1. 根目录:
2. include
3. uapi
4. asm-generic
5. bitsperlong.h

#ifndef _UAPI__ASM_GENERIC_BITS_PER_LONG
#define _UAPI__ASM_GENERIC_BITS_PER_LONG

/*
 * There seems to be no way of detecting this automatically from user
 * space, so 64 bit architectures should override this in their
 * bitsperlong.h. In particular, an architecture that supports
 * both 32 and 64 bit user space must not rely on CONFIG_64BIT
 * to decide it, but rather check a compiler provided macro.
 */
#ifndef __BITS_PER_LONG
#define __BITS_PER_LONG 32
#endif

#endif /* _UAPI__ASM_GENERIC_BITS_PER_LONG */