getting warning "assignment makes integer from pointer without a cast"


I get this warning on line 59:

assignment makes integer from pointer without a cast.

How can I fix it? Here is the whole file (copied from

/* bkerndev - Bran's Kernel Development Tutorial
*  By:   Brandon F. (
*  Desc: Global Descriptor Table management
*  Notes: No warranty expressed or implied. Use at own risk. */

/* Defines a GDT entry */
struct gdt_entry
    unsigned short limit_low;
    unsigned short base_low;
    unsigned char base_middle;
    unsigned char access;
    unsigned char granularity;
    unsigned char base_high;
} __attribute__((packed));

struct gdt_ptr
    unsigned short limit;
    unsigned int base;
} __attribute__((packed));

/* Our GDT, with 3 entries, and finally our special GDT pointer */
struct gdt_entry gdt[3];
struct gdt_ptr gp;

/* This is in start.asm. We use this to properly reload
*  the new segment registers */
extern void _gdt_flush();

/* Setup a descriptor in the Global Descriptor Table */
void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran)
    /* Setup the descriptor base address */
    gdt[num].base_low = (base & 0xFFFF);
    gdt[num].base_middle = (base >> 16) & 0xFF;
    gdt[num].base_high = (base >> 24) & 0xFF;

    /* Setup the descriptor limits */
    gdt[num].limit_low = (limit & 0xFFFF);
    gdt[num].granularity = ((limit >> 16) & 0x0F);

    /* Finally, set up the granularity and access flags */
    gdt[num].granularity |= (gran & 0xF0);
    gdt[num].access = access;

/* Should be called by main. This will setup the special GDT
*  pointer, set up the first 3 entries in our GDT, and then
*  finally call gdt_flush() in our assembler file in order
*  to tell the processor where the new GDT is and update the
*  new segment registers */
void gdt_install()
    /* Setup the GDT pointer and limit */
    gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
    gp.base = &gdt;

    /* Our NULL descriptor */
    gdt_set_gate(0, 0, 0, 0, 0);

    /* The second entry is our Code Segment. The base address
    *  is 0, the limit is 4GBytes, it uses 4KByte granularity,
    *  uses 32-bit opcodes, and is a Code Segment descriptor.
    *  Please check the table above in the tutorial in order
    *  to see exactly what each value means */
    gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);

    /* The third entry is our Data Segment. It's EXACTLY the
    *  same as our code segment, but the descriptor type in
    *  this entry's access byte says it's a Data Segment */
    gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);

    /* Flush out the old GDT and install the new changes! */
asked on Stack Overflow Nov 3, 2012 by Gintas_ • edited Nov 4, 2012 by Lekensteyn

3 Answers


OK, let me put this in context...

struct gdt_ptr
    unsigned short limit;
    unsigned int base;
} __attribute__((packed));

struct gdt_entry gdt[3];
struct gdt_ptr gp;

gp.base = &gdt;

You are assigning a pointer (&gdt) to an integer (gp.base) - hence the error :-)

I suspect that you actually want (or something similar to):

struct gdt_ptr
    unsigned short limit;
    struct gdt_entry *base;
} __attribute__((packed));

Alternatively, since you are later evaluating the address as its component fields, leave the definition as is, and cast the assignment

answered on Stack Overflow Nov 3, 2012 by Andrew

I heard addresses should be keeps in size_t, but i you really want keep address in int maybe just cast it? gp.base = (int) &gdt;

answered on Stack Overflow Nov 4, 2012 by Mateusz

I had met this problem before, Type casting works:

gp.base = (unsigned int)&gdt
answered on Stack Overflow Nov 4, 2019 by S.K.

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