macro expansion expected but failed by gcc

ITchimp · **Joined:** Sat Aug 18, 2018 8:44 pm **Posts:** 127

My header file (low_level.h)

Code:

#ifdef LOW_LEVEL_H
#define LOW_LEVEL
#define inb(p) port_byte_in(p)
#define outb(p, b) port_byte_out(p,b)

unsigned char port_byte_in(unsigned short port)
void port_byte_out(unsigned short port, unsigned char data)
#endif

my library implementation source file (low_level.c)

Code:

#include "low_level.h"
unsigned char port_byte_in(unsigned short port){
   unsigned char result;
   asm(" in %%dx, %%al":"=a"(result):"d" (port));
   return result;
}
void port_byte_out(unsigned short port, unsigned char data){
   asm("out %%al, (%%dx)"::"a"(data), "d"(port));
}

my main.c

Code:

#include "low_level.h"
#include <stdio.h>

void main(){
      port_byte_out(0x10, 14);
      outb(0x10,14);
}

compile with gcc gives me linking error indicating symbol outb not found.. but isn't it a macro
which gcc should expand?

iansjack · **Posted:** Wed Jun 03, 2020 4:29 am

Well....

You've wrapped your header file in

Code:

#ifdef LOW_LEVEL_H
...
#endif

LOW_LEVEL_H isn't defined, so the header never gets included. You'll also note the mistake in the second line of your header.

This explains your initial problem, but fixing it then throws up a further one. I think it's a useful exercise for you to try to solve that one yourself.

OSDev.org

macro expansion expected but failed by gcc

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