在MacOSX 10.8.2下使用XCode 4.6进行写入的mmap会使程序崩溃 [英] mmap for write under MacOSX 10.8.2 with XCode 4.6 will make program crash

问题描述

我尝试使用XCode 4.6在MacOSX 10.8.2下运行mmap的简单测试.该程序如下所示，映射为读取的文件是可以的，而对写指针"target"的访问将使程序崩溃. 错误消息是"EXC_BAD_ACCESS".

I try to run a simple test of mmap under MacOSX 10.8.2, with XCode 4.6. This program is as follows, the file mapped for read is OK while the access to the write pointer "target" will make the program crash. Error message is "EXC_BAD_ACCESS".

有人和我有同样的案子吗? 非常感谢.

Does anyone have the same case with me ? Thanks a lot.

#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, const char * argv[]) {
int input, output;
size_t size;

char *source, *target;

input = open("SEK2.txt", O_RDONLY);
if (input == -1) {
    printf("Open source file failed");
    return -1;
}
output = open("test.txt", O_RDWR|O_CREAT|O_TRUNC);
if (output == -1) {
    printf("Open Output file failed");
    return -1;
}

size = lseek(input, 0, SEEK_END);
printf("File size = %d\n", size);

source = (char*)mmap(0, size, PROT_READ, MAP_PRIVATE, input, 0);
if ( source == (void*)-1) {
    printf("Source MMap Error\n");
    return -1;
}

target = (char*)mmap(0, size, PROT_EXEC, MAP_PRIVATE, output, 0);
if ( target == (void*)-1 ) {
    printf( "Target MMap Error\n");
    return -1;
}

memcpy(target, source, size); // EXC_BAD_ACCESS to "target"
munmap(source, size);
munmap(target, size);

close(input);
close(output);

printf("Successed");
return 0;

}

推荐答案

我认为您需要ftruncate(output, size);来使输出文件足够大.我不相信内核会自动增长文件来容纳写入映射地址的数据.

I think you need to ftruncate(output, size); to make the output file large enough. I don't believe the kernel with automatically grow a file to accommodate data written to the mapped addresses.

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