| <html lang="en"> |
| <head> |
| <title>Asm Labels - Using the GNU Compiler Collection (GCC)</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Using the GNU Compiler Collection (GCC)"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions"> |
| <link rel="prev" href="Constraints.html#Constraints" title="Constraints"> |
| <link rel="next" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars" title="Explicit Reg Vars"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, |
| 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, |
| 2008 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.2 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Funding Free Software'', the Front-Cover |
| Texts being (a) (see below), and with the Back-Cover Texts being (b) |
| (see below). A copy of the license is included in the section entitled |
| ``GNU Free Documentation License''. |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development.--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Asm-Labels"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>, |
| Previous: <a rel="previous" accesskey="p" href="Constraints.html#Constraints">Constraints</a>, |
| Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">6.41 Controlling Names Used in Assembler Code</h3> |
| |
| <p><a name="index-assembler-names-for-identifiers-2583"></a><a name="index-names-used-in-assembler-code-2584"></a><a name="index-identifiers_002c-names-in-assembler-code-2585"></a> |
| You can specify the name to be used in the assembler code for a C |
| function or variable by writing the <code>asm</code> (or <code>__asm__</code>) |
| keyword after the declarator as follows: |
| |
| <pre class="smallexample"> int foo asm ("myfoo") = 2; |
| </pre> |
| <p class="noindent">This specifies that the name to be used for the variable <code>foo</code> in |
| the assembler code should be ‘<samp><span class="samp">myfoo</span></samp>’ rather than the usual |
| ‘<samp><span class="samp">_foo</span></samp>’. |
| |
| <p>On systems where an underscore is normally prepended to the name of a C |
| function or variable, this feature allows you to define names for the |
| linker that do not start with an underscore. |
| |
| <p>It does not make sense to use this feature with a non-static local |
| variable since such variables do not have assembler names. If you are |
| trying to put the variable in a particular register, see <a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>. GCC presently accepts such code with a warning, but will |
| probably be changed to issue an error, rather than a warning, in the |
| future. |
| |
| <p>You cannot use <code>asm</code> in this way in a function <em>definition</em>; but |
| you can get the same effect by writing a declaration for the function |
| before its definition and putting <code>asm</code> there, like this: |
| |
| <pre class="smallexample"> extern func () asm ("FUNC"); |
| |
| func (x, y) |
| int x, y; |
| /* <span class="roman">...</span> */ |
| </pre> |
| <p>It is up to you to make sure that the assembler names you choose do not |
| conflict with any other assembler symbols. Also, you must not use a |
| register name; that would produce completely invalid assembler code. GCC |
| does not as yet have the ability to store static variables in registers. |
| Perhaps that will be added. |
| |
| </body></html> |
| |
