【发布时间】：2015-02-28 13:35:43
【问题描述】：
我正在做一个项目。在 64 位 NASM 中。我必须将十进制转换为二进制，将二进制转换为十进制。
当我调用 printf 时，调试后不断出现分段错误。
extern printf
section .bss
decsave: resd 2 ; stores dec->bin conversion
binsave: resd 1
section .data ; preset constants, writeable
dec1: db '1','2','4','.','3','7','5',0
bin1: dq 01010110110101B ; 10101101.10101 note where binary point should be
ten: dq 10
debug: db "debug 124 is %ld", 10, 0
section .text ; instructions, code segment
global main ; for gcc standard linking
main: ; label
push rbp ; save rbp
;parse and convert integer portion of dec->bin
mov rax,0 ; accumulate value here
mov al,[dec1] ; get first ASCII digit
sub al,48 ; convert ASCII digit to binary
mov rbx,0 ; clear register (upper part)
mov bl,[dec1+1] ; get next ASCII digit
sub rbx,48 ; convert ASCII digit to binary
imul rax,10 ; ignore rdx
add rax,rbx ; increment accumulator
mov rbx,0
mov bl,[dec1+2]
sub rbx,48
imul rax,10
add rax,rbx
mov [decsave],rax ; save decimal portion
mov rdi, debug
mov rsi, [decsave]
mov rax,0
call printf
; return using c-style pops to return stack to correct position
; and registers to correct content
pop rbp
mov rax,0
ret ; return
; print the bits in decsave:
section .bss
abits: resb 17 ; 16 characters & zero terminator
section .data
fmts: db "%s",0
section .text
; shift decimal portion into abits as ascii
mov rax,[decsave] ; restore rax to dec. portion
mov rcx,8 ; for printing 1st 8 bits
loop3: mov rdx,0 ; clear rdx ready for a bit
shld rdx,rax,1 ; top bit of rax into rdx
add rdx,48 ; make it ASCII
mov [abits+rcx-1],dl ; store character
ror rax,1 ; next bit into top of rax
loop loop3 ; decrement rcx, jump non zero
mov byte [abits+7],'.' ; end of dec. portion string
mov byte [abits+8],0 ; end of "C" string
push qword abits ; string to print
push qword fmts ; "%s"
call printf
add rsp,8
mov rax,[decsave+16] ; increment to fractional portion
mov rcx,16 ; for printing 3 bits as required in the directions
loop4: mov rdx,0 ; clear rdx ready for a bit
shld rdx,rax,1 ; top bit of rax into rdx
add rdx,48 ; make it ASCII
mov [abits+rcx-1],dl ; store character
ror rax,1 ; next bit into top of rax
loop loop4 ; decrement rcx, jump non zero
mov byte [abits+3],10 ; end of "C" string at 3 places
mov byte [abits+4],0 ; end of "C" string
push qword abits ; string to print
push qword fmts ; "%s"
call printf
add rsp,8
还有其他方法可以解决吗？
谢谢。
【问题讨论】：
-
根据 x86-64 调用约定，varags 函数（而
printf为一）期望用于在AL中传递的 sse 寄存器的数量。长话短说，您需要在call printf之前将AL归零。