汇编代码 Assembly(*.S): movl $0xffff, %eax //把0xffff给eax 内联汇编 Inline assembly(*.c): 字符串 GCC内联汇编-语法 asm("assmbler template" //assmbler template就是example 1 的那个字符串的内容(汇编语句) :output operands (optional) //可选
Whatever is inside the asm call will be placed as is in the assembly output generated by the C compiler. This assembly output is then fed to the assembler. This kind of inline assembly is good for doing things which can not be directly done using C, but we cant place these instructions ...
asm ("movl %%eax, %0\n" : "=r"(out_val)); 该指令的作用是将%eax的值返回给%0所引用的C语言变量out_val,根据"=r"约束可知具体的操作流程为:先将%eax值复制给任一GPR,最终由该寄存器将值写入%0所代表的变量中。"r"约束指明gcc可以先将%eax值存入任一可用的寄存器,然后由该寄存器负责更新内存变量。
: "constraints" (in_var) 其中,constraints可以是gcc支持的各种约束方式,in_var通常为C语言提供的输入变量。 与output operands类似,当有多个input时,典型格式为: : "constraints1" (in_var1), "constraints2" (in_var2), "constraints3" (in_var3), ... 当然,input operands + output operands的总数通...
内联汇编称为inline assembly,GCC支持在C代码中直接嵌入汇编代码,称为GCC inline assembly。内联汇编的主要作用如下: 提高程序性能:例如可以使用内联汇编实现高效的循环、条件判断等操… someone 汇编语言入门四:打通C和汇编语言 不吃油条 嵌入式汇编(内联汇编) Linux码农 8. 从0学ARM-内联汇编、混合汇编、ATPCS规则 ...
Inline assembly - start from scratchXiaofeng GuanChaojie Xiao
阅读Linux内核源码或对代码做性能优化时,经常会有在C语言中嵌入一段汇编代码的需求,这种嵌入汇编在CS术语上叫做inline assembly。本文的笔记试图说明Inline Assembly的基本语法规则和用法(建议英文阅读能力较强的同学直接阅读本文参考资料中推荐的技术文章 ^_^)。
Even though it's not technically part of the C99 standard, inline assembly support is crucial to the effective use of this compiler. Accordingly, all relevant features of inline assembly should work according to the GCC documentation. It's unclear exactly what this entails, so this issue is a...
For example, using “f” means that the corresponding operand will be placed by the compiler into a register prior to the instruction being fetched, and its value is specified in the inline assembly using a C/C++ expression. ▪ expression is the C/C++ expression, variable, or pointer ...
in("eax") info, lateout("eax") a, out("edi") b, out("ecx") c, out("edx") d, ) 与GCC 内联汇编语法一样,Rust 希望即使需要手写汇编,程序员也能将一部分工作交给编译器来高效完成,这部分工作就是寄存器分配,毕竟只有编译器了解内联汇编前后的上下文,知道该怎么分配寄存器最合适。