⭐ 欢迎来到虫虫下载站！ | 📦 资源下载 📁 资源专辑 ℹ️ 关于我们
⭐ 虫虫下载站
📤 上传资源

📄 alpha-directives.html

📁 gcc手册
💻 HTML
字号:
🔍 
<html lang="en">

<head>

<title>Using as</title>

<meta http-equiv="Content-Type" content="text/html">

<meta name="description" content="Using as">

<meta name="generator" content="makeinfo 4.3">

<link href="http://www.gnu.org/software/texinfo/" rel="generator-home">

</head>

<body>

<div class="node">

<p>

Node:<a name="Alpha%20Directives">Alpha Directives</a>,

Next:<a rel="next" accesskey="n" href="Alpha-Opcodes.html#Alpha%20Opcodes">Alpha Opcodes</a>,

Previous:<a rel="previous" accesskey="p" href="Alpha-Floating-Point.html#Alpha%20Floating%20Point">Alpha Floating Point</a>,

Up:<a rel="up" accesskey="u" href="Alpha-Dependent.html#Alpha-Dependent">Alpha-Dependent</a>

<hr><br>

</div>



<h4 class="section">Alpha Assembler Directives</h4>



   <p><code>as</code> for the Alpha supports many additional directives for

compatibility with the native assembler.  This section describes them only

briefly.



   <p>These are the additional directives in <code>as</code> for the Alpha:



     <dl>

<dt><code>.arch </code><var>cpu</var><code></code>

     <dd>Specifies the target processor.  This is equivalent to the

<code>-m</code><var>cpu</var><code></code> command-line option.  See <a href="Alpha-Options.html#Alpha%20Options">Options</a>,

for a list of values for <var>cpu</var>.



     <br><dt><code>.ent </code><var>function</var><code>[, </code><var>n</var><code>]</code>

     <dd>Mark the beginning of <var>function</var>.  An optional number may follow for

compatibility with the OSF/1 assembler, but is ignored.  When generating

<code>.mdebug</code> information, this will create a procedure descriptor for

the function.  In ELF, it will mark the symbol as a function a-la the

generic <code>.type</code> directive.



     <br><dt><code>.end </code><var>function</var><code></code>

     <dd>Mark the end of <var>function</var>.  In ELF, it will set the size of the symbol

a-la the generic <code>.size</code> directive.



     <br><dt><code>.mask </code><var>mask</var><code>, </code><var>offset</var><code></code>

     <dd>Indicate which of the integer registers are saved in the current

function's stack frame.  <var>mask</var> is interpreted a bit mask in which

bit <var>n</var> set indicates that register <var>n</var> is saved.  The registers

are saved in a block located <var>offset</var> bytes from the <dfn>canonical

frame address</dfn> (CFA) which is the value of the stack pointer on entry to

the function.  The registers are saved sequentially, except that the

return address register (normally <code>$26</code>) is saved first.



     <p>This and the other directives that describe the stack frame are

currently only used when generating <code>.mdebug</code> information.  They

may in the future be used to generate DWARF2 <code>.debug_frame</code> unwind

information for hand written assembly.



     <br><dt><code>.fmask </code><var>mask</var><code>, </code><var>offset</var><code></code>

     <dd>Indicate which of the floating-point registers are saved in the current

stack frame.  The <var>mask</var> and <var>offset</var> parameters are interpreted

as with <code>.mask</code>.



     <br><dt><code>.frame </code><var>framereg</var><code>, </code><var>frameoffset</var><code>, </code><var>retreg</var><code>[, </code><var>argoffset</var><code>]</code>

     <dd>Describes the shape of the stack frame.  The frame pointer in use is

<var>framereg</var>; normally this is either <code>$fp</code> or <code>$sp</code>.  The

frame pointer is <var>frameoffset</var> bytes below the CFA.  The return

address is initially located in <var>retreg</var> until it is saved as

indicated in <code>.mask</code>.  For compatibility with OSF/1 an optional

<var>argoffset</var> parameter is accepted and ignored.  It is believed to

indicate the offset from the CFA to the saved argument registers.



     <br><dt><code>.prologue </code><var>n</var><code></code>

     <dd>Indicate that the stack frame is set up and all registers have been

spilled.  The argument <var>n</var> indicates whether and how the function

uses the incoming <dfn>procedure vector</dfn> (the address of the called

function) in <code>$27</code>.  0 indicates that <code>$27</code> is not used; 1

indicates that the first two instructions of the function use <code>$27</code>

to perform a load of the GP register; 2 indicates that <code>$27</code> is

used in some non-standard way and so the linker cannot elide the load of

the procedure vector during relaxation.



     <br><dt><code>.gprel32 </code><var>expression</var><code></code>

     <dd>Computes the difference between the address in <var>expression</var> and the

GP for the current object file, and stores it in 4 bytes.  In addition

to being smaller than a full 8 byte address, this also does not require

a dynamic relocation when used in a shared library.



     <br><dt><code>.t_floating </code><var>expression</var><code></code>

     <dd>Stores <var>expression</var> as an <small>IEEE</small> double precision value.



     <br><dt><code>.s_floating </code><var>expression</var><code></code>

     <dd>Stores <var>expression</var> as an <small>IEEE</small> single precision value.



     <br><dt><code>.f_floating </code><var>expression</var><code></code>

     <dd>Stores <var>expression</var> as a VAX F format value.



     <br><dt><code>.g_floating </code><var>expression</var><code></code>

     <dd>Stores <var>expression</var> as a VAX G format value.



     <br><dt><code>.d_floating </code><var>expression</var><code></code>

     <dd>Stores <var>expression</var> as a VAX D format value.



     <br><dt><code>.set </code><var>feature</var><code></code>

     <dd>Enables or disables various assembler features.  Using the positive

name of the feature enables while using <code>no</code><var>feature</var><code></code> disables.



          <dl>

<dt><code>at</code>

          <dd>Indicates that macro expansions may clobber the <dfn>assembler

temporary</dfn> (<code>$at</code> or <code>$28</code>) register.  Some macros may not be

expanded without this and will generate an error message if <code>noat</code>

is in effect.  When <code>at</code> is in effect, a warning will be generated

if <code>$at</code> is used by the programmer.



          <br><dt><code>macro</code>

          <dd>Enables the expasion of macro instructions.  Note that variants of real

instructions, such as <code>br label</code> vs <code>br $31,label</code> are

considered alternate forms and not macros.



          <br><dt><code>move</code>

          <dd><dt><code>reorder</code>

          <dd><dt><code>volatile</code>

          <dd>These control whether and how the assembler may re-order instructions. 

Accepted for compatibility with the OSF/1 assembler, but <code>as</code>

does not do instruction scheduling, so these features are ignored. 

</dl>

</dl>



   <p>The following directives are recognized for compatibility with the OSF/1

assembler but are ignored.



<pre class="example">     .proc           .aproc

     .reguse         .livereg

     .option         .aent

     .ugen           .eflag

     .alias          .noalias

     </pre>



   </body></html>

⌨️ 快捷键说明

复制代码 Ctrl + C
搜索代码 Ctrl + F
全屏模式 F11
切换主题 Ctrl + Shift + D
显示快捷键 ?
增大字号 Ctrl + =
减小字号 Ctrl + -