diff options
Diffstat (limited to 'asm/multiboot.s')
| -rw-r--r-- | asm/multiboot.s | 47 |
1 files changed, 4 insertions, 43 deletions
diff --git a/asm/multiboot.s b/asm/multiboot.s index 1927c9b..22be3d1 100644 --- a/asm/multiboot.s +++ b/asm/multiboot.s @@ -14,6 +14,7 @@ # You don't need to understand all these details as it is just magic values that # is documented in the multiboot standard. The bootloader will search for this # magic sequence and recognize us as a multiboot kernel. + .section .multiboot .align 4 .long MAGIC @@ -49,60 +50,20 @@ stack_top: .global stack_bottom .type _start, @function _start: - # Welcome to kernel mode! We now have sufficient code for the bootloader to - # load and run our operating system. It doesn't do anything interesting yet. - # Perhaps we would like to call printf("Hello, World\n"). You should now - # realize one of the profound truths about kernel mode: There is nothing - # there unless you provide it yourself. There is no printf function. There - # is no <stdio.h> header. If you want a function, you will have to code it - # yourself. And that is one of the best things about kernel development: - # you get to make the entire system yourself. You have absolute and complete - # power over the machine, there are no security restrictions, no safe - # guards, no debugging mechanisms, there is nothing but what you build. - - # By now, you are perhaps tired of assembly language. You realize some - # things simply cannot be done in C, such as making the multiboot header in - # the right section and setting up the stack. However, you would like to - # write the operating system in a higher level language, such as C or C++. - # To that end, the next task is preparing the processor for execution of - # such code. C doesn't expect much at this point and we only need to set up - # a stack. Note that the processor is not fully initialized yet and stuff - # such as floating point instructions are not available yet. - lgdt gdt_descriptor #load descriptor table! # To set up a stack, we simply set the esp register to point to the top of # our stack (as it grows downwards). movl $stack_top, %esp - # We are now ready to actually execute C code. We cannot embed that in an - # assembly file, so we'll create a kernel.c file in a moment. In that file, - # we'll create a C entry point called kernel_main and call it here. - push %ebx #pass address of the multiboot information data structure push %eax #pass eax, so kernel can check for magic number - - - reloadSegments: - #Reload CS register containing code selector: - jmp $0x08,$reload_CS # 0x08 points at the new code selector - - reload_CS: - mov $0x10, %ax - mov %ax, %ds - mov %ax, %es - mov %ax, %fs - mov %ax, %gs - mov %ax, %ss + call kernel_main - # In case the function returns, we'll want to put the computer into an - # infinite loop. To do that, we use the clear interrupt ('cli') instruction - # to disable interrupts, the halt instruction ('hlt') to stop the CPU until - # the next interrupt arrives, and jumping to the halt instruction if it ever - # continues execution, just to be safe. We will create a local label rather - # than real symbol and jump to there endlessly. + # should never be reached + cli hlt .Lhang: |