Segmentation fault for a weird unknown reason - c

Question

I get a segmentation fault (core dumped) in the following peace of code (I'm implementing malloc(), free() and realloc()):
void free(void* ptr)
{
void* curr = head;
void* before = NULL;
int isLegal = 0;
/*Line X*/printf("curr is %p and ptr is %p\n", curr, ptr);
if(curr == ptr)
{
printf("aaa");
}
else
{
printf("bbb");
}
/*Some more code that actually frees the pointer and not relevant here*/
}
Now, you'd assume that it'd print aaa or bbb, it just announces a segmentation fault right after performing the printf() in line X. If I type "printf("a")" instead of the current printf() it won't print 'a' at all. That is really weird.
It prints:
curr is 0x86be000 and ptr is 0x86be000
and yet it would just exit and throw a segmentation fault right after.
The variable head is a static variable in that file. I really want to know where the problem is, it's really weird. Here's the statement from the header file:
void free(void* ptr);
As simple as that, do you see any problem in here?
The full code is available here but I doubt it's related, the program should, at least, print either 'aaa' or 'bbb', and it doesn't do that.
Any idea? I'm really desperate.

Answer 1

Following code complied with warnings but did execute perfectly
#include <unistd.h>
typedef struct metadata_block* p_block;
typedef struct metadata_block
{
size_t size;
p_block next;
int free;
}metadata_block;
void* malloc(size_t size);
void free(void* ptr);
void* realloc(void* ptr, size_t size);
//THE MAIN CODE IS AT THE BOTTOM//
#include <stdio.h>
static p_block head = NULL;
void* malloc(size_t size)
{
void* ptr;
int isOk = 1;
int temp = 0;
p_block curr = head;
if(size <= 0)
{
return NULL;
}
if(curr)
{
while(curr->next && isOk)
{
if(curr->free && size <= curr->size)
{
isOk = 0;
}
if(isOk)
{
curr = curr->next;
}
}
if(isOk) //what will happen if there isn't one free and big enough
{
ptr = sbrk(size + sizeof(metadata_block));
if((int)ptr <= 0)
return NULL;
((p_block)(ptr))->size = size;
((p_block)(ptr))->next = NULL; //next run it's the real next.
((p_block)(ptr))->free = 0;
return (ptr + sizeof(metadata_block));
}
else
{
if(curr->next)
{
ptr = curr;
if(curr->size == size || size > (curr->size - sizeof(metadata_block) - 1)) //not enough room for another block of memory
{
((p_block)(ptr))->free = 0;
return (ptr + sizeof(metadata_block));
}
temp = curr->size;
((p_block)(ptr))->size = size;
((p_block)(ptr))->free = 0;
((p_block)(ptr + sizeof(metadata_block) + size))->next = curr->next;
((p_block)(ptr))->next = ptr + sizeof(metadata_block) + size;
((p_block)(ptr + sizeof(metadata_block) + size))->size = temp - size;
((p_block)(ptr + sizeof(metadata_block) + size))->free = 1;
return (ptr + sizeof(metadata_block));
}
else
{
ptr = curr;
if((int)sbrk(size - curr->size) > 0)
{
((p_block)(ptr))->size = size;
((p_block)(ptr))->next = NULL; //next run it's the real next.
((p_block)(ptr))->free = 0;
return (ptr + sizeof(metadata_block));
}
return NULL;
}
}
}
else
{
ptr = sbrk(size + sizeof(metadata_block));
if((int)ptr <= 0)
return NULL;
head = ptr;
((p_block)(ptr))->size = size;
((p_block)(ptr))->next = NULL;
((p_block)(ptr))->free = 0;
}
return ptr;
}
void free(void* ptr)
{
void* curr = head;
void* before = NULL;
int isLegal = 0;
printf("curr is %p and ptr is %p\n", curr, ptr);
if(curr == ptr)
{
printf("aaa\n");
}
else
{
printf("bbb\n");
}
if(curr && ptr)
{
while(curr && !isLegal)
{
if(((p_block)(ptr)) == ((p_block)(curr))->next)
{
before = curr;
isLegal = 1;
curr = ((p_block)(curr))->next;
}
else
{
curr = ((p_block)(curr))->next;
}
}
if(isLegal)
{
curr = curr - sizeof(metadata_block);
if(((p_block)(curr))->next)
{
((p_block)(curr))->free = 1;
}
else
{
sbrk(0-(((p_block)(curr))->size + sizeof(metadata_block)));
((p_block)(before))->next = NULL;
}
}
}
}
void* realloc(void* ptr, size_t size)
{
void* ptr2 = malloc(size);
int i;
for(i = 0 ; i < size ; i++)
{
*((char*)(ptr2 + i)) = *((char*)(ptr + i));
}
free(ptr);
return ptr2;
}
int main()
{
printf("I'm in.\n");
char * str = malloc(10);
printf("After Malloc()\n");
void * ptr = (void *) str;
void * ptr2;
if(!str)
{
printf("Fail.\n");
}
strcpy(str,"TEST!\0");
printf("About to free\n");
free(str);
printf("free: OK!\n");
}
Output :
I'm in.
After Malloc()
About to free
curr is 0x1049000 and ptr is 0x1049000
aaafree: OK!
note - Instaed of your mm.h include I included codes in same file