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<table class="head">
<tr>
<td class="head-ltitle">STAB(5)</td>
<td class="head-vol">File Formats Manual</td>
<td class="head-rtitle">STAB(5)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">stab</code> — <span class="Nd">symbol
table types</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
<<a class="In">stab.h</a>></code></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The file <code class="In"><<a class="In">stab.h</a>></code>
defines some of the symbol table <var class="Fa">n_type</var> field values
for a.out files. These are the types for permanent symbols (i.e., not local
labels, etc.) used by the old debugger <i class="Em">sdb</i> and the
Berkeley Pascal compiler <a class="Xr">pc(1)</a>. Symbol table entries can
be produced by the <span class="Pa">.stabs</span> assembler directive. This
allows one to specify a double-quote delimited name, a symbol type, one char
and one short of information about the symbol, and an unsigned long (usually
an address). To avoid having to produce an explicit label for the address
field, the <span class="Pa">.stabd</span> directive can be used to
implicitly address the current location. If no name is needed, symbol table
entries can be generated using the <span class="Pa">.stabn</span> directive.
The loader promises to preserve the order of symbol table entries produced
by <span class="Pa">.stab</span> directives. As described in
<a class="Xr">a.out(5)</a>, an element of the symbol table consists of the
following structure:</p>
<div class="Bd Pp Li">
<pre>/*
* Format of a symbol table entry.
*/
struct nlist {
union {
const char *n_name; /* for use when in-core */
long n_strx; /* index into file string table */
} n_un;
unsigned char n_type; /* type flag */
char n_other; /* unused */
short n_desc; /* see struct desc, below */
unsigned n_value; /* address or offset or line */
};</pre>
</div>
<p class="Pp">The low bits of the <var class="Fa">n_type</var> field are used to
place a symbol into at most one segment, according to the following masks,
defined in <code class="In"><<a class="In">a.out.h</a>></code>. A
symbol can be in none of these segments by having none of these segment bits
set.</p>
<div class="Bd Pp Li">
<pre>/*
* Simple values for n_type.
*/
#define N_UNDF 0x0 /* undefined */
#define N_ABS 0x2 /* absolute */
#define N_TEXT 0x4 /* text */
#define N_DATA 0x6 /* data */
#define N_BSS 0x8 /* bss */
#define N_EXT 01 /* external bit, or'ed in */</pre>
</div>
<p class="Pp">The <var class="Fa">n_value</var> field of a symbol is relocated
by the linker, <a class="Xr">ld(1)</a> as an address within the appropriate
segment. <var class="Fa">N_value</var> fields of symbols not in any segment
are unchanged by the linker. In addition, the linker will discard certain
symbols, according to rules of its own, unless the
<var class="Fa">n_type</var> field has one of the following bits set:</p>
<div class="Bd Pp Li">
<pre>/*
* Other permanent symbol table entries have some of the N_STAB bits set.
* These are given in <stab.h>
*/
#define N_STAB 0xe0 /* if any of these bits set, don't discard */</pre>
</div>
<p class="Pp">This allows up to 112 (7 ∗ 16) symbol types, split between
the various segments. Some of these have already been claimed. The old
symbolic debugger, <i class="Em">sdb</i>, uses the following n_type
values:</p>
<div class="Bd Pp Li">
<pre>#define N_GSYM 0x20 /* global symbol: name,,0,type,0 */
#define N_FNAME 0x22 /* procedure name (f77 kludge): name,,0 */
#define N_FUN 0x24 /* procedure: name,,0,linenumber,address */
#define N_STSYM 0x26 /* static symbol: name,,0,type,address */
#define N_LCSYM 0x28 /* .lcomm symbol: name,,0,type,address */
#define N_RSYM 0x40 /* register sym: name,,0,type,register */
#define N_SLINE 0x44 /* src line: 0,,0,linenumber,address */
#define N_SSYM 0x60 /* structure elt: name,,0,type,struct_offset */
#define N_SO 0x64 /* source file name: name,,0,0,address */
#define N_LSYM 0x80 /* local sym: name,,0,type,offset */
#define N_SOL 0x84 /* #included file name: name,,0,0,address */
#define N_PSYM 0xa0 /* parameter: name,,0,type,offset */
#define N_ENTRY 0xa4 /* alternate entry: name,linenumber,address */
#define N_LBRAC 0xc0 /* left bracket: 0,,0,nesting level,address */
#define N_RBRAC 0xe0 /* right bracket: 0,,0,nesting level,address */
#define N_BCOMM 0xe2 /* begin common: name,, */
#define N_ECOMM 0xe4 /* end common: name,, */
#define N_ECOML 0xe8 /* end common (local name): ,,address */
#define N_LENG 0xfe /* second stab entry with length information */</pre>
</div>
<p class="Pp" id="Sdb">where the comments give <i class="Em">sdb</i>
conventional use for <span class="Pa">.stab</span> <var class="Fa">s</var>
and the <var class="Fa">n_name</var>, <var class="Fa">n_other</var>,
<var class="Fa">n_desc</var>, and <var class="Fa">n_value</var> fields of
the given <var class="Fa">n_type</var>.
<a class="permalink" href="#Sdb"><i class="Em">Sdb</i></a> uses the
<var class="Fa">n_desc</var> field to hold a type specifier in the form used
by the Portable C Compiler, <a class="Xr">cc(1)</a>; see the header file
<span class="Pa">pcc.h</span> for details on the format of these type
values.</p>
<p class="Pp">The Berkeley Pascal compiler, <a class="Xr">pc(1)</a>, uses the
following <var class="Fa">n_type</var> value:</p>
<div class="Bd Pp Li">
<pre>#define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */</pre>
</div>
<p class="Pp">and uses the following subtypes to do type checking across
separately compiled files:</p>
<div class="Bd Pp Bd-indent">
<pre>1 source file name
2 included file name
3 global label
4 global constant
5 global type
6 global variable
7 global function
8 global procedure
9 external function
10 external procedure
11 library variable
12 library routine</pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">as(1)</a>, <a class="Xr">ld(1)</a>,
<a class="Xr">a.out(5)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">stab</code> file appeared in
<span class="Ux">4.0BSD</span>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="BUGS"><a class="permalink" href="#BUGS">BUGS</a></h1>
<p class="Pp">More basic types are needed.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">June 10, 2010</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
