xchg 2 “Pointers” - function assembly 8086
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I got a mission to build a function thats replace 2 pointers values.
There is my code:
org 100h
jmp main
toSwap1 db 'a'
toSwap2 db 'b'
result dw ?
numToNeg dw -9
string db 'm', 'a', 'g', 's', 'h', 'i', 'm', 'i', 'm', 'v', 'e', 'n', 'e', 'h', 'e', 'n', 'i', 'm' ,0Dh,0Ah,'$'
array db "0000", 0Dh,0Ah, 24h ; line feed return and stop symbol 24h=$ (ASCII).
num1 dw 0xAC45
; There is some vars thats i need for other missions
main:
; Second function: should print b and a - MAIN CODE FOR FUNC ~
push offset toSwap1
push offset toSwap2
call xChange
mov al, toSwap1
call print_al_chr
PRINTN "and"
mov al, toSwap2
call print_al_chr
mov ah, 0
int 16h
ret
xChange proc ; THE FUNC ~
push bp
push ax
push bx
push cx
mov bp, sp
mov bx, [bp + 12]
mov al, [bx]
mov bx, [bp + 10]
mov cx, [bx]
mov [bx], ax
mov bx, [bp + 12]
mov [bx], cx
pop cx
pop bx
pop ax
pop bp
retn 4
xChange endp
Now the problem is that the value of the second var (thats should print 'a' at the end of the function got reset)....
picture:
enter image description here
function pointers stack x86-16 emu8086
asked Nov 21 at 19:27
RonRahamim
12
add a comment |
up vote
0
down vote
favorite
I got a mission to build a function thats replace 2 pointers values.
There is my code:
org 100h
jmp main
toSwap1 db 'a'
toSwap2 db 'b'
result dw ?
numToNeg dw -9
string db 'm', 'a', 'g', 's', 'h', 'i', 'm', 'i', 'm', 'v', 'e', 'n', 'e', 'h', 'e', 'n', 'i', 'm' ,0Dh,0Ah,'$'
array db "0000", 0Dh,0Ah, 24h ; line feed return and stop symbol 24h=$ (ASCII).
num1 dw 0xAC45
; There is some vars thats i need for other missions
main:
; Second function: should print b and a - MAIN CODE FOR FUNC ~
push offset toSwap1
push offset toSwap2
call xChange
mov al, toSwap1
call print_al_chr
PRINTN "and"
mov al, toSwap2
call print_al_chr
mov ah, 0
int 16h
ret
xChange proc ; THE FUNC ~
push bp
push ax
push bx
push cx
mov bp, sp
mov bx, [bp + 12]
mov al, [bx]
mov bx, [bp + 10]
mov cx, [bx]
mov [bx], ax
mov bx, [bp + 12]
mov [bx], cx
pop cx
pop bx
pop ax
pop bp
retn 4
xChange endp
Now the problem is that the value of the second var (thats should print 'a' at the end of the function got reset)....
picture:
enter image description here
function pointers stack x86-16 emu8086
asked Nov 21 at 19:27
RonRahamim
12
Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
1
You're loadingal(which matched yourdbdata size), but then you're loadingcxand storingax(16 bits).
– Peter Cordes
Nov 21 at 19:33
Because yourxChangeproc writes 16-bits of data (word) into the destination, rather than a byte.mov [bx], axshould bemov [bx], alandmov [bx], cxshould bemov [bx], cl. As well it is often more convenient to putmov bp,spright afterpush bp. This way the first parameter will always be at bp+4 (assuming the return address is near)
– Michael Petch
Nov 21 at 19:43
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
I got a mission to build a function thats replace 2 pointers values.
There is my code:
org 100h
jmp main
toSwap1 db 'a'
toSwap2 db 'b'
result dw ?
numToNeg dw -9
string db 'm', 'a', 'g', 's', 'h', 'i', 'm', 'i', 'm', 'v', 'e', 'n', 'e', 'h', 'e', 'n', 'i', 'm' ,0Dh,0Ah,'$'
array db "0000", 0Dh,0Ah, 24h ; line feed return and stop symbol 24h=$ (ASCII).
num1 dw 0xAC45
; There is some vars thats i need for other missions
main:
; Second function: should print b and a - MAIN CODE FOR FUNC ~
push offset toSwap1
push offset toSwap2
call xChange
mov al, toSwap1
call print_al_chr
PRINTN "and"
mov al, toSwap2
call print_al_chr
mov ah, 0
int 16h
ret
xChange proc ; THE FUNC ~
push bp
push ax
push bx
push cx
mov bp, sp
mov bx, [bp + 12]
mov al, [bx]
mov bx, [bp + 10]
mov cx, [bx]
mov [bx], ax
mov bx, [bp + 12]
mov [bx], cx
pop cx
pop bx
pop ax
pop bp
retn 4
xChange endp
Now the problem is that the value of the second var (thats should print 'a' at the end of the function got reset)....
picture:
enter image description here
function pointers stack x86-16 emu8086
asked Nov 21 at 19:27
RonRahamim
12
I got a mission to build a function thats replace 2 pointers values.
There is my code:
org 100h
jmp main
toSwap1 db 'a'
toSwap2 db 'b'
result dw ?
numToNeg dw -9
string db 'm', 'a', 'g', 's', 'h', 'i', 'm', 'i', 'm', 'v', 'e', 'n', 'e', 'h', 'e', 'n', 'i', 'm' ,0Dh,0Ah,'$'
array db "0000", 0Dh,0Ah, 24h ; line feed return and stop symbol 24h=$ (ASCII).
num1 dw 0xAC45
; There is some vars thats i need for other missions
main:
; Second function: should print b and a - MAIN CODE FOR FUNC ~
push offset toSwap1
push offset toSwap2
call xChange
mov al, toSwap1
call print_al_chr
PRINTN "and"
mov al, toSwap2
call print_al_chr
mov ah, 0
int 16h
ret
xChange proc ; THE FUNC ~
push bp
push ax
push bx
push cx
mov bp, sp
mov bx, [bp + 12]
mov al, [bx]
mov bx, [bp + 10]
mov cx, [bx]
mov [bx], ax
mov bx, [bp + 12]
mov [bx], cx
pop cx
pop bx
pop ax
pop bp
retn 4
xChange endp
Now the problem is that the value of the second var (thats should print 'a' at the end of the function got reset)....
picture:
enter image description here
function pointers stack x86-16 emu8086
function pointers stack x86-16 emu8086
asked Nov 21 at 19:27
RonRahamim
12
asked Nov 21 at 19:27
RonRahamim
12
asked Nov 21 at 19:27
RonRahamim
12
asked Nov 21 at 19:27
RonRahamim
12
asked Nov 21 at 19:27
RonRahamim
12
12
Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
1
You're loadingal(which matched yourdbdata size), but then you're loadingcxand storingax(16 bits).
– Peter Cordes
Nov 21 at 19:33
Because yourxChangeproc writes 16-bits of data (word) into the destination, rather than a byte.mov [bx], axshould bemov [bx], alandmov [bx], cxshould bemov [bx], cl. As well it is often more convenient to putmov bp,spright afterpush bp. This way the first parameter will always be at bp+4 (assuming the return address is near)
– Michael Petch
Nov 21 at 19:43
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02
add a comment |
Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
1
You're loadingal(which matched yourdbdata size), but then you're loadingcxand storingax(16 bits).
– Peter Cordes
Nov 21 at 19:33
Because yourxChangeproc writes 16-bits of data (word) into the destination, rather than a byte.mov [bx], axshould bemov [bx], alandmov [bx], cxshould bemov [bx], cl. As well it is often more convenient to putmov bp,spright afterpush bp. This way the first parameter will always be at bp+4 (assuming the return address is near)
– Michael Petch
Nov 21 at 19:43
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02
Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
1
1
You're loading
al (which matched your db data size), but then you're loading cx and storing ax (16 bits).– Peter Cordes
Nov 21 at 19:33
You're loading
al (which matched your db data size), but then you're loading cx and storing ax (16 bits).– Peter Cordes
Nov 21 at 19:33
Because your
xChange proc writes 16-bits of data (word) into the destination, rather than a byte. mov [bx], ax should be mov [bx], al and mov [bx], cx should be mov [bx], cl . As well it is often more convenient to put mov bp,sp right after push bp. This way the first parameter will always be at bp+4 (assuming the return address is near)– Michael Petch
Nov 21 at 19:43
Because your
xChange proc writes 16-bits of data (word) into the destination, rather than a byte. mov [bx], ax should be mov [bx], al and mov [bx], cx should be mov [bx], cl . As well it is often more convenient to put mov bp,sp right after push bp. This way the first parameter will always be at bp+4 (assuming the return address is near)– Michael Petch
Nov 21 at 19:43
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02
add a comment |
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Explain in words what the problem is, not just with a picture of your IDE with a bunch of windows. Minimal, Complete, and Verifiable example.
– Peter Cordes
Nov 21 at 19:32
1
You're loading
al(which matched yourdbdata size), but then you're loadingcxand storingax(16 bits).– Peter Cordes
Nov 21 at 19:33
Because your
xChangeproc writes 16-bits of data (word) into the destination, rather than a byte.mov [bx], axshould bemov [bx], alandmov [bx], cxshould bemov [bx], cl. As well it is often more convenient to putmov bp,spright afterpush bp. This way the first parameter will always be at bp+4 (assuming the return address is near)– Michael Petch
Nov 21 at 19:43
@MichaelPetch Thank you very much, its work!
– RonRahamim
Nov 21 at 20:02