251 lines
6.0 KiB
Markdown
251 lines
6.0 KiB
Markdown
# 08 - C 语言操作
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Viper 通过 `c` 模块提供对 C 语言底层特性的访问，包括指针操作、内联汇编、预处理指令等。
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## 指针操作
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### 取地址 `c.Addr`
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```python
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x: t.CInt = 42
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p: t.CInt | t.CPtr = c.Addr(x) # int* p = &x;
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```
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对结构体成员取地址：
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```python
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res: t.CInt = fat32.opendir("/", c.Addr(dp)) # res = fat32_opendir("/", &dp);
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```
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对数组取地址：
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```python
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viperlib.snprintf(c.Addr(buf), 64, "hello %d", 42) # snprintf(&buf, 64, "hello %d", 42);
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```
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### 解引用 `c.Deref`
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```python
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ptr: Sheet | t.CPtr = c.Addr(sheet_obj)
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obj: Sheet = c.Deref(ptr) # struct Sheet obj = *ptr;
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```
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### 内存拷贝 `c.Load`
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```python
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c.Load(ptr, value) # *ptr = *value;
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```
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### 解引用赋值 `c.DerefAs`
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```python
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c.DerefAs(ptr, value) # *ptr = value;
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```
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### 赋值 `c.Set`
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```python
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c.Set(target, value) # target = value;
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```
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## 内联汇编 `c.Asm`
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Viper 提供了声明式的内联汇编语法，编译为 GCC 风格的 `__asm__ __volatile__` 语句。
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### 基本用法
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```python
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c.Asm("nop") # __asm__ __volatile__("nop");
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```
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### 带操作数的汇编
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使用 f-string 和 `c.AsmInp` / `c.AsmOut` 标记操作数：
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```python
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saved_rdi: t.CUnsignedLong
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c.Asm(f"mov {c.AsmOut(saved_rdi, t.ASM_DESCR.OUTPUT_REG)}, rdi",
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op=[t.ASM_DESCR.CLOBBER_MEMORY, t.ASM_DESCR.CLOBBER_RDI])
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```
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等价 C 代码：
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```c
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__asm__ __volatile__(
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"mov %0, rdi"
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: "=r"(saved_rdi)
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:
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: "memory", "rdi"
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);
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```
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### 输入操作数 `c.AsmInp`
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```python
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msg: t.CConst | t.CChar | t.CPtr = "Hello"
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c.Asm(f"mov rdi, {c.AsmInp(msg, t.ASM_DESCR.REG_ANY)}",
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op=[t.ASM_DESCR.CLOBBER_MEMORY, t.ASM_DESCR.CLOBBER_RAX])
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```
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### 完整示例
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```python
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c.Asm(f"""mov rdi, {c.AsmInp(msg, t.ASM_DESCR.REG_ANY)}
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call {c.AsmInp(log_info_fn, t.ASM_DESCR.REG_ANY)}""",
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op=[t.ASM_DESCR.CLOBBER_MEMORY, t.ASM_DESCR.CLOBBER_RAX,
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t.ASM_DESCR.CLOBBER_RCX, t.ASM_DESCR.CLOBBER_RDX,
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t.ASM_DESCR.CLOBBER_RDI, t.ASM_DESCR.CLOBBER_RSI,
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t.ASM_DESCR.CLOBBER_R8, t.ASM_DESCR.CLOBBER_R9,
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t.ASM_DESCR.CLOBBER_R10, t.ASM_DESCR.CLOBBER_R11])
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```
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### ASM_DESCR 约束字符
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#### 操作数修饰符
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| 常量 | 值 | 说明 |
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|------|----|------|
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| `MODIFIER_OUTPUT` | `=` | 输出操作数 |
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| `MODIFIER_READWRITE` | `+` | 读写操作数 |
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| `MODIFIER_INPUT` | `` | 输入操作数（默认） |
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| `MODIFIER_GLOBAL` | `&` | 全局操作数 |
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#### 寄存器约束
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| 常量 | 值 | 说明 |
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|------|----|------|
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| `REG_ANY` | `r` | 任何通用寄存器 |
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| `REG_EAX` / `REG_RAX` | `a` | EAX/RAX |
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| `REG_EBX` / `REG_RBX` | `b` | EBX/RBX |
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| `REG_ECX` / `REG_RCX` | `c` | ECX/RCX |
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| `REG_EDX` / `REG_RDX` | `d` | EDX/RDX |
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| `REG_ESI` / `REG_RSI` | `S` | ESI/RSI |
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| `REG_EDI` / `REG_RDI` | `D` | EDI/RDI |
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| `REG_XMM` | `x` | XMM 寄存器 |
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#### 内存与立即数
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| 常量 | 值 | 说明 |
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|------|----|------|
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| `MEMORY` | `m` | 内存操作数 |
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| `IMMEDIATE` | `i` | 立即数 |
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| `ANY` | `g` | 通用寄存器/内存/立即数 |
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#### 预定义组合约束
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| 常量 | 值 | 说明 |
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|------|----|------|
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| `OUTPUT_REG` | `=r` | 输出，通用寄存器 |
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| `OUTPUT_MEM` | `=m` | 输出，内存 |
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| `OUTPUT_EAX` | `=a` | 输出，EAX/RAX |
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| `INPUT_REG` | `r` | 输入，通用寄存器 |
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| `INPUT_MEM` | `m` | 输入，内存 |
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| `INPUT_IMM` | `i` | 输入，立即数 |
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#### 破坏描述符
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| 常量 | 说明 |
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|------|------|
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| `CLOBBER_EAX` / `CLOBBER_RAX` | 破坏 EAX/RAX |
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| `CLOBBER_EBX` / `CLOBBER_RBX` | 破坏 EBX/RBX |
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| `CLOBBER_ECX` / `CLOBBER_RCX` | 破坏 ECX/RCX |
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| `CLOBBER_EDX` / `CLOBBER_RDX` | 破坏 EDX/RDX |
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| `CLOBBER_ESI` / `CLOBBER_RSI` | 破坏 ESI/RSI |
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| `CLOBBER_EDI` / `CLOBBER_RDI` | 破坏 EDI/RDI |
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| `CLOBBER_CC` | 破坏条件码（标志寄存器） |
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| `CLOBBER_MEMORY` | 破坏内存 |
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| `CLOBBER_R8` ~ `CLOBBER_R15` | 破坏 R8~R15 |
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## 预处理指令
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Viper 通过 `c` 模块的函数调用实现 C 预处理指令。
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### #define
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```python
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c.CDefine("MAX_SIZE", 1024) # #define MAX_SIZE 1024
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```
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上述方法容易引起未定义行为，至少是不便于理解，更常用的方式是使用类型注解：
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```python
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MAX_SIZE: t.CDefine = 1024 # #define MAX_SIZE 1024
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```
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### 条件编译
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```python
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c.CIfndef(HEADER_H) # #ifndef HEADER_H
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c.CDefine(HEADER_H) # #define HEADER_H
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c.CEndif() # #endif
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```
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```python
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c.CIfdef(DEBUG) # #ifdef DEBUG
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c.CEndif() # #endif
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```
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```python
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c.CIf(VERSION > 2) # #if VERSION > 2
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c.CElif(VERSION > 1) # #elif VERSION > 1
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c.CElse() # #else
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c.CEndif() # #endif
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```
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### #undef
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```python
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c.Undef(MACRO_NAME) # #undef MACRO_NAME
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```
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### #error
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```python
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c.CError("Platform not supported") # #error "Platform not supported"
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```
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### #pragma
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> 此关键字已不再支持
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```python
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c.CPragma("GCC diagnostic push") # #pragma GCC diagnostic push
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```
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### ## 连接符
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> 此方法可能已经不再支持
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```python
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c.TokenPast("PREFIX_", "NAME") # PREFIX_ ## NAME
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```
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由于编译器设计，以及不需要像 `C` 一样做大量字符替换，对于上述所有的条件宏都远比 `C` 差，实际工程中不推荐使用条件宏，后期将完善宏的设计，引入模板等。
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## 仅声明 `c.State`
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`c.State` 用于声明但不定义函数或变量：
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```python
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def isr0() -> t.CExtern | t.CVoid | c.State: pass # extern void isr0();
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```
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## LLVM IR 内联
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### c.LLVMIR
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直接嵌入 LLVM IR 指令来实现高效且跨平台的汇编操作：
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```python
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c.LLVMIR(f"add i32 {c.LInp(a)}, {c.LInp(b)}", t.CInt)
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```
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### c.LInp / c.LOut
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标记 LLVM IR 的输入/输出操作数：
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```python
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c.LInp(expr) # 输入操作数
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c.LOut(expr) # 输出操作数
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```
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## 运算符重载
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`@t.Object` 类支持运算符重载，详见 [06-oop.md 中 运算符重载](06-oop.md#运算符重载)。
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