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










share|improve this question






















  • 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 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












  • @MichaelPetch Thank you very much, its work!
    – RonRahamim
    Nov 21 at 20:02















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










share|improve this question






















  • 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 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












  • @MichaelPetch Thank you very much, its work!
    – RonRahamim
    Nov 21 at 20:02













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










share|improve this question













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






share|improve this question













share|improve this question











share|improve this question




share|improve this question










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 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












  • @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






  • 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










  • 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
















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

















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