Say hello to x86_64 Assembly [part 5]
最近在学习x64汇编,在github上面找到了一点学习资料,入门级别的,因为想细致的学习一下,所以顺便久把作者的内容都翻译了一下,也不知道自己翻译的是否合适,请大家看看有问题的地方请批评指正.第一次做翻译,做的不好请大家原谅,
作者原文
这是Say hello to x86_64 Assembly的第五部分，下面我们将介绍宏。它不会是关于x86_64的博客文章，主要是关于nasm汇编程序及其预处理器的。如果你对它感兴趣，请看下一篇。
It is a fifth part of Say hello to x86_64 Assembly and here we will look at macros. It will not be blog post about x86_64, mainly it will be about nasm assembler and it’s preprocessor. If you’re interesting in it read next.
宏
Macros
NASM支持两种形式的宏：
-单行
-多行
所有单行宏都必须从%define指令开始。其形式如下：
NASM supports two form of macro:
All single-line macro must start from %define directive. It form is following:
%define macro_name(parameter) value
Nasm宏的行为和外观与C中的非常相似。例如，我们可以创建以下单行宏：
Nasm macro behaves and looks very similar as in C. For example, we can create following single-line macro:
%define argc rsp + 8
%define cliArg1 rsp + 24
在代码中使用它：
and than use it in code:
;;
;; argc will be expanded to rsp + 8
;;
mov rax, [argc]
cmp rax, 3
jne .mustBe3args
多行宏以%macro nasm指令开头，以%endmacro结尾。一般形式如下：
Multiline macro starts with %macro nasm directive and end with %endmacro. It general form is following:
%macro number_of_parameters
instruction
instruction
instruction
%endmacro
例如：
For example:
%macro bootstrap 1
push ebp
mov ebp,esp
%endmacro
我们可以使用它：
And we can use it:
_start:
bootstrap
例如，让我们看看PRINT宏：
For example let’s look at PRINT macro:
%macro PRINT 1
pusha
pushf
jmp %%astr
%%str db %1, 0
%%strln equ $-%%str
%%astr: _syscall_write %%str, %%strln
popf
popa
%endmacro
%macro _syscall_write 2
mov rax, 1
mov rdi, 1
mov rsi, %%str
mov rdx, %%strln
syscall
%endmacro
让我们试着浏览一下它的宏并了解它是如何工作的：在第一行，我们用一个参数定义了PRINT宏。然后推送所有通用寄存器（使用pusha指令）和标记寄存器（使用pushf指令）。在此之后，我们将跳转到%%astr label。请注意，宏中定义的所有标签必须以“%”开头。现在我们转到带2个参数的 __syscall_write宏。让我们看看系统调用写入实现。您可以记住，我们在以前的所有文章中都使用写入系统调用将字符串打印到stdout。看起来是这样的：
Let’s try to go through it macro and understand how it works: At first line we defined PRINT macro with one parameter. Than we push all general registers (with pusha instruction) and flag register with (with pushf instruction). After this we jump to %%astr label. Pay attention that all labels which defined in macro must start with %%. Now we move to syscall_write macro with 2 parameter. Let’s look on syscall_write implementation. You can remember that we use write system call in all previous posts for printing string to stdout. It looks like this:
;; write syscall number
mov rax, 1
;; file descriptor, standard output
mov rdi, 1
;; message address
mov rsi, msg
;; length of message
mov rdx, 14
;; call write syscall
syscall
在__syscall_write宏中，我们定义了前两条指令，用于将1放入rax（写系统调用号）和rdi（stdout文件描述符）。然后我们将%str放入rsi寄存器（指向字符串的指针），其中，%str是本地标签，它是PRINT宏的第一个参数（注意宏参数通过$parameter_number访问），以0结尾（每个字符串必须以0结尾）。以及计算字符串长度的%strlen。在此之后，我们使用syscall指令调用系统调用，仅此而已。
In our __syscall_write macro we define first two instruction for putting 1 to rax (write system call number) and rdi (stdout file descriptor). Than we put %%str to rsi register (pointer to string), where %%str is local label to which is get first parameter of PRINT macro (pay attention that macro parameter access by $parameter_number) and end with 0 (every string must end with zero). And %%strlen which calculates string length. After this we call system call with syscall instruction and that’s all.
Now we can use it:
label: PRINT "Hello World!"
有用的标准宏
Useful standard macros
NASM支持以下标准宏：
NASM supports following standard macros:
结构
struc
我们可以使用'STRUC'和'ENDSTRUC'来定义数据结构。例如：
We can use STRUC and ENDSTRUC for data structure defintion. For example:
struc person
name: resb 10
age: resb 1
endstruc
现在我们可以举例说明我们的结构：
And now we can make instance of our structure:
section .data
p: istruc person
at name db "name"
at age db 25
iend
section .text
_start:
mov rax, [p + person.name]
%include
我们可以包含其他程序集文件并跳转到其中的标签或使用%include指令调用函数。
We can include other assembly files and jump to there labels or call functions with %include directive.
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