8.5 Multi-architecture support

A number of platforms can execute code for more than one architecture. For example, 64-bit platforms such as AMD64, MIPS64, Sparc64, and PowerPC64 support the execution of both 32-bit and 64-bit code. Similarly, ARM processors support both ARM code and a more compact code called "Thumb". GCC can be built to support multiple architectures on these platforms. By default, the compiler will generate 64-bit object files, but giving the -m32 option will generate a 32-bit object file for the corresponding architecture.⁽²⁵⁾

Note that support for multiple architectures depends on the corresponding libraries being available. On 64-bit platforms supporting both 64 and 32-bit executables, the 64-bit libraries are often placed in 'lib64' directories instead of 'lib' directories, e.g. in '/usr/lib64' and '/lib64'. The 32-bit libraries are then found in the default 'lib' directories as on other platforms. This allows both a 32-bit and a 64-bit library with the same name to exist on the same system. Other systems, such as the IA64/Itanium, use the directories '/usr/lib' and '/lib' for 64-bit libraries. GCC knows about these paths and uses the appropriate path when compiling 64-bit or 32-bit code.