107 lines
5.9 KiB
HTML
107 lines
5.9 KiB
HTML
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<html lang="en">
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<head>
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<title>Statics - STABS</title>
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<meta name="description" content="STABS">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Variables.html#Variables" title="Variables">
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<link rel="prev" href="Common-Blocks.html#Common-Blocks" title="Common Blocks">
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<link rel="next" href="Based-Variables.html#Based-Variables" title="Based Variables">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1992-2019 Free Software Foundation, Inc.
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Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
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and David MacKenzie.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled ``GNU
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Free Documentation License''.-->
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</head>
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<body>
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<div class="node">
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<a name="Statics"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Based-Variables.html#Based-Variables">Based Variables</a>,
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Previous: <a rel="previous" accesskey="p" href="Common-Blocks.html#Common-Blocks">Common Blocks</a>,
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Up: <a rel="up" accesskey="u" href="Variables.html#Variables">Variables</a>
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<hr>
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</div>
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<h3 class="section">4.5 Static Variables</h3>
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<p>Initialized static variables are represented by the ‘<samp><span class="samp">S</span></samp>’ and
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‘<samp><span class="samp">V</span></samp>’ symbol descriptors. ‘<samp><span class="samp">S</span></samp>’ means file scope static, and
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‘<samp><span class="samp">V</span></samp>’ means procedure scope static. One exception: in XCOFF, IBM's
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xlc compiler always uses ‘<samp><span class="samp">V</span></samp>’, and whether it is file scope or not
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is distinguished by whether the stab is located within a function.
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<!-- This is probably not worth mentioning; it is only true on the sparc -->
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<!-- for `double' variables which although declared const are actually in -->
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<!-- the data segment (the text segment can't guarantee 8 byte alignment). -->
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<!-- (although GCC -->
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<!-- 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can -->
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<!-- find the variables) -->
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<p><a name="index-N_005fSTSYM-37"></a><a name="index-N_005fLCSYM-38"></a><a name="index-N_005fFUN_002c-for-variables-39"></a><a name="index-N_005fROSYM-40"></a>In a.out files, <code>N_STSYM</code> means the data section, <code>N_FUN</code>
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means the text section, and <code>N_LCSYM</code> means the bss section. For
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those systems with a read-only data section separate from the text
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section (Solaris), <code>N_ROSYM</code> means the read-only data section.
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<p>For example, the source lines:
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<pre class="example"> static const int var_const = 5;
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static int var_init = 2;
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static int var_noinit;
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</pre>
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<p class="noindent">yield the following stabs:
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<pre class="example"> .stabs "var_const:S1",36,0,0,_var_const # <span class="roman">36 is N_FUN</span>
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...
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.stabs "var_init:S1",38,0,0,_var_init # <span class="roman">38 is N_STSYM</span>
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...
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.stabs "var_noinit:S1",40,0,0,_var_noinit # <span class="roman">40 is N_LCSYM</span>
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</pre>
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<p><a name="index-C_005fSTSYM-41"></a><a name="index-C_005fBSTAT-42"></a><a name="index-C_005fESTAT-43"></a>In XCOFF files, the stab type need not indicate the section;
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<code>C_STSYM</code> can be used for all statics. Also, each static variable
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is enclosed in a static block. A <code>C_BSTAT</code> (emitted with a
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‘<samp><span class="samp">.bs</span></samp>’ assembler directive) symbol begins the static block; its
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value is the symbol number of the csect symbol whose value is the
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address of the static block, its section is the section of the variables
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in that static block, and its name is ‘<samp><span class="samp">.bs</span></samp>’. A <code>C_ESTAT</code>
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(emitted with a ‘<samp><span class="samp">.es</span></samp>’ assembler directive) symbol ends the static
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block; its name is ‘<samp><span class="samp">.es</span></samp>’ and its value and section are ignored.
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<p>In ECOFF files, the storage class is used to specify the section, so the
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stab type need not indicate the section.
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<p>In ELF files, for the SunPRO compiler version 2.0.1, symbol descriptor
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‘<samp><span class="samp">S</span></samp>’ means that the address is absolute (the linker relocates it)
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and symbol descriptor ‘<samp><span class="samp">V</span></samp>’ means that the address is relative to the
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start of the relevant section for that compilation unit. SunPRO has
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plans to have the linker stop relocating stabs; I suspect that their the
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debugger gets the address from the corresponding ELF (not stab) symbol.
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I'm not sure how to find which symbol of that name is the right one.
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The clean way to do all this would be to have the value of a symbol
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descriptor ‘<samp><span class="samp">S</span></samp>’ symbol be an offset relative to the start of the
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file, just like everything else, but that introduces obvious
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compatibility problems. For more information on linker stab relocation,
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See <a href="ELF-Linker-Relocation.html#ELF-Linker-Relocation">ELF Linker Relocation</a>.
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</body></html>
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