Question

我在vmware 11.0和linux-2.6.34上遇到了这个问题，gcc 4.9.2，没有在真实硬件上测试过。代码运行成功后，打印的消息没有SIGSEGV。但如果我在munmap之前取消注释printf，就会发现一个SIGSEGV。

在munmap（）之前和之后的地图打印在以下消息中。

static void check_mmap(void){
    int fd, i;
    char *p = NULL;

    if ((fd = shm_open("xxxxxxxxxxxx", O_RDWR|O_CREAT|O_TRUNC, 0666)) == -1) {
        printf("open shm file failed.\n");
        return;
    }

    if (ftruncate(fd, 4096) == -1)
        goto out;

    p = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
    if (MAP_FAILED == p)
    goto out;

    //printf("Mapped at %p\n", p);
    getchar(); // <----- chance to print maps befor munmap

    if (munmap(p, 4096) != 0)
        printf("munmap error: %s\n", strerror(errno));

    printf("Corrupting mmap memory.\n");
    for(i = 0; i < 4095; i ++)
        p[i] = 0;
    printf("Done\n");

    getchar(); // <----- chance to print maps after munmap

out:
    close(fd);
    if (p)
        munmap(p, 4096);
}

在munmap之前映射，shm xxxxxxxxxxxx在7f3f2683a000-7f3f2683b000进行映射

00400000-00401000 r-xp 00000000 00:14 121 / mnt / hgfs / vm_shared / asan / asan1

00600000-00601000 rw-p 00000000 00:14 121 / mnt / hgfs / vm_shared / asan / asan1

7f3f25ea6000-7f3f25ebd000 r-xp 00000000 08:02 347266 /lib64/libpthread-2.11.3.so

7f3f25ebd000-7f3f260bc000 --- p 00017000 08:02 347266 /lib64/libpthread-2.11.3.so

7f3f260bc000-7f3f260bd000 r - p 00016000 08:02 347266 /lib64/libpthread-2.11.3.so

7f3f260bd000-7f3f260be000 rw-p 00017000 08:02 347266 /lib64/libpthread-2.11.3.so

7f3f260be000-7f3f260c2000 rw-p 00000000 00:00 0

7f3f260c2000-7f3f2620e000 r-xp 00000000 08:02 298091 /lib64/libc-2.11.1.so

7f3f2620e000-7f3f2640d000 --- p 0014c000 08:02 298091 /lib64/libc-2.11.1.so

7f3f2640d000-7f3f26411000 r - p 0014b000 08:02 298091 /lib64/libc-2.11.1.so

7f3f26411000-7f3f26412000 rw-p 0014f000 08:02 298091 /lib64/libc-2.11.1.so

7f3f26412000-7f3f26417000 rw-p 00000000 00:00 0

7f3f26417000-7f3f2641e000 r-xp 00000000 08:02 335978 /lib64/librt-2.11.1.so

7f3f2641e000-7f3f2661d000 --- p 00007000 08:02 335978 /lib64/librt-2.11.1.so

7f3f2661d000-7f3f2661e000 r - p 00006000 08:02 335978 /lib64/librt-2.11.1.so

7f3f2661e000-7f3f2661f000 rw-p 00007000 08:02 335978 /lib64/librt-2.11.1.so

7f3f2661f000-7f3f2663d000 r-xp 00000000 08:02 260202 /lib64/ld-2.11.1.so

7f3f2682b000-7f3f2682e000 rw-p 00000000 00:00 0

7f3f26839000-7f3f2683a000 rw-p 00000000 00:00 0

7f3f2683a000-7f3f2683b000 rw-p 00000000 00:11 16078 / dev / shm / xxxxxxxxxxxx

7f3f2683b000-7f3f2683c000 rw-p 00000000 00:00 0

7f3f2683c000-7f3f2683d000 r - p 0001d000 08:02 260202 /lib64/ld-2.11.1.so

7f3f2683d000-7f3f2683e000 rw-p 0001e000 08:02 260202 /lib64/ld-2.11.1.so

7f3f2683e000-7f3f2683f000 rw-p 00000000 00:00 0

7fffd9ce3000-7fffd9d04000 rw-p 00000000 00:00 0 [stack]

7fffd9dff000-7fffd9e00000 r-xp 00000000 00:00 0 [vdso]

ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]

在munmap之后映射，shm已成功取消映射。