Specifying Linker Script
On your website the archive contains a typo in the
build.sh shell scripts where it forgets to give the command line option
-Tlinker.ld to the linker.
This causes the linker to leave the default virtual addresses for the sections, which of course in almost any case will not exist in memory during booting and did not in mine (since they are so high - around 128MB). The correct option is (below):
ld linker.ld loader.o kernel.o isr.o -o kernel.bin -Map kernel.map -Tlinker.ld
Stack Frame For C Calling Convention
Other than that it loads and raises a exception, I changed the
loader.s to setup a stack frame for when calling a C function.
Code: Select all
_loader:
mov $(stack + STACKSIZE), %esp # set up the stack
push %esp
mov %esp, %ebp
push %eax # Multiboot magic number
push %ebx # Multiboot data structure
call _main # call kernel proper
nop
hlt
I fiddled with the
main function, and added my own print message function which appeared to get rid of the exception.
Code: Select all
#define VGA_WIDTH 80
#define VGA_HEIGHT 25
void puts(char *message, unsigned int x, unsigned int y, unsigned char color)
{
unsigned int i;
unsigned short *vmem = (unsigned short*)0xB8000;
for(i = 0; message[i] != 0; ++i)
{
vmem[x + (y * VGA_WIDTH) + i] = (color << 8) | message[i];
}
return;
}
void _main(void* mbd,unsigned int magic)
{
unsigned short *vmem = (unsigned short*)0xB8000;
vmem[0] = (1 << 8) | 'a';
gdt_install();
idt_install();
//text_color(WHITE,BLACK);
clrscr();
puts("Hello World", 0, 0, 0x12);
}
Apparently, the problem is somewhere in your video routines.
Separating Function Implementations From Header Files
You should also definitely place all that code into a source file like frank suggestion earlier for example:
gdt.h : Example
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#ifndef _PYROS_GDT
#define _PYROS_GDT
void gdt_flush();
void gdt_set_gate(int num,unsigned long base, unsigned long limit, unsigned char access, unsigned char gran);
void gdt_install();
#endif
Code: Select all
/// Global Descriptor Table Utility Functions
/// gdt.c
///
struct gdt_entry gdt[3];
struct gdt_ptr gp;
void gdt_flush()
{
asm("lgdt %0":"=g"(gp));
}
void gdt_set_gate(int num,unsigned long base,unsigned long limit,unsigned char access,unsigned char gran)
{
gdt[num].base_low=(base&0xFFFF);
gdt[num].base_middle=(base>>16)&0xFF;
gdt[num].base_high=(base>>24)&0xFF;
gdt[num].limit_low=(limit&0xFFFF);
gdt[num].granularity=((limit>>16)&0x0F);
gdt[num].granularity|=(gran&0xF0);
gdt[num].access=access;
}
void gdt_install()
{
gp.limit=(sizeof(struct gdt_entry)*3)-1;
gp.base=(unsigned int)&gdt;
gdt_set_gate(0,0,0,0,0);
gdt_set_gate(1,0,0xFFFFFFFF,0x9A,0xCF);
gdt_set_gate(2,0,0xFFFFFFFF,0x92,0xCF);
gdt_flush();
}
If you try doing
#include gdt.h in two different source files the linker (LD) will complain that there are multiple symbol definitions.
Right now you do not have to worry about it since you are only compiling one source file implicitly.
gcc -o kernel.o -c main.c -nostdlib -nostartfiles -nodefaultlibs -fno-stack-protector
ld linker.ld loader.o test.o kernel.o isr.o -o kernel.bin -Map kernel.map -Tlinker.ld
However, if you do this:
gcc -o kernel.o -c main.c -nostdlib -nostartfiles -nodefaultlibs -fno-stack-protector
gcc -o test.o -c test.c -nostdlib -nostartfiles -nodefaultlibs -fno-stack-protector
ld linker.ld loader.o test.o kernel.o isr.o -o kernel.bin -Map kernel.map -Tlinker.ld
And the
test.c source file also does
#include "gdt.h", the linker will complain and abort linking.
Miscellaneous
I am so appreciative that your kernel would actually compile, although this might be attributed to it being extremely simple. I have tried compiling so many other's kernel and could never get it to work just simply because it was so darn complicated. Thanks for including a build script (build system) or some type and placing the kernel image where it could be easily noticed for loading.
