| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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 1.3 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. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Using the GNU Compiler Collection (GCC): Size of an asm</title> |
| |
| <meta name="description" content="Using the GNU Compiler Collection (GCC): Size of an asm"> |
| <meta name="keywords" content="Using the GNU Compiler Collection (GCC): Size of an asm"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" rel="up" title="Using Assembly Language with C"> |
| <link href="Alternate-Keywords.html#Alternate-Keywords" rel="next" title="Alternate Keywords"> |
| <link href="Local-Reg-Vars.html#Local-Reg-Vars" rel="prev" title="Local Reg Vars"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Size-of-an-asm"></a> |
| <div class="header"> |
| <p> |
| Previous: <a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars" accesskey="p" rel="prev">Explicit Reg Vars</a>, Up: <a href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" accesskey="u" rel="up">Using Assembly Language with C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Size-of-an-asm-1"></a> |
| <h4 class="subsection">6.43.6 Size of an <code>asm</code></h4> |
| |
| <p>Some targets require that GCC track the size of each instruction used |
| in order to generate correct code. Because the final length of the |
| code produced by an <code>asm</code> statement is only known by the |
| assembler, GCC must make an estimate as to how big it will be. It |
| does this by counting the number of instructions in the pattern of the |
| <code>asm</code> and multiplying that by the length of the longest |
| instruction supported by that processor. (When working out the number |
| of instructions, it assumes that any occurrence of a newline or of |
| whatever statement separator character is supported by the assembler – |
| typically ‘<samp>;</samp>’ — indicates the end of an instruction.) |
| </p> |
| <p>Normally, GCC’s estimate is adequate to ensure that correct |
| code is generated, but it is possible to confuse the compiler if you use |
| pseudo instructions or assembler macros that expand into multiple real |
| instructions, or if you use assembler directives that expand to more |
| space in the object file than is needed for a single instruction. |
| If this happens then the assembler may produce a diagnostic saying that |
| a label is unreachable. |
| </p> |
| |
| |
| |
| </body> |
| </html> |
