如何释放使用mmap分配的内存?

时间:2021-08-15 00:42:51

I have allocated code using mmap, but unable to free it because of segmentation fault. I have done mprotect - PROT_WRITE to make it writable, but still i am unable to free it.

我已经使用mmap分配了代码,但由于分段错误而无法释放代码。我已经完成了mprotect - PROT_WRITE以使其可写,但我仍然无法释放它。

Please help me.

请帮我。

enter code here
 1 #include <stdio.h>
 2 #include <memory.h>
 3 #include <stdlib.h>
 4 #include <unistd.h>
 5 #include <sys/mman.h>
 6 #include <sys/types.h>
 7 #include <fcntl.h>
 8 
 9 int main()
10 {
11  void * allocation;
12  size_t size;
13  static int devZerofd = -1;
14 
15  if ( devZerofd == -1 ) {
16                 devZerofd = open("/dev/zero", O_RDWR);
17                 if ( devZerofd < 0 )
18                         perror("open() on /dev/zero failed");
19 }
20 
21  allocation = (caddr_t) mmap(0, 5000, PROT_READ|PROT_NONE, MAP_PRIVATE, devZerofd,  0);
22 
23  if ( allocation == (caddr_t)-1 )
24                 fprintf(stderr, "mmap() failed ");
25 
26  if ( mprotect((caddr_t)allocation, 5000, PROT_WRITE) < 0 )
27         fprintf(stderr, "mprotect failed");
28  else
29         printf("mprotect done: memory allocated at address %u\n",allocation);
30 
31  strcpy(allocation,"Hello, how are you");
32  puts(allocation);
33 
34  if ( mprotect((caddr_t)allocation, 5000, PROT_WRITE) < 0 )
35         fprintf(stderr, "mprotect failed");
36 
37  free(allocation);
38 
39 }
40 
41 

1 个解决方案

#1


15  

You need to use munmap for that. You don't need to do anything else (change protection bits etc). But you should check the return code of munmap.

你需要使用munmap。您不需要做任何其他事情(更改保护位等)。但你应该检查munmap的返回码。

munmap(allocation, 5000);

free(3) can only be used to free memory allocated via malloc(3).

free(3)只能用于释放通过malloc(3)分配的内存。

#1


15  

You need to use munmap for that. You don't need to do anything else (change protection bits etc). But you should check the return code of munmap.

你需要使用munmap。您不需要做任何其他事情(更改保护位等)。但你应该检查munmap的返回码。

munmap(allocation, 5000);

free(3) can only be used to free memory allocated via malloc(3).

free(3)只能用于释放通过malloc(3)分配的内存。