blocks|key|1766556|text|阅读这篇讨论C/C%2B%2B内联汇编的文章是一个很好的开始：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1766557|http://www.codeproject.com/KB/cpp/edujini_inline_asm.aspx|offset|length|1766558|文章中的示例：|1766559|#include+<stdio.h>


int+main()+{
++++/*+Add+10+and+20+and+store+result+into+register+%25eax+*/
++++__asm__+(+"movl+$10,+%25eax;"
++++++++++++++++"movl+$20,+%25ebx;"
++++++++++++++++"addl+%25ebx,+%25eax;"
++++);

++++/*+Subtract+20+from+10+and+store+result+into+register+%25eax+*/
++++__asm__+(+"movl+$10,+%25eax;"
++++++++++++++++++++"movl+$20,+%25ebx;"
++++++++++++++++++++"subl+%25ebx,+%25eax;"
++++);

++++/*+Multiply+10+and+20+and+store+result+into+register+%25eax+*/
++++__asm__+(+"movl+$10,+%25eax;"
++++++++++++++++++++"movl+$20,+%25ebx;"
++++++++++++++++++++"imull+%25ebx,+%25eax;"
++++);

++++return+0+;
}|code-block|syntax|javascript|1766560|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1L|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@$D|V|E|W|1|X]]|A|$]]|$1|F|3|G|5|6|7|Y|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|Z|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|C]]]]

A good start would be reading this article which talk about inline assembly in C/C++:

<a href="http://www.codeproject.com/KB/cpp/edujini_inline_asm.aspx" rel="noreferrer">http://www.codeproject.com/KB/cpp/edujini_inline_asm.aspx</a>

Example from the article:

<pre><code>#include &lt;stdio.h&gt;


int main() {
 /* Add 10 and 20 and store result into register %eax */
 __asm__ ( "movl $10, %eax;"
 "movl $20, %ebx;"
 "addl %ebx, %eax;"
 );

 /* Subtract 20 from 10 and store result into register %eax */
 __asm__ ( "movl $10, %eax;"
 "movl $20, %ebx;"
 "subl %ebx, %eax;"
 );

 /* Multiply 10 and 20 and store result into register %eax */
 __asm__ ( "movl $10, %eax;"
 "movl $20, %ebx;"
 "imull %ebx, %eax;"
 );

 return 0 ;
}
</code></pre>

blocks|key|1551543|text|使用GCC|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1551544|__asm__("movl+%25edx,+%25eax\n\t"
++++++++"addl+$2,+%25eax\n\t");|code-block|syntax|javascript|1551545|使用VC%2B%2B|1551546|__asm+{
++mov+eax,+edx
++add+eax,+2
}|1551547|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html|1|http://msdn.microsoft.com/en-us/library/4ks26t93(VS.71).aspx^0|2|3|0|0|0|2|4|1|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|K|3|L|5|F|7|15|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

Using <a href="http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html" rel="noreferrer">GCC</a>

<pre><code>__asm__("movl %edx, %eax\n\t"
 "addl $2, %eax\n\t");
</code></pre>

Using <a href="http://msdn.microsoft.com/en-us/library/4ks26t93(VS.71).aspx" rel="noreferrer">VC++</a>

<pre><code>__asm {
 mov eax, edx
 add eax, 2
}
</code></pre>

blocks|key|1766618|text|在GCC身上，还有更多的事情要做。在指令中，你必须告诉编译器发生了什么变化，这样它的优化器就不会搞砸了。我不是专家，但有时它看起来像这样：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1766619|++++asm+("lock;+xaddl+%250,%252"+:+"=r"+(result)+:+"0"+(1),+"m"+(*atom)+:+"memory");|code-block|syntax|javascript|1766620|用C语言编写一些示例代码，然后让GCC生成汇编清单，然后修改代码，这是一个好主意。|1766621|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In GCC, there's more to it than that. In the instruction, you have to tell the compiler what changed, so that its optimizer doesn't screw up. I'm no expert, but sometimes it looks something like this:

<pre><code> asm ("lock; xaddl %0,%2" : "=r" (result) : "0" (1), "m" (*atom) : "memory");
</code></pre>

It's a good idea to write some sample code in C, then ask GCC to produce an assembly listing, then modify that code.

blocks|key|1551629|text|使用asm或__asm__函数(在编译器中有区别)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1551630|你也可以用fortran函数写fortran代码|1551631|asm("syscall");
fortran("Print+*,"J");|code-block|syntax|javascript|1551632|entityMap^0|2|3|6|7|0|5|7|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

use of <code>asm</code> or <code>__asm__</code> function ( in compilers have difference )
also you can write fortran codes with <code>fortran</code> function
<pre><code>asm(&quot;syscall&quot;);
fortran(&quot;Print *,&quot;J&quot;);
</code></pre>

I remember back in the day with the old borland DOS compiler you could do something like this:

<pre><code>asm {
 mov ax,ex
 etc etc...
}
</code></pre>

Is there a semi-platform independent way to do this now? I have a need to make a BIOS call, so if there was a way to do this without asm code, that would be equally useful to me.

Is there a way to insert assembly code into C?

编译器

我记得当时使用旧的borland DOS编译器，你可以做这样的事情：asm { mov ax,ex etc etc...}现在有没有一种半平台独立的方式来做到这一点？我需要进行BIOS调用，所以如果有一种方法可以在不使用asm代码的情况下实现这一点，那么它对我也同样有用。

问有没有办法将汇编代码插入到C中？
EN

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