I tried to use in C “extern void (function_name)” then call that function in my C code. It got to the assembly code that i used the extern on. Problem was it setted up 64 bit mode but when it needed to jump to the long mode it failed. All code is compiled right and other stuff is all correct, only problem is with the jmp
<code>//Problem: jmp 0x08:init_lm
extern void _init_load_lm(void);
void main(void)
{
_init_load_lm();
*(char*)0xb8000 = 'Q';
for(;;);
}
// Assembly code:
bits 32
global _init_load_lm
_init_load_lm:
;Enable PAE
mov eax, cr4
or eax, 1 << 5
mov cr4, eax
;# Optional : Enable global-page mechanism by setting CR0.PGE bit to 1
mov eax, cr4
or eax, 1 << 7
mov cr4, eax
;Load CR3 with PML4 base address
;NB: in some examples online, the address is not offseted as it seems to
;be in the proc datasheet (if you were wondering about this strange thing).
mov eax, 0x1000
mov cr3, eax
;Set LME bit in EFER register (address 0xC0000080)
mov ecx, 0xC0000080 ;operand of 'rdmsr' and 'wrmsr'
rdmsr ;read before pr ne pas écraser le contenu
or eax, 1 << 8 ;eax : operand de wrmsr
wrmsr
;Enable paging by setting CR0.PG bit to 1
mov eax, cr0
or eax, (1 << 31)
mov cr0, eax
;Load 64-bit GDT
lgdt [gdt64_descriptor]
;Jump to code segment in 64-bit GDT
jmp 0x8:init_lm
bits 64
init_lm
mov ax, 0x10
mov fs, ax ;other segments are ignored
mov gs, ax
mov rbp, 0x90000 ;set up stack
mov rsp, rbp
mov al, 'E'
mov ah, 0x0f
mov [0xb8000], ax
ret ; return back to c code where it should be called from
bits 32
GDT64
;null;
dq 0x0
;code
dd 0x0
db 0x0
db 0b10011000
db 0b00100000
db 0x0
;data
dd 0x0
db 0x0
db 0b10010000
db 0b00000000
db 0x0
gdt64_descriptor:
dw $ - GDT64 - 1 ;16-bit size
dd GDT64 ;32-bit start address
// Edit: Page table
[bits 32]
build_page_tables:
;PML4 starts at 0x1000
;il faut laisser la place pour tte la page PML4/PDP/PD ie. 0x1000
;PML4 @ 0x1000
mov eax, 0x2000 ;PDP base address
or eax, 0b11 ;P and R/W bits
mov ebx, 0x1000 ;MPL4 base address
mov [ebx], eax
;PDP @ 0x2000; maps 64Go
mov eax, 0x3000 ;PD base address
mov ebx, 0x2000 ;PDP physical address
mov ecx, 64 ;64 PDP
build_PDP:
or eax, 0b11
mov [ebx], eax
add ebx, 0x8
add eax, 0x1000 ;next PD page base address
loop build_PDP
;PD @ 0x3000 (ends at 0x4000, fits below 0x7c00)
; 1 entry maps a 2MB page, the 1st starts at 0x0
mov eax, 0x0 ;1st page physical base address
mov ebx, 0x3000 ;PD physical base address
mov ecx, 512
build_PD:
or eax, 0b10000011 ;P + R/W + PS (bit for 2MB page)
mov [ebx], eax
add ebx, 0x8
add eax, 0x200000 ;next 2MB physical page
loop build_PD
;(tables end at 0x4000 => fits before Bios boot sector at 0x7c00)
ret
</code>
<code>//Problem: jmp 0x08:init_lm
extern void _init_load_lm(void);
void main(void)
{
_init_load_lm();
*(char*)0xb8000 = 'Q';
for(;;);
}
// Assembly code:
bits 32
global _init_load_lm
_init_load_lm:
;Enable PAE
mov eax, cr4
or eax, 1 << 5
mov cr4, eax
;# Optional : Enable global-page mechanism by setting CR0.PGE bit to 1
mov eax, cr4
or eax, 1 << 7
mov cr4, eax
;Load CR3 with PML4 base address
;NB: in some examples online, the address is not offseted as it seems to
;be in the proc datasheet (if you were wondering about this strange thing).
mov eax, 0x1000
mov cr3, eax
;Set LME bit in EFER register (address 0xC0000080)
mov ecx, 0xC0000080 ;operand of 'rdmsr' and 'wrmsr'
rdmsr ;read before pr ne pas écraser le contenu
or eax, 1 << 8 ;eax : operand de wrmsr
wrmsr
;Enable paging by setting CR0.PG bit to 1
mov eax, cr0
or eax, (1 << 31)
mov cr0, eax
;Load 64-bit GDT
lgdt [gdt64_descriptor]
;Jump to code segment in 64-bit GDT
jmp 0x8:init_lm
bits 64
init_lm
mov ax, 0x10
mov fs, ax ;other segments are ignored
mov gs, ax
mov rbp, 0x90000 ;set up stack
mov rsp, rbp
mov al, 'E'
mov ah, 0x0f
mov [0xb8000], ax
ret ; return back to c code where it should be called from
bits 32
GDT64
;null;
dq 0x0
;code
dd 0x0
db 0x0
db 0b10011000
db 0b00100000
db 0x0
;data
dd 0x0
db 0x0
db 0b10010000
db 0b00000000
db 0x0
gdt64_descriptor:
dw $ - GDT64 - 1 ;16-bit size
dd GDT64 ;32-bit start address
// Edit: Page table
[bits 32]
build_page_tables:
;PML4 starts at 0x1000
;il faut laisser la place pour tte la page PML4/PDP/PD ie. 0x1000
;PML4 @ 0x1000
mov eax, 0x2000 ;PDP base address
or eax, 0b11 ;P and R/W bits
mov ebx, 0x1000 ;MPL4 base address
mov [ebx], eax
;PDP @ 0x2000; maps 64Go
mov eax, 0x3000 ;PD base address
mov ebx, 0x2000 ;PDP physical address
mov ecx, 64 ;64 PDP
build_PDP:
or eax, 0b11
mov [ebx], eax
add ebx, 0x8
add eax, 0x1000 ;next PD page base address
loop build_PDP
;PD @ 0x3000 (ends at 0x4000, fits below 0x7c00)
; 1 entry maps a 2MB page, the 1st starts at 0x0
mov eax, 0x0 ;1st page physical base address
mov ebx, 0x3000 ;PD physical base address
mov ecx, 512
build_PD:
or eax, 0b10000011 ;P + R/W + PS (bit for 2MB page)
mov [ebx], eax
add ebx, 0x8
add eax, 0x200000 ;next 2MB physical page
loop build_PD
;(tables end at 0x4000 => fits before Bios boot sector at 0x7c00)
ret
</code>
//Problem: jmp 0x08:init_lm
extern void _init_load_lm(void);
void main(void)
{
_init_load_lm();
*(char*)0xb8000 = 'Q';
for(;;);
}
// Assembly code:
bits 32
global _init_load_lm
_init_load_lm:
;Enable PAE
mov eax, cr4
or eax, 1 << 5
mov cr4, eax
;# Optional : Enable global-page mechanism by setting CR0.PGE bit to 1
mov eax, cr4
or eax, 1 << 7
mov cr4, eax
;Load CR3 with PML4 base address
;NB: in some examples online, the address is not offseted as it seems to
;be in the proc datasheet (if you were wondering about this strange thing).
mov eax, 0x1000
mov cr3, eax
;Set LME bit in EFER register (address 0xC0000080)
mov ecx, 0xC0000080 ;operand of 'rdmsr' and 'wrmsr'
rdmsr ;read before pr ne pas écraser le contenu
or eax, 1 << 8 ;eax : operand de wrmsr
wrmsr
;Enable paging by setting CR0.PG bit to 1
mov eax, cr0
or eax, (1 << 31)
mov cr0, eax
;Load 64-bit GDT
lgdt [gdt64_descriptor]
;Jump to code segment in 64-bit GDT
jmp 0x8:init_lm
bits 64
init_lm
mov ax, 0x10
mov fs, ax ;other segments are ignored
mov gs, ax
mov rbp, 0x90000 ;set up stack
mov rsp, rbp
mov al, 'E'
mov ah, 0x0f
mov [0xb8000], ax
ret ; return back to c code where it should be called from
bits 32
GDT64
;null;
dq 0x0
;code
dd 0x0
db 0x0
db 0b10011000
db 0b00100000
db 0x0
;data
dd 0x0
db 0x0
db 0b10010000
db 0b00000000
db 0x0
gdt64_descriptor:
dw $ - GDT64 - 1 ;16-bit size
dd GDT64 ;32-bit start address
// Edit: Page table
[bits 32]
build_page_tables:
;PML4 starts at 0x1000
;il faut laisser la place pour tte la page PML4/PDP/PD ie. 0x1000
;PML4 @ 0x1000
mov eax, 0x2000 ;PDP base address
or eax, 0b11 ;P and R/W bits
mov ebx, 0x1000 ;MPL4 base address
mov [ebx], eax
;PDP @ 0x2000; maps 64Go
mov eax, 0x3000 ;PD base address
mov ebx, 0x2000 ;PDP physical address
mov ecx, 64 ;64 PDP
build_PDP:
or eax, 0b11
mov [ebx], eax
add ebx, 0x8
add eax, 0x1000 ;next PD page base address
loop build_PDP
;PD @ 0x3000 (ends at 0x4000, fits below 0x7c00)
; 1 entry maps a 2MB page, the 1st starts at 0x0
mov eax, 0x0 ;1st page physical base address
mov ebx, 0x3000 ;PD physical base address
mov ecx, 512
build_PD:
or eax, 0b10000011 ;P + R/W + PS (bit for 2MB page)
mov [ebx], eax
add ebx, 0x8
add eax, 0x200000 ;next 2MB physical page
loop build_PD
;(tables end at 0x4000 => fits before Bios boot sector at 0x7c00)
ret
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