在Linux的应用态程序中，如何access 系统的physical memory呢？此时，就要用上/dev/mem了。

Introduction

利用/dev/mem，通过mmap可以将物理地址映射到用户空间的虚拟地址上，从而可以access physical memory。

Example code

Access physical memory from Linux user space

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int mem_dev = open("/dev/mem", O_RDWR | O_SYNC);

const uint32_t mem_address = 0x10001234
const uint32_t mem_size = 0x100;

uint32_t alloc_mem_size, page_mask, page_size;
void *mem_pointer, *virt_addr;

page_size = sysconf(_SC_PAGESIZE);
alloc_mem_size = (((mem_size / page_size) + 1) * page_size);
page_mask = (page_size - 1);

mem_pointer = mmap(NULL,
                   alloc_mem_size,
                   PROT_READ | PROT_WRITE,
                   MAP_SHARED,
                   mem_dev,
                   (mem_address & ~page_mask)
                   );

if(mem_pointer == MAP_FAILED)
{  
      // Error
}

virt_addr = (mem_pointer + (mem_address & page_mask));

At the end of this code, if no errors occurred, you have a pointer virt_addr to the physical memory space from address 0x10001234 to 0x10001334. You can use this pointer in read/write mode but be very carefully since an incorrect modify to some critical memory section will crash the system.

参考资料：

  1. Access physical memory from Linux user space
  2. /dev/mem可没那么简单