Well I've tried learning it by looking at the
sources from GazOS, but it makes no sense to me
...
Setting up a stack ...
-
K.J.
RE:Setting up a stack ...
>On 2002-03-21 15:11:19, The Legend wrote:
>Well I've tried learning it by looking at the
>sources from GazOS, but it makes no sense to me
>...
Here's what's in Chris Giese's kstart.asm
== start of snipt ==
; stop using bootloader GDT, and load new GDT
lgdt [gdt_ptr]
mov ax,LINEAR_DATA_SEL
mov ds,ax
mov es,ax
mov ss,ax
mov fs,ax
mov gs,ax
jmp LINEAR_CODE_SEL:sbat
sbat:
; zero the C language BSS
; 'bss' and 'end' are defined in the linker script file
EXTERN bss, end
mov edi,bss
mov ecx,end
sub ecx,edi
xor eax,eax
rep stosb
mov esp,stack ; set up stack
== bunch of code left out ==
SECTION .bss
resd 1024
stack:
== end of snippit ==
That's how his sets up a stack. However, I don't get how the code works exactly. He declares "stack" AFTER a bunch of space is made. It seems to me that it should be BEFORE the space but I'm not sure.
K.J.
>Well I've tried learning it by looking at the
>sources from GazOS, but it makes no sense to me
>...
Here's what's in Chris Giese's kstart.asm
== start of snipt ==
; stop using bootloader GDT, and load new GDT
lgdt [gdt_ptr]
mov ax,LINEAR_DATA_SEL
mov ds,ax
mov es,ax
mov ss,ax
mov fs,ax
mov gs,ax
jmp LINEAR_CODE_SEL:sbat
sbat:
; zero the C language BSS
; 'bss' and 'end' are defined in the linker script file
EXTERN bss, end
mov edi,bss
mov ecx,end
sub ecx,edi
xor eax,eax
rep stosb
mov esp,stack ; set up stack
== bunch of code left out ==
SECTION .bss
resd 1024
stack:
== end of snippit ==
That's how his sets up a stack. However, I don't get how the code works exactly. He declares "stack" AFTER a bunch of space is made. It seems to me that it should be BEFORE the space but I'm not sure.
K.J.
-
Marc Schütz
RE:Setting up a stack ...
>On 2002-03-22 23:36:23, K.J. wrote:
>SECTION .bss
>
> resd 1024
>stack:
>
>== end of snippit ==
>
>That's how his sets up a stack. However, I don't get how the code works exactly. He declares "stack" AFTER a bunch of space is made. It seems to me that it should be BEFORE the space but I'm not sure.
>
>K.J.
The way the stack is set up here is correct:
On the x86 the stack grows DOWN, not up
=> whenever you push something on the stack,
the stack pointer is DECREMENTED.
Therefore the stack pointer has to point to the
end of the stack.
>SECTION .bss
>
> resd 1024
>stack:
>
>== end of snippit ==
>
>That's how his sets up a stack. However, I don't get how the code works exactly. He declares "stack" AFTER a bunch of space is made. It seems to me that it should be BEFORE the space but I'm not sure.
>
>K.J.
The way the stack is set up here is correct:
On the x86 the stack grows DOWN, not up
=> whenever you push something on the stack,
the stack pointer is DECREMENTED.
Therefore the stack pointer has to point to the
end of the stack.
-
J. Weeks
RE:Setting up a stack ...
>
>The way the stack is set up here is correct:
>
>On the x86 the stack grows DOWN, not up
>=> whenever you push something on the stack,
>the stack pointer is DECREMENTED.
>
>Therefore the stack pointer has to point to the
>end of the stack.
Indeed.
But, just to play devil's advocate, and to make sure
some people new to this don't get the wrong idea; this
isn't necessarily true in pmode. You can, in fact,
have stacks that grow up, like a regular data
segment. It's defined the the segment descriptor.
Jeff
>The way the stack is set up here is correct:
>
>On the x86 the stack grows DOWN, not up
>=> whenever you push something on the stack,
>the stack pointer is DECREMENTED.
>
>Therefore the stack pointer has to point to the
>end of the stack.
Indeed.
But, just to play devil's advocate, and to make sure
some people new to this don't get the wrong idea; this
isn't necessarily true in pmode. You can, in fact,
have stacks that grow up, like a regular data
segment. It's defined the the segment descriptor.
Jeff