如何在Apple Silicon (aarch64 macos)汇编中使用_scanf来读取用户输入？

huangapple
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英文:

How to use _scanf in Apple Silicon (aarch64 macos) assembly to read in user input?

问题

I'm new to assembly programming, but I've been figuring a lot out by googling and trial and error. I'm trying to write a simple program that prompts the user to enter a number (with _printf), then reads in and saves that number (_scanf), then prints out a message using the stored number (_printf).

I was able to get the _printf code to work under aarch64 (Apple Silicon) assembly, but no matter what I do, I cannot seem to get _scanf to work. I have looked through the ARM Developer docs, looked at the HelloSilicon github page, and googled for hours, and I cannot come up with anything that works.

In my code (included below), if I comment out the "read_from_keyboard" branch in the following code, the printf functions work just fine. But when I include the "read_from_keyboard" code, I get a "Segmentation fault: 11" error.

Where is my mistake?

  1. .global main
  2. .align 4
  4. main:
  5.     // PRINT MESSAGE
  6.     ADRP X0, message@PAGE
  7.     ADD X0, X0, message@PAGEOFF
  8.     BL _printf
  10. //    BL read_from_keyboad
  12.     // READ NUMBER FROM DATA AND MOVE TO STACK FOR PRINTING
  13.     ADRP X10, num@PAGE
  14.     ADD X10, X10, num@PAGEOFF
  15.     LDR X1, [X10]
  16.     STR X1, [SP, #-16]!
  18.     // LOAD THE PRINTF FORMATTED MESSAGE
  19.     ADRP X0, output_format@PAGE
  20.     ADD X0, X0, output_format@PAGEOFF
  22. end:
  23.     BL _printf
  24.     mov X16, #1
  25.     svc 0
  27. read_from_keyboard:
  28.     ADRP X0, input_format@PAGE
  29.     ADD X0, X0, input_format@PAGEOFF
  31.     ADRP X11, num@PAGE
  32.     ADD X11, X11, num@PAGEOFF
  33.     BL _scanf
  35.     ret
  37. .data
  38. .balign 4
  39. message:    .asciz "What is your favorite number?\n"
  40. .balign 4
  41. num:    .word 32
  42. .balign 4
  43. input_format:   .asciz "%d"
  44. .balign 4
  45. output_format:  .asciz "Your favorite number is %d \n"

(Note: Code sections are provided as requested. Please note that this code may not run properly due to potential issues with the assembly code itself or system-specific configurations.)

英文:

I'm new to assembly programming, but I've been figuring a lot out by googling and trial and error. I'm trying to write a simple program that prompts the user to enter a number (with _printf), then reads in and saves that number (_scanf), then prints out a message using the stored number (_printf).

I was able to get the _printf code to work under aarch64 (Apple Silicon) assembly, but no matter what I do, I cannot seem to get _scanf to work. I have looked through the ARM Developer docs, looked at the HelloSilicon github page, and googled for hours, and I cannot come up with anything that works.

In my code (included below), if I comment out the "read_from_keyboard" branch in the following code, the printf functions work just fine. But when I include the "read_from_keyboard" code, I get a "Segmentation fault: 11" error.

Where is my mistake?

  1. .global main
  2. .align 4
  4. main:
  5. 	// PRINT MESSAGE
  6. 	ADRP	X0, message@PAGE
  7. 	ADD	X0, X0, message@PAGEOFF
  8. 	BL	_printf
  10. //	BL read_from_keyboad
  12. 	// READ NUMBER FROM DATA AND MOVE TO STACK FOR PRINTING
  13. 	ADRP	X10, num@PAGE
  14. 	ADD	X10, X10, num@PAGEOFF
  15. 	LDR X1, [X10]
  16. 	STR	X1, [SP, #-16]!
  18. 	// LOAD THE PRINTF FORMATTED MESSAGE
  19. 	ADRP	X0, output_format@PAGE
  20. 	ADD	X0, X0, output_format@PAGEOFF
  22. end:
  23. 	BL	_printf
  24. 	mov	X16, #1
  25. 	svc	0
  27. read_from_keyboard:
  28. 	ADRP	X0, input_format@PAGE
  29. 	ADD	X0, X0, input_format@PAGEOFF
  31. 	ADRP	X11, num@PAGE
  32. 	ADD	X11, X11, num@PAGEOFF
  33. 	BL _scanf
  35. 	ret
  38. .data
  39. .balign 4
  40. message:	.asciz "What is your favorite number?\n"
  41. .balign 4
  42. num:	.word 32
  43. .balign 4
  44. input_format:	.asciz "%d"
  45. .balign 4
  46. output_format:	.asciz "Your favorite number is %d \n"

答案1

得分: 0

在对 _printf 的调用中，你的可变参数位于 [sp]。在对 _scanf 的调用中，你将它放在了 x11 中。为什么这样做？只需执行与 _printf 中相同的操作 str xN, [sp, #-16]!，这将修复你的段错误。

另外，你还需要为 read_from_keyboard 创建一个堆栈帧。bl _scanf 会破坏 x30，因此接下来的 ret 会陷入无限循环。

修复这两个问题，你的代码就可以正常工作：

  1. .global _main
  2. .align 4
  4. _main:
  5.     // 打印消息
  6.     ADRP    X0, message@PAGE
  7.     ADD X0, X0, message@PAGEOFF
  8.     BL  _printf
  10.     BL read_from_keyboard
  12.     // 从数据中读取数字并移到堆栈以进行打印
  13.     ADRP    X10, num@PAGE
  14.     ADD X10, X10, num@PAGEOFF
  15.     LDR X1, [X10]
  16.     STR X1, [SP, #-16]!
  18.     // 载入 printf 格式化消息
  19.     ADRP    X0, output_format@PAGE
  20.     ADD X0, X0, output_format@PAGEOFF
  22. end:
  23.     BL  _printf
  24.     mov X16, #1
  25.     svc 0
  27. read_from_keyboard:
  28.     STP X29, X30, [SP, #-16]!
  30.     ADRP    X0, input_format@PAGE
  31.     ADD X0, X0, input_format@PAGEOFF
  32.     ADRP    X11, num@PAGE
  33.     ADD X11, X11, num@PAGEOFF
  34.     STR X11, [SP, #-16]!
  35.     BL _scanf
  36.     ADD SP, SP, #16
  38.     LDP X29, X30, [SP], #16
  39.     ret
  41. .data
  42. .balign 4
  43. message:    .asciz "What is your favorite number?\n"
  44. .balign 4
  45. num:    .word 32
  46. .balign 4
  47. input_format:   .asciz "%d"
  48. .balign 4
  49. output_format:  .asciz "Your favorite number is %d \n"

请注意，我只翻译了代码中的注释和字符串部分，而没有进行其他更改。

英文:

On the call to _printf, your variadic arg is in [sp]. On the call to _scanf, you put it in x11. Why? Just do the same str xN, [sp, #-16]! that you do on _printf, that'll fix your segfault.

In addition though, you also need a stack frame for read_from_keyboard. The bl _scanf clobbers x30, so the following ret would just get stuck in an infinite loop.

Fix these two issues and your code works:

  1. .global _main
  2. .align 4
  4. _main:
  5.     // PRINT MESSAGE
  6.     ADRP    X0, message@PAGE
  7.     ADD X0, X0, message@PAGEOFF
  8.     BL  _printf
  10.     BL read_from_keyboard
  12.     // READ NUMBER FROM DATA AND MOVE TO STACK FOR PRINTING
  13.     ADRP    X10, num@PAGE
  14.     ADD X10, X10, num@PAGEOFF
  15.     LDR X1, [X10]
  16.     STR X1, [SP, #-16]!
  18.     // LOAD THE PRINTF FORMATTED MESSAGE
  19.     ADRP    X0, output_format@PAGE
  20.     ADD X0, X0, output_format@PAGEOFF
  22. end:
  23.     BL  _printf
  24.     mov X16, #1
  25.     svc 0
  27. read_from_keyboard:
  28.     STP X29, X30, [SP, #-16]!
  30.     ADRP    X0, input_format@PAGE
  31.     ADD X0, X0, input_format@PAGEOFF
  32.     ADRP    X11, num@PAGE
  33.     ADD X11, X11, num@PAGEOFF
  34.     STR X11, [SP, #-16]!
  35.     BL _scanf
  36.     ADD SP, SP, #16
  38.     LDP X29, X30, [SP], #16
  39.     ret
  42. .data
  43. .balign 4
  44. message:    .asciz "What is your favorite number?\n"
  45. .balign 4
  46. num:    .word 32
  47. .balign 4
  48. input_format:   .asciz "%d"
  49. .balign 4
  50. output_format:  .asciz "Your favorite number is %d \n"

huangapple
  • 本文由 发表于 2023年1月9日 16:42:18
  • 转载请务必保留本文链接：https://go.coder-hub.com/75054828.html
  • arm64
  • assembly
  • macos
  • scanf
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