问题
So as far as I can tell, the exit code returned from r0
only uses the lowest 8 bits of this register. How wouuld I return a value higher than 8 bits?
Here is the ARMv7 code:
@ looping.s
@ calculates sum of integers from 1 to 100
.text
.balign 4
.global main
main:
MOV r1, #0 @ r1 = 0 as sum
MOV r2, #0 @ r2 = 0 as counter
loop:
ADD r2, r2, #1 @ counter = counter + 1
ADD r1, r1, r2 @ sum = sum + counter
CMP r2, #100 @ counter - 100
BLT loop @ if counter < 100 go to start of loop
MOV r0, r1 @ Store sum in r0
BX lr @ Return summation result to OS
回答1:
The exit status of a process is 8 bits in size. It is not possible to return a larger exit status by normal means. If you want to output a number larger than 255, you could for example print it to stdout (file descriptor 1) with a write
system call.
回答2:
You shouldn't be using the main()
function to perform calculations. In general, functions are not restricted to 8-bit return values, so give your actual function a different name and return a larger integer in R0. Invoke your function from inside main()
and then do whatever you need to do with the return value, perhaps print it to the console.
来源:https://stackoverflow.com/questions/58457878/how-to-return-a-number-larger-than-8-bits-from-main