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diff --git a/share/doc/stabs/Local-Variable-Parameters.html b/share/doc/stabs/Local-Variable-Parameters.html new file mode 100644 index 0000000..7e26292 --- /dev/null +++ b/share/doc/stabs/Local-Variable-Parameters.html @@ -0,0 +1,143 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1992-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>STABS: Local Variable Parameters</title> + +<meta name="description" content="STABS: Local Variable Parameters"> +<meta name="keywords" content="STABS: Local Variable Parameters"> +<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="previous" title="Register Parameters"> +<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="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="previous">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="previous">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> |