c - 奇怪的 mmap 行为

Question

在我的机器上，test_anon_shared 似乎可以工作，而 test_anon 因“无效参数”错误而失败。知道我哪里出错了吗？

#include <unistd.h>
#include <sys/mman.h>

#include <stdio.h>
#include <stdlib.h>

void *test_anon(void) {
  printf("testing MAP_ANONYMOUS only!\n");
  void *mem = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
                   MAP_ANONYMOUS, -1, 0);
  if (mem == MAP_FAILED) {
    perror("test_anon");
    abort();
  }
}

void *test_anon_shared(void) {
  printf("testing MAP_ANONYMOUS | MAP_SHARED!\n");
  void *mem = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
                   MAP_ANONYMOUS | MAP_SHARED, -1, 0);
  if (mem == MAP_FAILED) {
    perror("test_anon_shared");
    abort();
  }
}

int main(void) {
  printf("test_anon_shared = %p\n", test_anon_shared());
  printf("test_anon = %p\n", test_anon());
}

Answer 1

您的标志中必须包含 MAP_SHARED 或 MAP_PRIVATE 之一。 mmap(2)手册页:

[...] This behavior is determined by including exactly one of the following values in flags:

   MAP_SHARED [...]
   MAP_PRIVATE [...]