i686-elf-gcc -T linker.ld -o bin/kernel.bin -ffreestanding -O2 -nostdlib
src/boot.o src/gdt.o src/cgdt.o src/kernel.o -lgcc
src/cgdt.o: In function `gdt_set_gate':
cgdt.c:(.text+0x0): multiple definition of `gdt_set_gate'
src/gdt.o:gdt.c:(.text+0x0): first defined here
src/cgdt.o: In function `gdt_install':
cgdt.c:(.text+0x70): multiple definition of `gdt_install'
src/gdt.o:gdt.c:(.text+0x70): first defined here
src/gdt.o: In function `gdt_install':
gdt.c:(.text+0x17a): undefined reference to `gdt_flush'
src/cgdt.o: In function `gdt_install':
cgdt.c:(.text+0x17a): undefined reference to `gdt_flush'
collect2: error: ld returned 1 exit status
Makefile:17: recipe for target 'link' failed
make: *** [link] Error 1

CC=i686-elf-gcc
AS=i686-elf-as
LINKER=i686-elf-gcc

CFLAGS=-std=gnu99 -ffreestanding -O2 -Wall -Wextra -I./src/include
LDFLAGS=-T linker.ld

C_SOURCES = $(shell ls src/*.c)
ASM_SOURCES = $(shell ls src/*.s)
OBJECTS = $(ASM_SOURCES:.s=.o) $(C_SOURCES:.c=.o)

all: $(OBJECTS) link
clean:
    -rm ./src/*.o

link:
    $(LINKER) $(LDFLAGS) -o bin/kernel.bin -ffreestanding -O2 -nostdlib $(OBJECTS) -lgcc

.c.o:
    $(CC) $(CFLAGS) -c $< -o $@

.s.o:
    $(AS) $< -o $@