arch/x86/Makefile

arch/x86/Makefile defines the variable BITS as «an extension for files which are available in a 32 and 64-bit version to simplify shared Makefiles».

The value of BITS is set to 32 if CONFIG_X86_32 set, otherwise, it is set to 64.

Examples of source files that come in two versions are

• arch/x86/boot/compressed/head_32.S and arch/x86/boot/compressed/head_64.S
• arch/x86/entry/entry_32.S and arch/x86/entry/entry_64.S

BITS is also used to set the compiler option -m32 or -m64.