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Switch to PMode not working
Posted: Sat Sep 18, 2004 9:15 am
by chris
When I try this on my test computer it just hangs. I'm in the process of getting Bochs running so I can get some debug info.
Code: Select all
ORG 00000h
BITS 16
main:
mov ax, 07C00h
mov ds, ax
mov ax, 08000h
mov ss, ax
mov ax, 09000h
mov sp, ax
; Enable the A20 line.
call .enable_a20
; Reprogram the PIC.
; call .reprogPIC
; Re-enable the keyboard (if it's off)
mov al, 0AEh
mov dx, 064h
out dx, al
cli
lgdt [gdt_main]
lidt [idt_main]
mov eax, 000000011h
mov cr0, eax
jmp dword 008h:main32
; Candy's A20 Code:
.a20_tries db 00FFh
.empty_8042:
push cx
mov cx, 65535
.empty_8042_loop:
dec cx
jz .empty_8042_end_loop
mov dx, 064h
in al, dx
test al, 01h
jz .no_output
mov dx, 064h
in al, dx
jmp .empty_8042_loop
.no_output:
test al, 02h
jnz .empty_8042_loop
.empty_8042_end_loop:
pop cx
ret
.enable_a20:
.a20_none:
call .a20_test
jnz .a20_done
.a20_bios:
mov ax, 02401h
pushf
int 015h
popf
call .a20_test
jnz .a20_done
.a20_kbc:
call .empty_8042
call .a20_test
jnz .a20_done
mov al, 0D1h
mov dx, 064h
out dx, al
call .empty_8042
mov al, 0DFh
mov dx, 060h
out dx, al
call .empty_8042
mov dx, 092h
in al, dx
or al, 02h
and al, 0FEh
out dx, al
.a20_wait:
xor cx, cx
.a20_wait_loop:
call .a20_test
jnz .a20_done
loop .a20_wait_loop
mov bx, .a20_tries
dec byte [bx]
jnz .enable_a20
mov si, .a20_not_working
; call print_message_16
.crash:
hlt
jmp .crash
.crash:
hlt
jmp .crash
.a20_done:
ret
.a20_not_working db "Unable to enable A20 gate, booting failed."
.a20_test:
push cx
push ax
xor cx, cx
mov fs, cx
dec cx
mov gs, cx
mov cx, 020h
mov ax, [fs:600h]
push ax
.a20_test_wait:
inc ax
mov [fs:600h], ax
wbinvd
cmp ax, [gs:610h]
je .a20_test_wait
pop ax
mov [fs:600h], ax
pop ax
pop cx
ret
loc dw 0
gdt
; Null descriptor.
dw 00000h
; Here we cheat a bit, using a portion of our null descriptor as the GDT
; data loaded into GDTR, saving some bytes.
gdt_main
dw 007FFh
dw 01800h
; CPL0 code segment.
dw 0FFFFh
dw 00000h
dw 09A00h
dw 000CFh
; CPL0 data/stack segment.
dw 0FFFFh
dw 00000h
dw 09200h
dw 000CFh
; Alignement
dw 00000h
idt_main
dw 007FFh
dw 01000h
BITS 32
main32:
; Reload segment registers with our CPL0 data/stack segment.
mov ax, 010h
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov eax, 0B8000h
mov [eax], byte 'X'
mov [eax + 1], byte 007h
jmp $
times 512 - ($ - $$) - 2 db 0
dw 0AA55h
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 11:42 am
by aladdin
Try this
mov eax,cr0
or ax,1
mov cr0,eax ; set PMode to 1
jmp next
next :
; Reload segment registers with our CPL0 data/stack segment.
mov ax, 010h
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esp, 0x9F000 ;you forgot this line
jmp dword addresse_of_your kernel
instead of this
mov eax, 000000011h
mov cr0, eax
jmp dword 008h:main32
hope this will help u
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 11:45 am
by DennisCGc
Hi,
Is it a typo ? AFAIK it should b instead of h...
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 12:37 pm
by chris
I tried what aladdin said, but had no luck. This is what Bochs is saying:
00004279641i[CPU0 ] -----------------------------------
00004279641i[CPU0 ] selector->index*8 + 7 = 15
00004279641i[CPU0 ] gdtr.limit = 0
00004279641i[CPU0 ] fetch_raw_descriptor: GDT: index > limit
00004279641i[CPU0 ] | EAX=00000011 EBX=00000000 ECX=000b0001 EDX=00000064
00004279641i[CPU0 ] | ESP=00009000 EBP=00000000 ESI=00000000 EDI=0000ffe4
00004279641i[CPU0 ] | IOPL=0 NV UP DI PL NZ NA PO NC
00004279641i[CPU0 ] | SEG selector base limit G D
00004279641i[CPU0 ] | SEG sltr(index|ti|rpl) base limit G D
00004279641i[CPU0 ] | DS:7c00( 0000| 0| 0) 0007c000 0000ffff 0 0
00004279641i[CPU0 ] | ES:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | FS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | GS:ffff( 0000| 0| 0) 000ffff0 0000ffff 0 0
00004279641i[CPU0 ] | SS:8000( 0000| 0| 0) 00080000 0000ffff 0 0
00004279641i[CPU0 ] | CS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | EIP=00007c34 (00007c2c)
00004279641i[CPU0 ] | CR0=0x00000011 CR1=0x00000000 CR2=0x00000000
00004279641i[CPU0 ] | CR3=0x00000000 CR4=0x00000000
00004279641i[CPU0 ] -----------------------------------
00004279641e[CPU0 ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetti
ng
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 4:12 pm
by chris
I fixed my GDT pointer (should be "dd 01800h" and not dw ..") and now Bochs outputs:
Code: Select all
00004279641i[CPU0 ] -----------------------------------
00004279641i[CPU0 ] selector->index*8 + 7 = 15
00004279641i[CPU0 ] gdtr.limit = 0
00004279641i[CPU0 ] fetch_raw_descriptor: GDT: index > limit
00004279641i[CPU0 ] | EAX=00000011 EBX=00000000 ECX=000f0001 EDX=00000064
00004279641i[CPU0 ] | ESP=00009000 EBP=00000000 ESI=00000000 EDI=0000ffe4
00004279641i[CPU0 ] | IOPL=0 NV UP DI PL NZ NA PO NC
00004279641i[CPU0 ] | SEG selector base limit G D
00004279641i[CPU0 ] | SEG sltr(index|ti|rpl) base limit G D
00004279641i[CPU0 ] | DS:7c00( 0000| 0| 0) 0007c000 0000ffff 0 0
00004279641i[CPU0 ] | ES:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | FS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | GS:ffff( 0000| 0| 0) 000ffff0 0000ffff 0 0
00004279641i[CPU0 ] | SS:8000( 0000| 0| 0) 00080000 0000ffff 0 0
00004279641i[CPU0 ] | CS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004279641i[CPU0 ] | EIP=00007c34 (00007c2c)
00004279641i[CPU0 ] | CR0=0x00000011 CR1=0x00000000 CR2=0x00000000
00004279641i[CPU0 ] | CR3=0x00000000 CR4=0x00000000
00004279641i[CPU0 ] >> 66
00004279641i[CPU0 ] >> ea
00004279641i[CPU0 ] >> 0e
00004279641i[CPU0 ] >> 01
00004279641i[CPU0 ] >> 00
00004279641i[CPU0 ] >> 00
00004279641i[CPU0 ] >> 08
00004279641i[CPU0 ] >> 00
00004279641i[CPU0 ] >> : opsize jmp 0008:0000010e
00004279641i[CPU0 ] -----------------------------------
00004279641e[CPU0 ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetting
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 5:06 pm
by Dreamsmith
Code: Select all
lgdt [gdt_main]
...
gdt_main
dw 007FFh
dw 01800h
; CPL0 code segment.
dw 0FFFFh
So, your GDT is at address 0xFFFF1800? If not, then this code is in error. Your LIDT code looks fishy too.
Perhaps you meant "dd" instead of "dw"?
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 5:36 pm
by chris
I fixed the IDT problem earlier, I should have mentioned that. I also had forgotten to write the code to move my GDT to 0x1800. Here is the new code, but it still hangs.
Re:Switch to PMode not working
Posted: Sat Sep 18, 2004 5:37 pm
by chris
Code: Select all
ORG 00000h
BITS 16
main:
mov ax, 07C00h
mov ds, ax
mov ax, 08000h
mov ss, ax
mov ax, 09000h
mov sp, ax
; Enable the A20 line.
call .enable_a20
; Reprogram the PIC.
; call .reprogPIC
; Re-enable the keyboard (if it's off)
mov al, 0AEh
mov dx, 064h
out dx, al
cli
; Prevent undefined stuff.
mov di, 01000h
mov cx, 0400h
xor eax, eax
cld
rep stosd
; Move the GDT to 0x1800 linear.
mov si, gdt
mov di, 01800h
mov ecx, 010h
rep movsd
lgdt [gdt_main]
lidt [idt_main]
mov eax, 000000011h
mov cr0, eax
jmp dword 008h:main32
... A20 Stuff
gdt
; Null descriptor.
dw 00000h
; Here we cheat a bit, using a portion of our null descriptor as the GDT
; data loaded into GDTR, saving some bytes.
gdt_main
dw 007FFh
dd 01800h
; CPL0 code segment.
dw 0FFFFh
dw 00000h
dw 09A00h
dw 000CFh
; CPL0 data/stack segment.
dw 0FFFFh
dw 00000h
dw 09200h
dw 000CFh
; Alignement
dw 00000h
idt_main
dw 007FFh
dd 01000h
BITS 32
main32:
; Reload segment registers with our CPL0 data/stack segment.
mov ax, 010h
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esp, 0A0000h
mov eax, 0B8000h
mov [eax], byte 'X'
mov [eax + 1], byte 007h
jmp $
times 512 - ($ - $$) - 2 db 0
dw 0AA55h
Boch's Output:
Code: Select all
00004280688i[CPU0 ] -----------------------------------
00004280688i[CPU0 ] selector->index*8 + 7 = 15
00004280688i[CPU0 ] gdtr.limit = 0
00004280688i[CPU0 ] fetch_raw_descriptor: GDT: index > limit
00004280688i[CPU0 ] | EAX=00000011 EBX=00000000 ECX=00000000 EDX=00000064
00004280688i[CPU0 ] | ESP=00009000 EBP=00000000 ESI=0000014a EDI=00001840
00004280688i[CPU0 ] | IOPL=0 NV UP DI PL ZR NA PE NC
00004280688i[CPU0 ] | SEG selector base limit G D
00004280688i[CPU0 ] | SEG sltr(index|ti|rpl) base limit G D
00004280688i[CPU0 ] | DS:7c00( 0000| 0| 0) 0007c000 0000ffff 0 0
00004280688i[CPU0 ] | ES:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004280688i[CPU0 ] | FS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004280688i[CPU0 ] | GS:ffff( 0000| 0| 0) 000ffff0 0000ffff 0 0
00004280688i[CPU0 ] | SS:8000( 0000| 0| 0) 00080000 0000ffff 0 0
00004280688i[CPU0 ] | CS:0000( 0000| 0| 0) 00000000 0000ffff 0 0
00004280688i[CPU0 ] | EIP=00007c50 (00007c48)
00004280688i[CPU0 ] | CR0=0x00000011 CR1=0x00000000 CR2=0x00000000
00004280688i[CPU0 ] | CR3=0x00000000 CR4=0x00000000
00004280688i[CPU0 ] >> 66
00004280688i[CPU0 ] >> ea
00004280688i[CPU0 ] >> 2a
00004280688i[CPU0 ] >> 01
00004280688i[CPU0 ] >> 00
00004280688i[CPU0 ] >> 00
00004280688i[CPU0 ] >> 08
00004280688i[CPU0 ] >> 00
00004280688i[CPU0 ] >> : opsize jmp 0008:0000012a
00004280688i[CPU0 ] -----------------------------------
00004280688e[CPU0 ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetti
ng
Something must still be wrong with my GDT...
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 8:28 am
by Curufir
Code: Select all
mov ax, 07C00h
mov ds, ax
....
; Move the GDT to 0x1800 linear.
mov si, gdt
mov di, 01800h
mov ecx, 010h
rep movsd
You never bother to set DS to 0, so you've just copied your GDT into a segment starting at 0x7c00. A segment which is wrong for a bootloader anyhow, since it should be 0x7c0 if your ORG is 0. Either way this means you load GDTR with garbage, and then try to use that bad GDTR to load garbage as a selector. At this point Bochs runs home to mommy crying.
In other words.
Old man: This is a warning...not to disturb the Ark of the Covenant.
Jones: What about the height of the staff? Did Belloq get it off of here?
Old man: Yes, it is here...This means six kadams high - 'about seventy-two inches'. Wait! And take back one kadam to honor the Hebrew God whose Ark this is.
Jones: You said their headpiece only had markings on one side. Are you absolutely sure? Belloq's staff is too long.
Sallah and Jones: They're digging in the wrong place! (laughing)
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 10:43 am
by chris
I fixed the 0x7C0 thing, and switched my GDT relocation code to:
Code: Select all
; Move the GDT to 0x1800 linear.
mov si, gdt
mov ax, 0
mov es, ax
mov di, 01800h
mov ecx, 010h
rep movsd
the NASM docs say movsd will move [DS:SI] to [ES:DI]
What is still wrong?
All I see in bochsout.txt is
Code: Select all
00004280691e[CPU0 ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetti
ng
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 11:19 am
by Curufir
This is not good, not good at all. The idea is to turn on the PE bit, not destroy all the others (That includes screwing with the MP bit until you need to).
Try this instead:
Code: Select all
mov eax, cr0
or eax, 1
mov cr0, eax
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 11:33 am
by chris
I'm still getting the same error.
How can I use the Bochs debugger to find where it's happening?
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 11:41 am
by Curufir
This will be jumping to the wrong place.
main32 is a label representing the offset from the start of the text section (Because you're using ORG 0), but that text section has been loaded into the segment starting at 0x7c00. Since when you do the absolute jump the place you want branch to is offset from 0 in memory you need to add 0x7c00 to main32 to reach the right place.
Bochs debugging is just a question of setting some breakpoints and stepping through. The manual makes plenty of sense.
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 11:59 am
by chris
That was it! It works now. Thanks Curufir and everyone else that posted.
Now it's onto filesystem interpretation
.
Re:Switch to PMode not working
Posted: Sun Sep 19, 2004 11:00 pm
by Brendan
Hi,
Curufir wrote:
This is not good, not good at all. The idea is to turn on the PE bit, not destroy all the others (That includes screwing with the MP bit until you need to).
Try this instead:
Code: Select all
mov eax, cr0
or eax, 1
mov cr0, eax
Messing up the other flags isn't such a bad idea - or at least clearing the cache disable flags and task switched flag (some BIOSs leave the caches disabled, and some versions of windows leaves the TS flag set).
As long as the CPU does have an FPU, then
"mov cr0, 000000011h" isn't a bad idea. If it's possible that there is no FPU then I'd use something like:
Code: Select all
mov eax, cr0
and eax,0x00000010
or eax,0x00000001
mov cr0, eax
Cheers,
Brendan