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.
133 lines
7.3 KiB
HTML
133 lines
7.3 KiB
HTML
<!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>ELF Linker Relocation (STABS)</title>
|
|
|
|
<meta name="description" content="ELF Linker Relocation (STABS)">
|
|
<meta name="keywords" content="ELF Linker Relocation (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="Stab-Sections.html#Stab-Sections" rel="up" title="Stab Sections">
|
|
<link href="GNU-Free-Documentation-License.html#GNU-Free-Documentation-License" rel="next" title="GNU Free Documentation License">
|
|
<link href="Stab-Section-Basics.html#Stab-Section-Basics" rel="prev" title="Stab Section Basics">
|
|
<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="ELF-Linker-Relocation"></a>
|
|
<div class="header">
|
|
<p>
|
|
Previous: <a href="Stab-Section-Basics.html#Stab-Section-Basics" accesskey="p" rel="prev">Stab Section Basics</a>, Up: <a href="Stab-Sections.html#Stab-Sections" accesskey="u" rel="up">Stab Sections</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="Having-the-Linker-Relocate-Stabs-in-ELF"></a>
|
|
<h3 class="appendixsec">F.2 Having the Linker Relocate Stabs in ELF</h3>
|
|
|
|
<p>This section describes some Sun hacks for Stabs in ELF; it does not
|
|
apply to COFF or SOM. While <small>GDB</small> no longer supports this hack
|
|
for Sun Stabs in ELF, this section is kept to document the issue.
|
|
</p>
|
|
<p>To keep linking fast, you don’t want the linker to have to relocate very
|
|
many stabs. Making sure this is done for <code>N_SLINE</code>,
|
|
<code>N_RBRAC</code>, and <code>N_LBRAC</code> stabs is the most important thing
|
|
(see the descriptions of those stabs for more information). But Sun’s
|
|
stabs in ELF has taken this further, to make all addresses in the
|
|
<code>n_value</code> field (functions and static variables) relative to the
|
|
source file. For the <code>N_SO</code> symbol itself, Sun simply omits the
|
|
address. To find the address of each section corresponding to a given
|
|
source file, the compiler puts out symbols giving the address of each
|
|
section for a given source file. Since these are ELF (not stab)
|
|
symbols, the linker relocates them correctly without having to touch the
|
|
stabs section. They are named <code>Bbss.bss</code> for the bss section,
|
|
<code>Ddata.data</code> for the data section, and <code>Drodata.rodata</code> for
|
|
the rodata section. For the text section, there is no such symbol (but
|
|
there should be, see below). For an example of how these symbols work,
|
|
See <a href="Stab-Section-Transformations.html#Stab-Section-Transformations">Stab Section Transformations</a>. GCC does not provide these symbols;
|
|
it instead relies on the stabs getting relocated. Thus addresses which
|
|
would normally be relative to <code>Bbss.bss</code>, etc., are already
|
|
relocated. The Sun linker provided with Solaris 2.2 and earlier
|
|
relocates stabs using normal ELF relocation information, as it would do
|
|
for any section. Sun has been threatening to kludge their linker to not
|
|
do this (to speed up linking), even though the correct way to avoid
|
|
having the linker do these relocations is to have the compiler no longer
|
|
output relocatable values. Last I heard they had been talked out of the
|
|
linker kludge. See Sun point patch 101052-01 and Sun bug 1142109. With
|
|
the Sun compiler this affects ‘<samp>S</samp>’ symbol descriptor stabs
|
|
(see <a href="Statics.html#Statics">Statics</a>) and functions (see <a href="Procedures.html#Procedures">Procedures</a>). In the latter
|
|
case, to adopt the clean solution (making the value of the stab relative
|
|
to the start of the compilation unit), it would be necessary to invent a
|
|
<code>Ttext.text</code> symbol, analogous to the <code>Bbss.bss</code>, etc.,
|
|
symbols. I recommend this rather than using a zero value and getting
|
|
the address from the ELF symbols.
|
|
</p>
|
|
<p>Finding the correct <code>Bbss.bss</code>, etc., symbol is difficult, because
|
|
the linker simply concatenates the <code>.stab</code> sections from each
|
|
<samp>.o</samp> file without including any information about which part of a
|
|
<code>.stab</code> section comes from which <samp>.o</samp> file. The way GDB use to
|
|
do this is to look for an ELF <code>STT_FILE</code> symbol which has the same
|
|
name as the last component of the file name from the <code>N_SO</code> symbol
|
|
in the stabs (for example, if the file name is <samp>../../gdb/main.c</samp>,
|
|
it looks for an ELF <code>STT_FILE</code> symbol named <code>main.c</code>). This
|
|
loses if different files have the same name (they could be in different
|
|
directories, a library could have been copied from one system to
|
|
another, etc.). It would be much cleaner to have the <code>Bbss.bss</code>
|
|
symbols in the stabs themselves. Having the linker relocate them there
|
|
is no more work than having the linker relocate ELF symbols, and it
|
|
solves the problem of having to associate the ELF and stab symbols.
|
|
However, no one has yet designed or implemented such a scheme.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Previous: <a href="Stab-Section-Basics.html#Stab-Section-Basics" accesskey="p" rel="prev">Stab Section Basics</a>, Up: <a href="Stab-Sections.html#Stab-Sections" accesskey="u" rel="up">Stab Sections</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>
|