c - 为什么在 GCC 编译运行正常时 GDB 显示段错误

Question

我正在写一个小代码来分配空间并在其中读写以测试缓存监控工具。代码如下:

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

#define times 2

void write_in_space(int* x, int size){
  printf("\n Entering write in space \n");
  int i;
  for(i = 0; i< size; i++){
    *(x + i) = i;
    i++;
  }
  printf("\n Exiting write_in_space \n");
}

void read_in_space(int* x, int size){

  printf("\n Entering read_in_space \n");
  int i = 0;
  while(i < size){
    *(x + i);
    i++;
  }
  printf("\n Exiting read_in_space \n");
}

void assign_and_work(int k, int l, int m, int mm){

  printf("\n Entering assign_and_work \n");
  int* space;
  space = (int*)malloc(k * sizeof(int));

  if(mm == 3){
  write_in_space(space , k);
  sleep(m);
  read_in_space(space, l);
}

  else if(mm == 1)
    read_in_space(space, l);

  else if(mm == 2)
    write_in_space(space,k);


  printf("\n Exiting assign_and_work \n");
  free(space);

}

//Driver Code

int main(int argc, char **argv){
  int read_space = 0;
  int write_space = 0;
  int sleep_time = 0;
  int i = 1;
  int mode = -1;
  int time = times;
  do{
    if(strcmp(argv[i],"-w") == 0)
      write_space = atoi(argv[i + 1]);
    if(strcmp(argv[i],"-r") == 0)
      read_space = atoi(argv[i + 1]);
    if(strcmp(argv[i],"-s") == 0)
      sleep_time = atoi(argv[i + 1]);
    //if(strcmp(argv[i],"-time") == 0)
      //times = atoi(argv[i + 1]);
    i = i + 1;
  }while( i < argc);

  if(write_space == 0 && read_space > 0)
    mode = 1;
  else if(read_space == 0 && write_space > 0)
    mode = 2;
  else
    mode = 3;

  if((read_space > write_space) && (mode == 3) ){
    write_space = read_space;
  }
    while(time > 0){
    assign_and_work(write_space, read_space, sleep_time, mode);
    time--;
  }


return 0;

}

问题是当我使用命令编译时

gcc -o rw readwrite.c

并运行 ./rw -r 500000 -w 800000 -s 20 它工作正常。但是当我尝试使用 gdb 时，它显示以下消息

Program received signal SIGSEGV, Segmentation fault.

__strcmp_sse2_unaligned () at ../sysdeps/x86_64/multiarch/strcmp-sse2-unaligned.S:31
31  ../sysdeps/x86_64/multiarch/strcmp-sse2-unaligned.S: No such file or directory.
(gdb) 

我无法理解错误。我尝试使用 gdb，因为当我通过 argv 将时间作为用户输入时，它显示核心已转储。

 if(strcmp(argv[i],"-time") == 0)
      times = atoi(argv[i + 1]);

请帮助我了解错误。我搜索了很多但无法弄清楚。先谢谢你。

Answer 1

我猜你没有将参数传递给 GDB，它在第 63 行尝试将不存在的参数与选项进行比较时失败了。这是失败的根源。

尝试在没有 args 的情况下使用你的程序，看看它是否也失败了。

如果所有参数都是强制性的，您应该在第 62 行之前放置一个 if 来检查提供的参数数量是否正确。