私の投稿を更新しました...
私はプログラムの下に着きました。とで動作し/dev/kmemます/dev/mem。
コードから何かを学ぶことができると思います。しかし、Beagle Boardで実行すると、以下の結果が得られます。
case 1: ( if(1) )
root@omap:/home/ubuntu/tom# ./kmem_mem /boot/System.map-3.0.4-x3
found jiffies at (0xc0870080) c0870080
/dev/kmem read buf = 319317
jiffies=319317 (read from virtual memory)
/dev/mem: the offset is 870080
the page size = 4096
mmap: Invalid argument
case 2: ( if(0) )
root@omap:/home/ubuntu/tom# ./kmem_mem /boot/System.map-3.0.4-x3
found jiffies at (0xc0870080) c0870080
/dev/kmem read buf = 333631
jiffies=333631 (read from virtual memory)
/dev/mem: the offset is 870080
/dev/mem read failed: Bad address
jiffies=0 (read from physical memory)
そして、mmapが最初のパラメーターとしてNULLを使用できるように、以下のコマンドを使用しました。
root@omap:/home/ubuntu/tom# echo 0 > /proc/sys/vm/mmap_min_addr
root@omap:/home/ubuntu/tom# cat /proc/sys/vm/mmap_min_addr
0
ご覧のとおり、正常にread_kmem()動作しますがread_mem()動作せず、転送された「オフセット」が間違っているようです。しかし、カーネルアドレス- PAGE_OFFSET(0xC0000000) = physical address、それは間違っていますか？
私の質問は次のとおりです。（1）ケース1の「mmap：無効な引数」はなぜですか？（2）mmapがPAGE_SIZE長さ空間のみをマップするのはなぜですか？（3）何が問題になっていread_memますか？
誰か助けてもらえますか？ありがとう！
/*
* getjiff.c
*
* this toolkit shows how to get jiffies value from user space:
* 1. find jiffies's address from kernel image.
* 2. access virtual address space to get jiffies value.
* 3. access physical address sapce to get jiffies value.
*
* demostrate following techniques:
* o get ELF object symbol address by calling nlist()
* o access virtual memory space from /dev/kmem
* o access virtual memory space from /dev/mem
*/
#include <stdio.h>
#include <stdlib.h> //exit
#include <linux/a.out.h> //nlist
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <memory.h>
#define LONG *(volatile unsigned long*)
/* read from virtual memory */
int read_kmem(off_t offset, void* buf, size_t count)
{
int fd;
int n;
fd = open("/dev/kmem", O_RDONLY);
if (fd < 0)
{
perror("open /dev/kmem failed");
return -1;
}
lseek(fd, offset, SEEK_SET);
n = read(fd, buf, count);
if (n != count)
perror("/dev/kmem read failed");
else
printf("/dev/kmem read buf = %ld\n", *(unsigned long *)buf);
close(fd);
return n;
}
/* read from physical memory */
int read_mem(off_t offset, void* buf, size_t count)
{
int fd;
int n;
int page_size;
void *map_base;
unsigned long value;
printf("/dev/mem: the offset is %lx\n", offset);
fd = open("/dev/mem", O_RDONLY);
if (fd < 0)
{
perror("open /dev/mem failed");
return -1;
}
if(1){
page_size = getpagesize();
printf("the page size = %d\n", page_size);
map_base = mmap(0,page_size,PROT_READ,MAP_SHARED,fd,offset);
if (map_base == MAP_FAILED){
perror("mmap");
exit(1);
}
value = LONG(map_base);
printf("/dev/mem: the value is %ld\n", value);
buf = (unsigned long *)map_base;
}
if(0){
lseek(fd, offset, SEEK_SET);
n = read(fd, buf, count);
if (n != count)
perror("/dev/mem read failed");
else
printf("/dev/mem read buf = %ld\n", *(unsigned long *)buf);
}
close(fd);
return n;
}
int main(int argc, char **argv)
{
FILE *fp;
char addr_str[11]="0x";
char var[51];
unsigned long addr;
unsigned long jiffies;
char ch;
int r;
if (argc != 2) {
fprintf(stderr,"usage: %s System.map\n",argv[0]);
exit(-1);
}
if ((fp = fopen(argv[1],"r")) == NULL) {
perror("fopen");
exit(-1);
}
do {
r = fscanf(fp,"%8s %c %50s\n",&addr_str[2],&ch,var); // format of System.map
if (strcmp(var,"jiffies")==0)
break;
} while(r > 0);
if (r < 0) {
printf("could not find jiffies\n");
exit(-1);
}
addr = strtoul(addr_str,NULL,16); //Convert string to unsigned long integer
printf("found jiffies at (%s) %08lx\n",addr_str,addr);
read_kmem(addr, &jiffies, sizeof(jiffies));
printf("jiffies=%ld (read from virtual memory)\n\n", jiffies);
jiffies = 0; //reinit for checking read_mem() below
read_mem(addr-0xC0000000, &jiffies, sizeof(jiffies));
printf("jiffies=%ld (read from physical memory)\n", jiffies);
return 0;
}