c中的 fopen():分段故障

Question

我正在尝试包装C库函数malloc免费和检测是否有内存泄漏在我的代码。我扩展了malloc/free函数，添加了一个fprintf函数，将malloc/free的地址和大小写入文件。

使用gcc或clang编译此代码会在fopen()行中出现分段错误。下面是命令:

gcc -o mainapp main.c -Wall -Wextra

我将fopen放在malloc和free函数内，但也得到同样的问题:分段错误(核心转储)

我找不到这个问题的解释。

下面是我的完整代码:

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#define __USE_GNU
#include <dlfcn.h>
#define TEST_MEM_LEAK 1 // a value of 1 means to join the memory leak detection, and a value of 0 means not to join
#if TEST_MEM_LEAK
typedef void *(*malloc_t)(size_t size);
malloc_t malloc_f = NULL;
typedef void (*free_t)(void *p);
free_t free_f = NULL;
int malloc_flag = 1;    // It is used to prevent repeated recursion and cannot exit because the printf function will call malloc for memory allocation
int free_flag = 1;
const char* logFileName = "/home/hammamiw/Documents/HeapMonitor/allocs.log";
FILE* fp = NULL;
void initCheck()
{
fp = fopen("/home/hammamiw/Documents/HeapMonitor/allocs.log", "w");
}
void *malloc(size_t size)
{
if(malloc_flag) { 
initCheck();  
malloc_flag = 0;  // Used to prevent printf from causing an error when calling malloc recursively
void *p = malloc_f(size);
fprintf(fp, "malloc, %lx, %lun", (uintptr_t)p, size);
//printf("mn");
malloc_flag = 1;  // It is used to ensure that the initial value of flag flag is consistent when malloc in this file is called again
return p;
} 
else {
return malloc_f(size);  // Here, the malloc function in the system library obtained by dlsym is called
}   
}
void free(void *p) 
{
initCheck();
if(free_flag) {
//initCheck();  
free_flag = 0;
fprintf(fp, "F, %lxn", (uintptr_t)p);
//printf("fn");
free_f(p);
free_flag = 1;
} else {
free_f(p);
}
}
#endif
int main()
{
#if TEST_MEM_LEAK // the part from if to endif can be divided into function calls
malloc_f = dlsym(RTLD_NEXT, "malloc");
if(!malloc_f) {
printf("load malloc failed: %sn", dlerror());
return 1;
}
free_f = dlsym(RTLD_NEXT, "free");
if(!free_f) {
printf("load free failed: %sn", dlerror());
return 1;
}
#endif
void *p1 = malloc(10);  //The malloc function in this article will be called first
void *p2 = malloc(20);

//Here, p2 is not released and there is a memory leak. Judge by checking whether the number of malloc and free times printed is the same
free(p2);
free(p1);
return 0;
}

注意:如果我使用printf而不是fprintf ->打印"f"one_answers";m">

环境:Ubuntu 22.04, C语言，GCC编译器版本11.3.0

Answer 1

需要先设置malloc_flag，再调用fopen()。然后，您不仅可以通过fprintf()，还可以通过fopen()来防止递归。