https://blog.csdn.net/xy010902100449/article/details/47028497
【摘要】 在Linux开发中着实用到的调试工具并不是很多。devmem的方式是提供给驱动开发人员,在应用层能够侦测内存地址中的数据变化,以此来检测驱动中对内存或者相关配置的正确性验证。
http://blog.csdn.net/hens007/article/details/7268447
这个工具的原理也比较简单,就是应用程序通过mmap函数实现对/dev/mem驱动中mmap方法的使用,映射了设备的内存到用户空间,实现对这些物理地址的读写操作。
#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]
",
__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) {//若参数个数少于两个则打印此工具的使用方法
fprintf(stderr, "
Usage: %s { address } [ type [ data ] ]
"
" address : memory address to act upon
"
" type : access operation type : [b]yte, [h]alfword, [w]ord
"
" data : data to be written
",
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.
");
fflush(stdout);
/* Map one page */ //将内核空间映射到用户空间
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.
", map_base);
fflush(stdout);
virt_addr = map_base + (target & MAP_MASK);
//针对不同的参数获取不同类型内存数据
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'.
", access_type);
exit(2);
}
printf("Value at address 0x%X (%p): 0x%X
", target, virt_addr, read_result);
fflush(stdout);
//若参数大于3个,则说明为写入操作,针对不同参数写入不同类型的数据
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
", writeval, read_result);
fflush(stdout);
}
if(munmap(map_base, MAP_SIZE) == -1) FATAL;
close(fd);
return 0;
}
memdev:直接读写内存。
可以在busybox的杂项中找到:
CONFIG_USER_BUSYBOX_DEVMEM:
devmem is a small program that reads and writes from physical
memory using /dev/mem.
Symbol: USER_BUSYBOX_DEVMEM [=y]
Prompt: devmem
Defined at ../user/busybox/busybox-1.14.3/miscutils/Kconfig:216
Depends on: USER_BUSYBOX_BUSYBOX
Location:
-> BusyBox (USER_BUSYBOX_BUSYBOX [=y])
-> Miscellaneous Utilities
[用法]
Usage: devmem ADDRESS [WIDTH [VALUE]]
读取:在地址0x97000000读取32bit值(WIDTH默认等于32, 可选值为[8, 16, 32, 64])
/dev # devmem 0x97000000
0x11111111
读取:在地址0x97000000读取16bit值
/dev # devmem 0x97000000 16
0x1111
写入:在地址0x97000000写入32bit值0x7777ABCD
/dev # devmem 0x97000000 32 0x7777ABCD
/dev # devmem 0x97000000
0x7777ABCD
注意:如果/dev下没有mem这个node,会出现错误:
/dev # devmem 0x97000000
devmem: can't open '/dev/mem': No such file or directory
这时可以在Host系统中手动创建一个(例如在NFS root filesystem模式):
host@host-laptop:~/embedded/tftpboot/nfsroot/dev$ sudo mknod mem -m666 c 1 1
注意这里的权限是666,允许任何人任意读写,可以很好的配合程序debug。
/dev # devmem 0x97000000
0x7777ABCD
---------------------
作者:狂奔的乌龟
来源:CSDN
原文:https://blog.csdn.net/xy010902100449/article/details/47028497
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