why does deleting printf function causes a SIGBUS error?-CodePudding

Im kinda new to C and I was trying to make a something like a malloc function just to practice pointers and all that stuff. everything worked fine but when I deleted printf functions in my main functions it returned SIGBUG error. from what I have read SIGBUS error is when processor tries to read from or write to memory that is not physically avaivable and I dont know what this have to do with deleting printf functions. I also tried the same code on other C and C compilers and it worked just fine without any errors.

here is the code:

#include <stdio.h>

#define heap_size 4096
#define m_availble 0x00
#define m_allocated 0x01
#define m_freed 0x02

typedef unsigned int uint;

char heap[heap_size]; //memory for Alloc function

void* Alloc(uint size);
void StoreInt(uint position, int value);
int GetInt(uint position);
void ShowHeap(uint position);

int main()
{
    int* MyPtr = (int*)Alloc(sizeof(int) * 4);
    MyPtr[0] = 69420;
    //printf("myptr adr1: %p\n", &MyPtr[1]);
    MyPtr[1] = 6;
    //printf("myptr adr2: %p\n", &MyPtr[2]);
    MyPtr[2] = 11;

    ShowHeap(0);
}

void* Alloc(uint size) //allocates memory inside heap
{
    uint position = 0;
    size  = sizeof(int)   sizeof(char);
    
    while(position   size   40 < heap_size )
    {
        if(heap[position] == m_availble)
        {
            /*m_availble means it can store memory at this position*/
            
            heap[position] = m_allocated;
            /*m_allocated means memory at this is position
            is allocated*/
            
            StoreInt(position   1, size);
            /*stores the size requied by user*/
            
            return &heap[(position   sizeof(int)  
                          sizeof(char))];
            /*returns pointer to adress that the user
            can write to or read from*/
        }
    }
    return NULL;
}

void StoreInt(uint position, int value)
{
    /*stores valeu in to the heap*/
    
    int* ptr = (int*)&heap[position];
    ptr[0] = value;
}

int GetInt(uint position)
{
    /*returns value from the heap*/
    
    int* ptr = (int*)&heap[position];
    return ptr[0];
}

void ShowHeap(uint position)
{
    /*display adresses with values stored at those
      adresses*/
    
    printf("HEAP:\n");
    for(int y = 0; y < 10; y  )
    {
        printf("adr: %p - ", &heap[position
                                   y * 4]);
            
        for(int x = 0; x < 4; x  )
        {
            printf("%i, ", heap[position   4 * y   x]);
        }
        printf("\n");
    }
}

CodePudding user response：

Alignment

If the alignment is not correct the below is undefined behavior and may cause a bus fault.

char heap[heap_size]; //memory for Alloc function

// StoreInt()
void StoreInt(uint position, int value) {
  int* ptr = (int*)&heap[position];
  ptr[0] = value;

// GetInt()
  int* ptr = (int*)&heap[position];
  return ptr[0];

Alternative, use memcpy():

// StoreInt()
void StoreInt(uint position, int value) {
  memcpy(&heap[position], &value, sizeof value);

// GetInt()
  int x;
  memcpy(&x, &heap[position], sizeof x);
  return x;

I also tried the same code on other C and C compilers and it worked just fine without any errors.

Other compilers may have different alignment requirements for types like int.

Casting

Casting is a whiff of code smell. Cast is only sporadically needed in C. In OP's code, all the casts smell.

char may be signed

Likely more informative output in ShowHeap() had heap[] been unsigned char than char.

Really want negative output -128 to 127 from printf("%i, ", heap[position 4 * y x]); or 0 to 255?