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我試圖在下面的ARM程序中填充我的數組a，程序運行時沒有問題，但使用i值填充它，但我現在試圖用用戶輸入填充索引。我實現的_scanf沒有任何問題，因爲我之前在許多程序中使用它（在很多其他程序中調用它），但在此程序中，它假設在10點停止，但不是。它繼續前進，我不知道問題出在哪裏。ARM：如何從用戶輸入中正確填充數組？
.global main
.func main
main:
MOV R3, #0 @ initialze index variable
BL writeloop @ call write function
BL readloop @call read function (prints a)
writeloop:
CMP R3, #10 @ check to see if we are done iterating
BEQ writedone @ exit loop if done
LDR R1, =a @ get address of a
LSL R2, R3, #2 @ multiply index*4 to get array offset
ADD R2, R1, R2 @ R2 now has the element address
BL _scanf
MOV R4,R0
STR R4, [R2] @ write input to a[i]
ADD R3, R3, #1 @ increment index
B writeloop @ branch to next loop iteration
writedone:
MOV R3, #0 @ initialze index variable
readloop:
CMP R3, #10 @ check to see if we are done iterating
BEQ readdone @ exit loop if done
LDR R1, =a @ get address of a
LSL R2, R3, #2 @ multiply index*4 to get array offset
ADD R2, R1, R2 @ R2 now has the element address
LDR R1, [R2] @ read the array at address
PUSH {R3} @ backup register before printf
PUSH {R1} @ backup register before printf
PUSH {R2} @ backup register before printf
MOV R2, R1 @ move array value to R2 for printf
MOV R1, R3 @ move array index to R1 for printf
BL _printf @ branch to print procedure with return
POP {R2} @ restore register
POP {R1} @ restore register
POP {R3} @ restore register
ADD R3, R3, #1 @ increment index
B readloop @ branch to next loop iteration
readdone:
MOV R3,#0 @reset counter (i)
_scanf:
PUSH {LR} @ store the return address
PUSH {R1} @ backup regsiter value
LDR R0, =format_str @ R0 contains address of format string
SUB SP, SP, #4 @ make room on stack
MOV R1, SP @ move SP to R1 to store entry on stack
BL scanf @ call scanf
LDR R0, [SP] @ load value at SP into R0
ADD SP, SP, #4 @ remove value from stack
POP {R1} @ restore register value
POP {PC} @ restore the stack pointer and return
_exit:
MOV R7, #4 @ write syscall, 4
MOV R0, #1 @ output stream to monitor, 1
MOV R2, #21 @ print string length
LDR R1, =exit_str @ string at label exit_str:
SWI 0 @ execute syscall
MOV R7, #1 @ terminate syscall, 1
SWI 0 @ execute syscall
_printf:
PUSH {LR} @ store the return address
LDR R0, =printf_str @ R0 contains formatted string address
BL printf @ call printf
POP {PC} @ restore the stack pointer and return
.data
format_str: .asciz "%d"
.balign 4
a: .skip 40
printf_str: .asciz "a[%d] = %d\n"
exit_str: .ascii "Terminating program.\n"
'R3'是主叫方保存的寄存器，所以'BL scanf'會破壞它的價值。 PS：學習使用調試器。 – Jester
_scanf返回值應該存儲在R0中，R3與它有什麼關係？ – aero
您使用'R3'作爲計數器，但由於它是根據ABI調用者保存的，因此'BL scanf'可能會根據它的喜好進行更改。 – Jester