diff options
Diffstat (limited to 'asm')
| -rw-r--r-- | asm/GDT.asm | 3 | ||||
| -rw-r--r-- | asm/helpers.s | 43 | ||||
| -rw-r--r-- | asm/int_irq.asm | 1 | ||||
| -rw-r--r-- | asm/multiboot.s | 47 | ||||
| -rw-r--r-- | asm/usermode.s | 35 |
5 files changed, 85 insertions, 44 deletions
diff --git a/asm/GDT.asm b/asm/GDT.asm index f271377..444c313 100644 --- a/asm/GDT.asm +++ b/asm/GDT.asm @@ -15,6 +15,7 @@ ; global gdt_descriptor +global gdt_start gdt_start: @@ -76,3 +77,5 @@ CODE_SEG equ gdt_code - gdt_start DATA_SEG equ gdt_data - gdt_start CODE16_SEG equ gdt16_code - gdt_start DATA16_SEG equ gdt16_data - gdt_start + + diff --git a/asm/helpers.s b/asm/helpers.s new file mode 100644 index 0000000..6e89df6 --- /dev/null +++ b/asm/helpers.s @@ -0,0 +1,43 @@ +//http://wiki.osdev.org/GDT_Tutorial +.global setup_gdt + +// call as setup_gdt(GDT,sizeof(GDT)) +setup_gdt: + + // re-fill gdt_descriptor with new GDT location and size + movl 4(%esp),%eax + movl %eax, gdt_descriptor+2 + + movw 8(%esp),%ax + movw %ax, gdt_descriptor + // + + lgdt gdt_descriptor #load new descriptor table! + + // reload to take effect + reloadSegments: + + #Reload CS register containing code selector: + jmp $0x08,$reload_CS # 0x08 points at the new code selector + + reload_CS: + mov $0x10, %ax #0x10 points at the new data selector + mov %ax, %ds + mov %ax, %es + mov %ax, %fs + mov %ax, %gs + mov %ax, %ss + + tss_flush: + + movb $0x2B,%ax # Load the index of our TSS structure - The index is + # 0x28, as it is the 5th selector and each is 8 bytes + # long, but we set the bottom two bits (making 0x2B) + # so that it has an RPL of 3, not zero. + ltr %ax # Load 0x2B into the task state register. + + ret + + + +ret diff --git a/asm/int_irq.asm b/asm/int_irq.asm index e9864f0..ac8eef8 100644 --- a/asm/int_irq.asm +++ b/asm/int_irq.asm @@ -127,7 +127,6 @@ int_irq13: int_irq14: cli - pop eax call exception_handle_14 ;this will never return due to panic! jmp $ 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: diff --git a/asm/usermode.s b/asm/usermode.s new file mode 100644 index 0000000..acf4b04 --- /dev/null +++ b/asm/usermode.s @@ -0,0 +1,35 @@ +.global asm_usermode +.extern userfunc + +# pass address to func to exec (TODO) +asm_usermode: + + // 0x23 is user data segment (|2 low bits) + // 0x1b is user code segment (|2 low bits) + + // set segment registers + mov $0x23, %ax + mov %ax, %ds + mov %ax, %es + mov %ax, %fs + mov %ax, %gs + // ss is handled by iret + + mov %esp, %eax + + pushl $0x23 // user data segment + pushl %eax // current stack + pushf // + + // http://x86.renejeschke.de/html/file_module_x86_id_145.html + //mov $0x200, %eax + //push %eax // eflags image + pushl $0x1B // return code segment selector + push $userfunc // return instruction pointer + iret + + jmp . // will never be reached? + + + + |