/local/ --verbose --enable-languages=c,c++ --enable-multilib --enable-targets=i686-pc-linux-gnu,x86_64-pc-linux-gnu Thread model: posix gcc version 4.7.0 20120113 (experimental) (GCC)

$ g++ -m64 c.cpp c.cpp:1:0: sorry, unimplemented: 64-bit mode not compiled in

Answer 1

This typically means that you're using the wrong (old) compiler.

The new compilers support both -m32 and -m64. You have to set the PATH to the new compilers (in the gcc,MinGW subdirectory of Rtools) before any old compilers in Rtools.

Try updating your compiler's binary lib path to 64bit version. Other resources like lib folders also should change accordingly.

Answer 2

You will need both binutils and gcc configured with:

--enable-multilib

and probably:

--enable-targets=i686-pc-linux-gnu,x86_64-pc-linux-gnu

to support multilib (the -m64 and/or -m32 options). You'll also need two versions of stuff like glibc to be able to link and run the resulting binaries.