You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
143 lines
7.0 KiB
HTML
143 lines
7.0 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1992-2019 Free Software Foundation, Inc.
|
||
|
|
Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
|
||
|
|
and David MacKenzie.
|
||
|
|
|
||
|
|
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 no
|
||
|
|
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
|
||
|
|
Texts. A copy of the license is included in the section entitled "GNU
|
||
|
|
Free Documentation License". -->
|
||
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Local Variable Parameters (STABS)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Local Variable Parameters (STABS)">
|
||
|
|
<meta name="keywords" content="Local Variable Parameters (STABS)">
|
||
|
|
<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="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Parameters.html#Parameters" rel="up" title="Parameters">
|
||
|
|
<link href="Reference-Parameters.html#Reference-Parameters" rel="next" title="Reference Parameters">
|
||
|
|
<link href="Register-Parameters.html#Register-Parameters" rel="prev" title="Register Parameters">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
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.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="Local-Variable-Parameters"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Reference-Parameters.html#Reference-Parameters" accesskey="n" rel="next">Reference Parameters</a>, Previous: <a href="Register-Parameters.html#Register-Parameters" accesskey="p" rel="prev">Register Parameters</a>, Up: <a href="Parameters.html#Parameters" accesskey="u" rel="up">Parameters</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<a name="Storing-Parameters-as-Local-Variables"></a>
|
||
|
|
<h4 class="subsection">4.7.2 Storing Parameters as Local Variables</h4>
|
||
|
|
|
||
|
|
<p>There is a case similar to an argument in a register, which is an
|
||
|
|
argument that is actually stored as a local variable. Sometimes this
|
||
|
|
happens when the argument was passed in a register and then the compiler
|
||
|
|
stores it as a local variable. If possible, the compiler should claim
|
||
|
|
that it’s in a register, but this isn’t always done.
|
||
|
|
</p>
|
||
|
|
<p>If a parameter is passed as one type and converted to a smaller type by
|
||
|
|
the prologue (for example, the parameter is declared as a <code>float</code>,
|
||
|
|
but the calling conventions specify that it is passed as a
|
||
|
|
<code>double</code>), then GCC2 (sometimes) uses a pair of symbols. The first
|
||
|
|
symbol uses symbol descriptor ‘<samp>p</samp>’ and the type which is passed.
|
||
|
|
The second symbol has the type and location which the parameter actually
|
||
|
|
has after the prologue. For example, suppose the following C code
|
||
|
|
appears with no prototypes involved:
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example">void
|
||
|
|
subr (f)
|
||
|
|
float f;
|
||
|
|
{
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>if <code>f</code> is passed as a double at stack offset 8, and the prologue
|
||
|
|
converts it to a float in register number 0, then the stabs look like:
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example">.stabs "f:p13",160,0,3,8 # <span class="roman">160 is <code>N_PSYM</code>, here 13 is <code>double</code></span>
|
||
|
|
.stabs "f:r12",64,0,3,0 # <span class="roman">64 is <code>N_RSYM</code>, here 12 is <code>float</code></span>
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>In both stabs 3 is the line number where <code>f</code> is declared
|
||
|
|
(see <a href="Line-Numbers.html#Line-Numbers">Line Numbers</a>).
|
||
|
|
</p>
|
||
|
|
<a name="index-N_005fLSYM_002c-for-parameter"></a>
|
||
|
|
<p>GCC, at least on the 960, has another solution to the same problem. It
|
||
|
|
uses a single ‘<samp>p</samp>’ symbol descriptor for an argument which is stored
|
||
|
|
as a local variable but uses <code>N_LSYM</code> instead of <code>N_PSYM</code>. In
|
||
|
|
this case, the value of the symbol is an offset relative to the local
|
||
|
|
variables for that function, not relative to the arguments; on some
|
||
|
|
machines those are the same thing, but not on all.
|
||
|
|
</p>
|
||
|
|
<p>On the VAX or on other machines in which the calling convention includes
|
||
|
|
the number of words of arguments actually passed, the debugger (GDB at
|
||
|
|
least) uses the parameter symbols to keep track of whether it needs to
|
||
|
|
print nameless arguments in addition to the formal parameters which it
|
||
|
|
has printed because each one has a stab. For example, in
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example">extern int fprintf (FILE *stream, char *format, …);
|
||
|
|
…
|
||
|
|
fprintf (stdout, "%d\n", x);
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>there are stabs for <code>stream</code> and <code>format</code>. On most machines,
|
||
|
|
the debugger can only print those two arguments (because it has no way
|
||
|
|
of knowing that additional arguments were passed), but on the VAX or
|
||
|
|
other machines with a calling convention which indicates the number of
|
||
|
|
words of arguments, the debugger can print all three arguments. To do
|
||
|
|
so, the parameter symbol (symbol descriptor ‘<samp>p</samp>’) (not necessarily
|
||
|
|
‘<samp>r</samp>’ or symbol descriptor omitted symbols) needs to contain the
|
||
|
|
actual type as passed (for example, <code>double</code> not <code>float</code> if it
|
||
|
|
is passed as a double and converted to a float).
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Reference-Parameters.html#Reference-Parameters" accesskey="n" rel="next">Reference Parameters</a>, Previous: <a href="Register-Parameters.html#Register-Parameters" accesskey="p" rel="prev">Register Parameters</a>, Up: <a href="Parameters.html#Parameters" accesskey="u" rel="up">Parameters</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|