linux devmem 開發工具

  在Linux開發中着實用到的調試工具並不是很多。devmem的方式是提供給驅動開發人員，在應用層能夠偵測內存地址中的數據變化，以此來檢測驅動中對內存或者相關配置的正確性驗證。

        devmem2使用方法：

        devmem2 { address } [ type [ data ] ]

                address : 物理地址

                type :要訪問的數據類型 : [b]yte, [h]alfword, [w]ord

                data :想要寫入的數據，若爲讀取操作則省略此參數，若爲寫入，則必須含有此參數。

        如下就貼出devmem2的源代碼一探究竟。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/mman.h>

#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)

#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)

int main(int argc, char **argv) {
    int fd;
    void *map_base, *virt_addr;
    unsigned long read_result, writeval;
    off_t target;
    int access_type = 'w';

    if(argc < 2) {//若參數個數少於兩個則打印此工具的使用方法
        fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
            "\taddress : memory address to act upon\n"
            "\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
            "\tdata    : data to be written\n\n",
            argv[0]);
        exit(1);
    }
    target = strtoul(argv[1], 0, 0);

    if(argc > 2)
        access_type = tolower(argv[2][0]);


    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    printf("/dev/mem opened.\n");
    fflush(stdout);

    /* Map one page */ //將內核空間映射到用戶空間
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
    if(map_base == (void *) -1) FATAL;
    printf("Memory mapped at address %p.\n", map_base);
    fflush(stdout);

    virt_addr = map_base + (target & MAP_MASK);
    //針對不同的參數獲取不同類型內存數據
    switch(access_type) {
        case 'b':
            read_result = *((unsigned char *) virt_addr);
            break;
        case 'h':
            read_result = *((unsigned short *) virt_addr);
            break;
        case 'w':
            read_result = *((unsigned long *) virt_addr);
            break;
        default:
            fprintf(stderr, "Illegal data type '%c'.\n", access_type);
            exit(2);
    }
    printf("Value at address 0x%X (%p): 0x%X\n", target, virt_addr, read_result);
    fflush(stdout);
        //若參數大於3個，則說明爲寫入操作，針對不同參數寫入不同類型的數據
    if(argc > 3) {
        writeval = strtoul(argv[3], 0, 0);
        switch(access_type) {
            case 'b':
                *((unsigned char *) virt_addr) = writeval;
                read_result = *((unsigned char *) virt_addr);
                break;
            case 'h':
                *((unsigned short *) virt_addr) = writeval;
                read_result = *((unsigned short *) virt_addr);
                break;
            case 'w':
                *((unsigned long *) virt_addr) = writeval;
                read_result = *((unsigned long *) virt_addr);
                break;
        }
        printf("Written 0x%X; readback 0x%X\n", writeval, read_result);
        fflush(stdout);
    }

    if(munmap(map_base, MAP_SIZE) == -1) FATAL;
    close(fd);
    return 0;
}