摘要：
这是一个可以访问应用层中底层寄存器的应用程序源代码。第40行添加了O_ DSYNC标志，以防止由于缓存=5）｛21printf；22printf、23printf，24printf和25return-1；26｝2728，如果｛29flag=0；30value=strtol；31｝32else｛33flag=1；34value=strstol；35｝3637base=strto；38addr=结构；3940dev_ fd=打开；4142if43｛44printf；45return0；46｝4748addr&=~0x3；49align_ addr=地址&~0xff；5051map_大小=地址+0x100；52打印f；53map_ base=mmap；54if55｛56printf；57错误；58返回-1；59｝6061如果｛6263表示｛64if｛65printf（“”）；66打印f；67｝68打印f；69}70printf（“”）；7172｝73否则｛74printf；75*=值；76｝77printf（“”）；7879if80关闭；8182munmap；8384返回0；85}3.内核设备文件实现内核源代码位置：/drivers/char/mem C/dev/mem设备文件mmap函数实现：静态int mmap_mem｛size_tsize=vma-˃vm_end-vma-˃vm_start；phys_addr_tofset=vma-˃vm_pgoff˂˂PAGE_SHIFT！
1.程序说明：
调试驱动程序时，经常遇到候需要查看或设置寄存器的情况，但是直接更改内核代码又不方便。
这里提供一个应用程序源码能在应用层访问底层寄存器。（网上找到的，进行过更改）。
这里只提供4字节数据的访问，如果需要其他字节宽度则需要更改代码。
line40 增加了O_DSYNC标志，防止cache导致数据写入不及时。
2.应用程序源码
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <time.h>
4 #include <unistd.h>
5 #include <fcntl.h>
6 #include <unistd.h>
7 #include <stdint.h>
8 #include <sys/mman.h>
9 #include <errno.h>
10
11 static intdev_fd;
12 int main(int argc, char **argv)
13 {
14 uint32_t addr, value, map_size,base;
15 void *align_addr;
16 int flag = 0;
17 inti;
18 unsigned char *map_base;
19
20 if (argc != 5) {
21 printf("usage: m_reg r base address readcount
");
22 printf("example: m_reg r 0x50008000 20 1
");
23 printf("usage: m_reg w base address writevalue
");
24 printf("example: m_reg w 0x50008000 20 0xffffffff
");
25 return -1;
26 }
27
28 if (argv[1][0] == 'r') {
29 flag = 0;
30 value = strtol(argv[4], NULL, 10);
31 }
32 else{
33 flag = 1;
34 value = strtol(argv[4], NULL, 16);
35 }
36
37 base = strtol(argv[2], NULL, 16);
38 addr = strtol(argv[3], NULL, 16);
39
40 dev_fd = open("/dev/mem", O_RDWR | O_NDELAY |O_DSYNC);
41
42 if (dev_fd < 0)
43 {
44 printf("open(/dev/mem) failed.");
45 return 0;
46 }
47
48 addr &= ~0x3;
49 align_addr = addr & ~0xff;
50
51 map_size = addr + 0x100;
52 printf("map base:0x%x size:0x%x
",base,map_size);
53 map_base = (unsigned int * )mmap(NULL, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, dev_fd, base);
54 if(map_base == -1)
55 {
56 printf("map err %d
",errno);
57 perror("errno:");
58 return -1;
59 }
60
61 if (flag == 0) {
62
63 for (i = 0; i < value; i++) {
64 if (i % 4 == 0) {
65 printf("
");
66 printf("0x%08x ", addr+i*4);
67 }
68 printf("%08x ", *(volatile unsigned int *)(map_base+addr+i*4));
69 }
70 printf("
");
71
72 }
73 else{
74 printf("0x%08x value:0x%x", addr,value);
75 *(volatile unsigned int *)(map_base + addr) =value;
76 }
77 printf("
");
78
79 if(dev_fd)
80 close(dev_fd);
81
82 munmap((unsigned int *)map_base, map_size);
83
84 return 0;
85 }3. 内核设备文件实现
内核源码位置：/drivers/char/mem.c
/dev/mem设备文件mmap函数实现：
static int mmap_mem(struct file *file, struct vm_area_struct *vma)
{
size_t size = vma->vm_end - vma->vm_start;
phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
/* It's illegal to wrap around the end of the physical address space. */
if (offset + (phys_addr_t)size - 1 < offset)
return -EINVAL;
if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
return -EINVAL;
if (!private_mapping_ok(vma))
return -ENOSYS;
if (!range_is_allowed(vma->vm_pgoff, size))
return -EPERM;
if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
&vma->vm_page_prot))
return -EINVAL;
vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
size,
vma->vm_page_prot);
vma->vm_ops = &mmap_mem_ops;
/* Remap-pfn-range will mark the range VM_IO */
if (remap_pfn_range(vma,
vma->vm_start,
vma->vm_pgoff,
size,
vma->vm_page_prot)) {
return -EAGAIN;
}
return 0;
}
phys_mem_access_prot函数获得映射内存访问权限
static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
unsigned long size, pgprot_t vma_prot)
{
#ifdef pgprot_noncached
phys_addr_t offset = pfn << PAGE_SHIFT;
if (uncached_access(file, offset))
return pgprot_noncached(vma_prot);
#endif
return vma_prot;
}
O_DSYNC标志将会使用不带cache的映射方式，该标志在打开设备文件时指定。
static int uncached_access(struct file *file, phys_addr_t addr)
{
/*
* Accessing memory above the top the kernel knows about or through a
* file pointer
* that was marked O_DSYNC will be done non-cached.
*/
if (file->f_flags & O_DSYNC)
return 1;
return addr >= __pa(high_memory);
}