User guide

Running GCC

$ file hello64

hello64: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), dynamically linked

(uses shared libs), for GNU/Linux 2.6.18, not stripped

$ ldd hello64

linux-vdso.so.1 => (0x00007fff242dd000)

libc.so.6 => /lib64/libc.so.6 (0x00007f0721514000)

/lib64/ld-linux-x86-64.so.2 (0x00007f0721893000)

The command file on a 64-bit executable will include ELF 64-bit in its output, and ldd will

list /lib64/libc.so.6 as the main C library linked.

3. On a 64-bit system, compile hello.c into a 32-bit executable with:

gcc -m32 hello.c -o hello32

4. Ensure that the resulting executable is a 32-bit binary:

$ file hello32

hello32: ELF 32-bit LSB executable, Intel 80386, version 1 (GNU/Linux), dynamically

linked (uses shared libs), for GNU/Linux 2.6.18, not stripped

$ ldd hello32

linux-gate.so.1 => (0x007eb000)

libc.so.6 => /lib/libc.so.6 (0x00b13000)

/lib/ld-linux.so.2 (0x00cd7000)

The command file on a 32-bit executable will include ELF 32-bit in its output, and ldd will

list /lib/libc.so.6 as the main C library linked.

If you have not installed the 32-bit supporting libraries you will get an error similar to this for C code:

$ gcc -m32 hello32.c -o hello32

/usr/bin/ld: crt1.o: No such file: No such file or directory

collect2: ld returned 1 exit status

A similar error would be triggered on C++ code:

$ g++ -m32 hello32.cc -o hello32-c++

In file included from /usr/include/features.h:385,

from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/x86_64-redhat-

linux/32/bits/os_defines.h:39,

from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/x86_64-redhat-

linux/32/bits/c++config.h:243,

from /usr/lib/gcc/x86_64-redhat-linux/4.4.4/../../../../include/c++/4.4.4/iostream:39,

from hello32.cc:1:

/usr/include/gnu/stubs.h:7:27: error: gnu/stubs-32.h: No such file or directory

These errors indicate that the supporting 32-bit libraries have not been properly installed as explained

at the beginning of this section.

It is important to note that even if 32-bit binaries can run on 64-bit systems, it is preferrable to have

64-bit binaries unless otherwise needed. In order to run 32-bit binaries on 64-bit systems, the system

must import additional 32-bit shared libraries that must be loaded in tandem with the 64-bit libraries

(for example glibc). This causes additional memory usage on such systems. It is always preferrable to

have 64-bit binaries for 64-bit systems and 32-bit binaries for 32-bit systems.