这是我来自wiki的NASM代码。我在MacOS 10.12.6中使用以下命令编译它。
nasm -f macho64 -o echo.o echo.asm
ld echo.o -e _start -o echo
我用：
运行程序./echo
我发现out字符串不打印。我使用lldb来调试它，发现传递给syscall的地址不是out字符串的实际地址。（实际地址是0x2013，传递的地址是0x2026）所以它打印一个空字符串。 NASM的版本是2.13.02。有人可以解释为什么会发生这种情况以及如何解决这个问题吗？
global _start
section .data
query_string: db "Enter a character: "
query_string_len: equ $ - query_string
out_string: db "You have input: "
out_string_len: equ $ - out_string
section .bss
in_char: resw 4
section .text
_start:
mov rax, 0x2000004 ; put the write-system-call-code into register rax
mov rdi, 1 ; tell kernel to use stdout
mov rsi, query_string ; rsi is where the kernel expects to find the address of the message
mov rdx, query_string_len ; and rdx is where the kernel expects to find the length of the message
syscall
; read in the character
mov rax, 0x2000003 ; read system call
mov rdi, 0 ; stdin
mov rsi, in_char ; address for storage, declared in section .bss
mov rdx, 2 ; get 2 bytes from the kernel's buffer (one for the carriage return)
syscall
; show user the output
mov rax, 0x2000004 ; write system call
mov rdi, 1 ; stdout
mov rsi, out_string
mov rdx, out_string_len
syscall
mov rax, 0x2000004 ; write system call
mov rdi, 1 ; stdout
mov rsi, in_char
mov rdx, 2 ; the second byte is to apply the carriage return expected in the string
syscall
; exit system call
mov rax, 0x2000001 ; exit system call
xor rdi, rdi
syscall