【发布时间】：2020-10-11 18:33:06
【问题描述】：
我正在尝试在 ARM 汇编中构建一个基本的 4 函数计算器。我们必须使用 Push 和 Pop，这 4 个函数中的每一个都必须是自己的子程序。
由于某种原因，我无法将值传递给子例程。教授说我们不需要使用堆栈帧或帧指针，我想这很好，但我不知道为什么这不起作用。我在正确的地方使用了 PUSH 命令吗？我是否只需要推动 LR，如果是，我应该如何以及在哪里放置它？
如果格式混乱，也很抱歉。我不知道如何在 Stack Overflow 中做任何事情。
.equ READERROR, 0 @Used to check for scanf read error.
.global main @ Have to use main because of C library uses.
main:
@*******************
begin:
@*******************
@ Welcome message.
ldr r0, =strInputPrompt @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
ldr r0, =inputPrompt1 @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
ldr r0, =numInputPattern @ Setup to read in one number.
ldr r1, =intInput @ load r1 with the address of where theinput value will be stored.
bl scanf @ scan the keyboard
cmp r0, #READERROR @ Check for a read error.
beq readerror @ If there was a read error go handle it.
ldr r3, =intInput @ load intInput into r3
ldr r3, [r3] @ Read the contents of intInput and store in r3
mov r2, #-1 @ load -1 into r2
cmp r3, r2 @ is the value entered less than or equal to -1?
ble invalidnums @ if yes, print invalid message
ldr r0, =inputPrompt2 @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
ldr r0, =numInputPattern @ Setup to read in one number.
ldr r1, =intInput2 @ load r1 with the address of where theinput value will be stored.
bl scanf @ scan the keyboard
cmp r0, #READERROR @ Check for a read error.
ldr r4, =intInput @ load intInput into r4
ldr r4, [r4] @ Read the contents of intInput and store in r4
mov r3, #-1 @ load -1 into r2
cmp r4, r3 @ is the value entered less than or equal to -1?
ble invalidnums @ if yes, print invalid message
@blt again @ if invalid return value, ask for another attempt
@mov r1, r0
@ldr r0, =answer
@bl printf @ print the answer
@b again @ ask another attempt
@*******************
get_op:
@*******************
ldr r0, =inputPrompt3 @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
ldr r0, =charInputPattern @ Setup to read in one number.
ldr r1, =charInput @ load r1 with the address of where theinput value will be stored.
bl scanf @ scan the keyboard
cmp r0, #READERROR @ Check for a read error.
ldr r5, =charInput @ load charInput into r5
ldr r5, [r5] @ Read the contents of charInput and store in r5
push {r3,r4}
cmp r5, #'+' @ did user enter +?
beq addTest @ if yes, go to addTest
cmp r5, #'-' @ did user enter -?
beq subTest @ if yes, go to subTest
cmp r5, #'*' @ did user enter *?
beq multTest @ if yes, go to multTest
cmp r5, #'/' @ did user enter /?
beq divTest @ if yes, go to divTest
b begin @ back to beginning of program
@*******************
addTest:
@*******************
ldr r0, =addOpt @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
bl addCalc
pop {r0}
mov r1, r0
ldr r0, =answer
bl printf
@*******************
subTest:
@*******************
ldr r0, =subOpt @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
bl subCalc
pop {r0}
mov r1, r0
ldr r0, =answer
bl printf
@*******************
multTest:
@*******************
ldr r0, =multOpt @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
bl multCalc
pop {r0}
@*******************
divTest:
@*******************
ldr r0, =divOpt @ Put the address of my string into the first parameter
bl printf @ Call the C printf to display input prompt.
bl divCalc
pop {r0}
@***********
addCalc:
@***********
pop {r5,r6}
add r6, r5, r6
@cmp r6, #0 @ test if upper word is non-zero (for overflow)
@vs overflow
@movgt r7, #-1 @ if overflow, load -1 as a result
@asrle r7, #1 @ if not, divide by 2
@blgt overflow @ if overflow, print overflow
@mov r0, r7
push {r6}
bx lr @ return
@***********
subCalc:
@***********
pop {r5,r6}
subs r6, r5, r6 @ subtract r5-r6 and store in r6
@cmp r6, #0 @ test if upper word is non-zero (for overflow)
@vs overflow
@movgt r7, #-1 @ if overflow, load -1 as a result
@asrle r7, #1 @ if not, divide by 2
@blgt overflow @ if overflow, print overflow
@mov r0, r7
push {r6} @ return
bx lr
@***********
multCalc:
@***********
mov r6, #0
umull r7, r6, r4, r5 @ 64-bit multiplication
@cmp r6, #0 @ test if upper word is non-zero (for overflow)
@vs overflow
@movgt r7, #-1 @ if overflow, load -1 as a result
@asrle r7, #1 @ if not, divide by 2
@blgt overflow @ if overflow, print overflow
mov r0, r7
push {r6}
bx lr @ return
@***********
divCalc:
@***********
mov r6, #0
bl divLoop
@cmp r6, #0 @ test if upper word is non-zero (for overflow)
@vs overflow
@movgt r7, #-1 @ if overflow, load -1 as a result
@asrle r7, #1 @ if not, divide by 2
@blgt overflow @ if overflow, print overflow
@mov r0, r7
push {r6}
bx lr @ return
@***********
divLoop:
@***********
subs r4, r4, r5 @ r4-r5 and store in r4. this will be remainder
adds r7, r7, #1 @ increment by 1. this is how many times r4 has been divided
cmp r4, r5 @ if r4 < r5 return to divCalc
bx lr
@***********
overflow:
@***********
push {lr}
push {fp}
mov fp, sp @ create stack frame
ldr r0, =overstr @ load overflow string
bl printf @ print overflow string
pop {fp} @ restore stack frame
pop {pc} @ return
@***********
returnInput:
@***********
@ reset stack
add sp, #4 @ restore stack
pop {fp} @ restore frame
pop {pc} @ return
@***********
again:
@***********
ldr r0, =againstr
bl printf @ print againstr
sub sp, #1 @ allocate space for one char
mov r1, sp
ldr r0, =charInputPattern
bl scanf @ scan the keyboard
mov r0, #0
ldrsb r0, [sp], #4 @ load char and restore stack
cmp r0, #'y' @ compare to 'y'
beq begin @ if y, go back to the beginning
cmp r0, #'n' @ compare to 'n'
beq myexit @ if n, exit the program
b again @ else, try again
@***********
invalidnums:
@***********
ldr r1, [fp, #8]
mov r0, #-1
str r0, [r1] @set the inputted value to -1
sub sp, #100 @ allocate space for a 100-character string
ldr r0, =charInputPattern
mov r1, sp
bl scanf @ scan the keyboard
add sp, #100 @ restore stack
@*******************
myexit:
@*******************
@ End of my code. Force the exit and return control to OS
mov r7, #0x01 @SVC call to exit
svc 0 @Make the system call.
@***********
readerror:
@***********
@ Got a read error from the scanf routine. Clear out the input buffer then
@ branch back for the user to enter a value.
@ Since an invalid entry was made we now have to clear out the input buffer by
@ reading with this format %[^\n] which will read the buffer until the user
@ presses the CR.
ldr r0, =strInputPattern
ldr r1, =strInputError @ Put address into r1 for read.
bl scanf @ scan the keyboard.
@ Not going to do anything with the input. This just cleans up the input buffer.
@ The input buffer should now be clear so get another input.
b again
.data
@ Declare the strings and data needed
.balign 4
strInputPrompt: .asciz "Hello. Enter 2 non-negative integers and an operation (+, -, *, or /) and I
will calculate the answer. \n"
.balign 4
inputPrompt1: .asciz "Enter first non-negative integer: \n "
.balign 4
inputPrompt2: .asciz "Enter second non-negative integer: \n "
.balign 4
inputPrompt3: .asciz "Enter the operation (+, -, *, or /): \n "
.balign 4
addOpt: .asciz "Addition \n "
.balign 4
subOpt: .asciz "Subtraction \n "
.balign 4
multOpt: .asciz "Multiplication \n "
.balign 4
divOpt: .asciz "Division \n "
.balign 4
answer: .asciz "The answer is: \n"
.balign 4
overstr: .asciz "Overflow \n"
.balign 4
againstr: .asciz "Try another calculation? \n"
.balign 4
nl: .asciz "\n"
.balign 4
invalidStr: .asciz "Invalid input, try again \n"
@ Format pattern for scanf call.
.balign 4
numInputPattern: .asciz "%d" @ integer format for read.
.balign 4
charInputPattern: .asciz "%s" @ character format for read.
.balign 4
intInput: .word 0 @ Location used to store the user input.
.balign 4
intInput2: .word 0 @ Location used to store the user input.
.balign 4
charInput: .word 0 @ Location used to store the user input.
.balign 4
strInputPattern: .asciz "%[^\n]" @ Used to clear the input buffer for invalid input.
.balign 4
strInputError: .skip 100*4 @ User to clear the input buffer for invalid input.
@ Let the assembler know these are the C library functions.
.global printf
.global scanf
@end of code and end of file. Leave a blank line after this.
`
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