我的學習之旅(24)system.h

system.h主要定義一些常用的x86彙編宏和字節序的處理。大部分都是拷貝linux中源代碼.

system.h源代碼:

#ifndef __SYSTEM_H__

#define __SYSTEM_H__

#ifndef NULL
#define NULL 0
#endif

typedef unsigned short u16;
typedef unsigned char u8;
typedef unsigned int u32;
typedef short s16;
typedef char s8;
typedef int s32;
typedef u32 dma_addr_t;

static inline unsigned int ntohl(unsigned int v)
{
    return  ( (( ( v ) & 0xff) << 24) |(( ( v >> 8 ) & 0xff) << 16) | ( ( ( v >> 16) & 0xff) << 8) | ( ( v >> 24) & 0xff) );
}

static inline unsigned short ntohs(unsigned short v)
{
    return ((((v) & 0xff)<<8) |(((v) >> 8) & 0xff));
}

#define htonl   ntohl
#define htons  ntohs


#define wmb() __asm__ __volatile__ ("": : :"memory")
#define X86_FEATURE_XMM2 (0*32+26)
#define alternative(oldinstr, newinstr, feature)   \
 asm volatile ("661:\n\t" oldinstr "\n662:\n"    \
        ".section .altinstructions,\"a\"\n"  \
        "  .align 4\n"     \
        "  .long 661b\n"            /* label */  \
        "  .long 663f\n"    /* new instruction */ \
        "  .byte %c0\n"             /* feature bit */ \
        "  .byte 662b-661b\n"       /* sourcelen */ \
        "  .byte 664f-663f\n"       /* replacementlen */ \
        ".previous\n"     \
        ".section .altinstr_replacement,\"ax\"\n"  \
        "663:\n\t" newinstr "\n664:\n"   /* replacement */\
        ".previous" :: "i" (feature) : "memory")
#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)