在C程序中找到崩溃的来源

Question

I have a code base where the process running on linux is crashing in free and sometimes in malloc:

#0  0xffffe430 in __kernel_vsyscall ()
#1  0xf7424e30 in raise () from /lib/libc.so.6
#2  0xf7426765 in abort () from /lib/libc.so.6
#3  0xf7469d33 in malloc_printerr () from /lib/libc.so.6
#4  0xf746e7bc in free () from /lib/libc.so.6
#5  0xf6047e25 in myFree (mem_ptr=0x82165d8) at ../my_code/mylib.c:78
#6  0xf6014a10 in FreeBuffer (buffer=0x82042f8)

In the code I am not seeing anything fishy at the place where memory freeing is happening. Function myFree() has nothing but a free() function call.

void FreeBuffer(struct MY_BUFFER *buffer)
{
    if (buffer)
    {
        myFree(buffer);
    }
}


void myFree(void *mem_ptr)
{

        free(mem_ptr);
}

I tried using MALLOC_CHECK_ but it was not of any help.

I suspect some where the heap is getting corrupted and want to find that. Any hint to proceed to debug the process in such cases?

Answer 1

There is hard to be 100% sure but most probably you are trying to free memory twice. It's great that you are checking if pointer is not NULL before trying to free it

if (buffer)
    {
        myFree(buffer);
    }

but you are probably NOT setting pointer NULL after doing exact free job - that's my guess.

Check if you have something like this

struct MY_BUFFER *buffer;
//do something with buffer
FreeBuffer(buffer)
buffer = NULL;

You can do this as well inside FreeBuffer() function but to do so you will have to pass address of pointer AKA pointer to pointer so the definition will be like this FreeBuffer(struct MY_BUFFER **buffer)