;\ 注释后的指令不执行?NASM 评论中的反斜杠有什么特别之处? [英] Instructions after a ;\ comment don't execute? What's special about backslash in comments in NASM?
问题描述
我在 ASM 中编写了一个 ASCII 到十进制转换器，经过编辑，它没有添加到 rax，这导致了无限循环.GDB 表示 rax 不接受任何数字，即使从内存和其他寄存器中移出也是如此.
I was programming an ASCII to decimal converter in ASM and after an edit, it just didn't add to rax, this caused an infinite loop. GDB says that rax wasn't accepting ANY numbers, even when moved from memory and other registers.
我试过用 mov 把东西移到 rax 中，我也试过 inc 操作.
I have tried moving things into rax with mov and I have also tried the inc operation.
这是 asciiToDec 函数，注释得很好，我将 ASCII 数字的位置，然后将它们的数量压入堆栈，然后调用此函数.
Here is the asciiToDec function, well commented, I push the location of the ASCII numbers then the amount of them onto the stack then call this function.
asciiToDec: ; Converts a number in ASCII to decimal that the computer can understand
pop rax ; Remove the ret pointer so that it isnt popped off later when the other values are popped
pop qword[amount] ; Remove the amount of characters from the stack
pop qword[location] ; Remove the location from the stack
push rax ; Push the ret pointer back onto the stack
mov rax,1 ; Move 1 into rax since 0*x==0 so 1*x==10 where x=10
mov rbx,10 ; Move 10 into rbx
mov rcx,[amount] ; Move the amount of stuff into rcx
sub rcx,1 ; Subtract one since the one's digit needs to be multiplied by 1 not 10
;-----------------------------------;
loop1: ; Stage 1: Counts the power of 10 that is needed for the first number, highest digit
mul rbx ; Multiply rax by rbx, rax*10
sub rcx,1 ; Subtract 1 from rcx
cmp rcx,0 ; Test if rcx==0
jne loop1 ; Repeat if rcx>0
mov [power10],rax ; Move the power of ten into the power10 variable
xor rax,rax ; Set rax to 0 via xoring the bits to 0
mov rbx,[location] ; Move the location of the ASCII into rbx
;-----------------------------------;
loop2: ; Stage 2: Actually converts the ASCII to decimal by subtracting ASCII '0'
xor rcx,rcx ; Remove previous data
mov cl,byte[rbx+rax] ; Copy new data into the low byte of rcx
cmp cl,10 ; Next 4 lines: test for newlines and carrige returns, shouldn't have any but just making sure
je loop2 ; /\
cmp cl,13 ; /\
je loop2 ; /\
add rax,1 ; INC rax so we have the next byte
sub cl,'0' ; Make it decimal and not ASCII
cmp cl,9 ; Test if the value in cl is equal to 9
jg failFun ; If greater than 9 then the ASCII value in this index was not 0-9
push rax ; Get the data in rax out of the way so we can do some calculations with rax
mov al,cl ; Move the byte in cl to al, 0-9
mul qword[power10] ; Multiply rax (al is the lowest 8 bits of rax) by the power of 10
mov rcx,rax ; Move the val in rax back to rcx for later use
mov rax,[power10] ; Move the power of 10 to rax
push rbx ; Get the data in rbx out of the way, like rax
mov rbx,10 ; Move 10 into rbx
div rbx ; Divide rax (power of ten) by rbx (10) to get the next lower digit's power
pop rbx ; Get back the data that was in rbx
mov [power10],rax ; Move the power of 10 back into the `power10` variable from rax
pop rax ; Get rax's data back
add [total],rcx ; Add rcx to the total
cmp rax,[amount] ; Compare rax to the amount of characters
jne loop2 ; If we haven't gone through all the characters, loop again
pop rax ; Get the ret pointer out of the stack so I can have it on the top later
push qword[total] ; Move the total into the stack
push rax ; and push the ret pointer back on top
jmp clean ; Jump to clean
;-----------------------------------;
failFun: ; Stage 3: An option for the function to go through if stage 2 fails
push qword fail
push qword failLen
call print
pop rax
push qword 0
push rax
jmp clean
我希望它将 dec 数压入堆栈以便稍后弹出，但即使在添加操作和 mov 之后， 导致无限循环，因为 rax 也永远不会高于 0rax,[power10]rax 永远不会达到 [amount]GDB 输出:
I expect it to push the dec number onto the stack for popping later but instead, rax is never above 0 even after the add operation and the mov rax,[power10] which results in an infinite loop because rax never reaches [amount]
GDB output:
Starting program: /path/to/executable/a.out
1234
Breakpoint 1, loop2 () at common.asm:114
114 xor rcx,rcx ; Remove previous data
(gdb) info reg rax
rax 0x0 0
(gdb) nexti
115 mov cl,byte[rbx+rax] ; Copy new data into the low byte of rcx
(gdb)
116 cmp cl,10 ; Next 4 lines: test for newlines and carrige returns, shouldn't have any but just making sure
(gdb)
120 add rax,1 ; INC rax so we have the next byte
(gdb)
121 sub cl,'0' ; Make it decimal and not ASCII
(gdb) info reg rax
rax 0x0 0
推荐答案
NASM 被您的
/\注释混淆并忽略这些行.删除这些注释.*实际上反斜杠是行的延续，因此 nasm 认为以下几行是您评论的其余部分 - Jester
NASM is confused by your
/\comments and ignores the lines.Remove those comments. *Actually backslash is line continuation so nasm thinks the following lines are the rest of your comment - Jester
使用 \ 删除注释可以解决问题，因为 NASM 认为下一行是注释.VIM NASM 语法高亮不遵循此规则.
Removing the comment with a \ fixes the issue since NASM thinks the next lines are comments. VIM NASM syntax highlighting does not follow this rule.
来自 NASM 手册，3.1 NASM 源代码行的布局:
From the NASM manual, 3.1 Layout of a NASM Source Line:
NASM 使用反斜杠 (\) 作为行继续符；如果一行以反斜杠结尾，下一行被认为是反斜杠结尾行的一部分.
NASM uses backslash (
\) as the line continuation character; if a line ends with backslash, the next line is considered to be a part of the backslash-ended line.
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