Conflicting types and previous declaration of function?

Question

While using make to compile an OS I've got a weird error from make that I don't understand.

from make:

source/paging.c:179:6: error: conflicting types for ‘page_fault’
headers/paging.h:68:6: note: previous declaration of ‘page_fault’ was here
make: *** [obj/paging.o] Error 1

The function(s) in question are the ones that follow. I haven't included the whole file of paging.c as it is very big, same goes for paging.h tbh, but if you want to see the header file I will post the rest.

paging.c:

....
....
void page_fault(registers_t regs)
{
// A page fault has occurred.
// The faulting address is stored in the CR2 register.
u32int faulting_address;
asm volatile("mov %%cr2, %0" : "=r" (faulting_address));

// The error code gives us details of what happened.
int present   = !(regs.err_code & 0x1); // Page not present
int rw = regs.err_code & 0x2;           // Write operation?
int us = regs.err_code & 0x4;           // Processor was in user-mode?
int reserved = regs.err_code & 0x8;     // Overwritten CPU-reserved bits of page entry?
int id = regs.err_code & 0x10;          // Caused by an instruction fetch?

// Output an error message.
monitor_write("Page fault! ( ");
if (present) {monitor_write("present ");}
if (rw) {monitor_write("read-only ");}
if (us) {monitor_write("user-mode ");}
if (reserved) {monitor_write("reserved ");}
monitor_write(") at 0x");
monitor_write_hex(faulting_address);
monitor_write("\n");
PANIC("Page fault");
}

paging.h:

....
....
void page_fault(registers_t *regs);
....
....

NOTE: This is from a tutorial ( so it should be working, but I have come into a problem with the provided source code before where one function wasn't spelt properly ).

Any idea's why make is complaining?

Thanks.

make errors without *:

obj/interrupt.o: In function `isr_common_stub':
asem/interrupt.s:(.text+0x1c9): undefined reference to `isr_handler'
obj/interrupt.o: In function `irq_common_stub':
asem/interrupt.s:(.text+0x1ee): undefined reference to `irq_handler'
obj/main.o: In function `main':
main.c:(.text+0x6e): undefined reference to `placement_address'
obj/descriptor_tables.o: In function `init_descriptor_tables':
descriptor_tables.c:(.text+0x23): undefined reference to `interrupt_handlers'
obj/timer.o: In function `init_timer':
timer.c:(.text+0x30): undefined reference to `register_interrupt_handler'
obj/paging.o: In function `initialise_paging':
paging.c:(.text+0x298): undefined reference to `kmalloc'
paging.c:(.text+0x2cc): undefined reference to `kmalloc_a'
paging.c:(.text+0x328): undefined reference to `placement_address'
paging.c:(.text+0x341): undefined reference to `register_interrupt_handler'
obj/paging.o: In function `get_page':
paging.c:(.text+0x3da): undefined reference to `kmalloc_ap'
obj/initrd.o: In function `initialise_initrd':
initrd.c:(.text+0x1f1): undefined reference to `kmalloc'
initrd.c:(.text+0x2f5): undefined reference to `kmalloc'
initrd.c:(.text+0x402): undefined reference to `kmalloc'
obj/task.o: In function `initialise_tasking':
task.c:(.text+0x24): undefined reference to `kmalloc'
task.c:(.text+0x9a): undefined reference to `kmalloc_a'
obj/task.o: In function `fork':
task.c:(.text+0x2b3): undefined reference to `clone_directory'
task.c:(.text+0x2c2): undefined reference to `kmalloc'
task.c:(.text+0x314): undefined reference to `kmalloc_a'
obj/syscall.o: In function `initialise_syscalls':
syscall.c:(.text+0x8b): undefined reference to `register_interrupt_handler'
make: *** [kern/kernel] Error 1

interrupt.s:

....
; In isr.c
extern irq_handler
....
....
; In isr.c
extern isr_handler

main.c: .... extern u32int placement_address; ....

descriptor_tables.c:

void init_descriptor_tables()
{

// Initialise the global descriptor table.
init_gdt();
// Initialise the interrupt descriptor table.
init_idt();
// Nullify all the interrupt handlers.
memset(&interrupt_handlers, 0, sizeof(isr_t)*256);
}

timer.c:

void init_timer(u32int frequency)
{
// Firstly, register our timer callback.
register_interrupt_handler(IRQ0, &timer_callback);

// The value we send to the PIT is the value to divide it's input clock
// (1193180 Hz) by, to get our required frequency. Important to note is
// that the divisor must be small enough to fit into 16-bits.
u32int divisor = 1193180 / frequency;

// Send the command byte.
outb(0x43, 0x36);

// Divisor has to be sent byte-wise, so split here into upper/lower bytes.
u8int l = (u8int)(divisor & 0xFF);
u8int h = (u8int)( (divisor>>8) & 0xFF );

// Send the frequency divisor.
outb(0x40, l);
outb(0x40, h);
}

paging.c:

....
void initialise_paging()
{
// The size of physical memory. For the moment we 
// assume it is 16MB big.
u32int mem_end_page = 0x1000000;

nframes = mem_end_page / 0x1000;
frames = (u32int*)kmalloc(INDEX_FROM_BIT(nframes));
memset(frames, 0, INDEX_FROM_BIT(nframes));

// Let's make a page directory.
kernel_directory = (page_directory_t*)kmalloc_a(sizeof(page_directory_t));
current_directory = kernel_directory;

// We need to identity map (phys addr = virt addr) from
// 0x0 to the end of used memory, so we can access this
// transparently, as if paging wasn't enabled.
// NOTE that we use a while loop here deliberately.
// inside the loop body we actually change placement_address
// by calling kmalloc(). A while loop causes this to be
// computed on-the-fly rather than once at the start.
int i = 0;
while (i < placement_address)
{
    // Kernel code is readable but not writeable from userspace.
    alloc_frame( get_page(i, 1, kernel_directory), 0, 0);
    i += 0x1000;
}
// Before we enable paging, we must register our page fault handler.
register_interrupt_handler(14, page_fault);

// Now, enable paging!
switch_page_directory(kernel_directory);
}

Answer 1

You have two differing signatures for a function with the same name. Note that the first declaration takes a registers_t , but the second takes a registers_t* .

/* paging.h */
void page_fault(registers_t *regs);

/* paging.c */
void page_fault(registers_t regs)

The function signature in paging.c is correct per the usage of the variable regs , so change the declaration in the .h file to match.

It really stinks, but I have run into problems like this in distributed source code before (especially in school...). Not sure how code that won't even compile can make it out into the wild like this, but it happens.

Answer 2

The function signatures don't match:

Declaration in .h file:

void page_fault(registers_t *regs)

Definition in .c file:

void page_fault(registers_t regs)

Correct the signature in header file to match the one in the .c file (ie remove the * from paging.h ).