huangmeng
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asj_pe_project


			
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Files"></a>
<div class="header">
<p>
Next: <a href="File-Caching.html#File-Caching" accesskey="n" rel="next">File Caching</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Commands-to-Specify-Files"></a>
<h3 class="section">18.1 Commands to Specify Files</h3>

<a name="index-symbol-table"></a>
<a name="index-core-dump-file"></a>

<p>You may want to specify executable and core dump file names.  The usual
way to do this is at start-up time, using the arguments to
<small>GDB</small>&rsquo;s start-up commands (see <a href="Invocation.html#Invocation">Getting In and
Out of <small>GDB</small></a>).
</p>
<p>Occasionally it is necessary to change to a different file during a
<small>GDB</small> session.  Or you may run <small>GDB</small> and forget to
specify a file you want to use.  Or you are debugging a remote target
via <code>gdbserver</code> (see <a href="Server.html#Server">Using the <code>gdbserver</code>
Program</a>).  In these situations the <small>GDB</small> commands to specify
new files are useful.
</p>
<dl compact="compact">
<dd><a name="index-executable-file"></a>
<a name="index-file"></a>
</dd>
<dt><code>file <var>filename</var></code></dt>
<dd><p>Use <var>filename</var> as the program to be debugged.  It is read for its
symbols and for the contents of pure memory.  It is also the program
executed when you use the <code>run</code> command.  If you do not specify a
directory and the file is not found in the <small>GDB</small> working directory,
<small>GDB</small> uses the environment variable <code>PATH</code> as a list of
directories to search, just as the shell does when looking for a program
to run.  You can change the value of this variable, for both <small>GDB</small>
and your program, using the <code>path</code> command.
</p>
<a name="index-unlinked-object-files"></a>
<a name="index-patching-object-files"></a>
<p>You can load unlinked object <samp>.o</samp> files into <small>GDB</small> using
the <code>file</code> command.  You will not be able to &ldquo;run&rdquo; an object
file, but you can disassemble functions and inspect variables.  Also,
if the underlying BFD functionality supports it, you could use
<kbd>gdb -write</kbd> to patch object files using this technique.  Note
that <small>GDB</small> can neither interpret nor modify relocations in this
case, so branches and some initialized variables will appear to go to
the wrong place.  But this feature is still handy from time to time.
</p>
</dd>
<dt><code>file</code></dt>
<dd><p><code>file</code> with no argument makes <small>GDB</small> discard any information it
has on both executable file and the symbol table.
</p>
<a name="index-exec_002dfile"></a>
</dd>
<dt><code>exec-file <span class="roman">[</span> <var>filename</var> <span class="roman">]</span></code></dt>
<dd><p>Specify that the program to be run (but not the symbol table) is found
in <var>filename</var>.  <small>GDB</small> searches the environment variable <code>PATH</code>
if necessary to locate your program.  Omitting <var>filename</var> means to
discard information on the executable file.
</p>
<a name="index-symbol_002dfile"></a>
</dd>
<dt><code>symbol-file <span class="roman">[</span> <var>filename</var> <span class="roman">[</span> -o <var>offset</var> <span class="roman">]]</span></code></dt>
<dd><p>Read symbol table information from file <var>filename</var>.  <code>PATH</code> is
searched when necessary.  Use the <code>file</code> command to get both symbol
table and program to run from the same file.
</p>
<p>If an optional <var>offset</var> is specified, it is added to the start
address of each section in the symbol file.  This is useful if the
program is relocated at runtime, such as the Linux kernel with kASLR
enabled.
</p>
<p><code>symbol-file</code> with no argument clears out <small>GDB</small> information on your
program&rsquo;s symbol table.
</p>
<p>The <code>symbol-file</code> command causes <small>GDB</small> to forget the contents of
some breakpoints and auto-display expressions.  This is because they may
contain pointers to the internal data recording symbols and data types,
which are part of the old symbol table data being discarded inside
<small>GDB</small>.
</p>
<p><code>symbol-file</code> does not repeat if you press <tt class="key">RET</tt> again after
executing it once.
</p>
<p>When <small>GDB</small> is configured for a particular environment, it
understands debugging information in whatever format is the standard
generated for that environment; you may use either a <small>GNU</small> compiler, or
other compilers that adhere to the local conventions.
Best results are usually obtained from <small>GNU</small> compilers; for example,
using <code><small>GCC</small></code> you can generate debugging information for
optimized code.
</p>
<p>For most kinds of object files, with the exception of old SVR3 systems
using COFF, the <code>symbol-file</code> command does not normally read the
symbol table in full right away.  Instead, it scans the symbol table
quickly to find which source files and which symbols are present.  The
details are read later, one source file at a time, as they are needed.
</p>
<p>The purpose of this two-stage reading strategy is to make <small>GDB</small>
start up faster.  For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular source
file are being read.  (The <code>set verbose</code> command can turn these
pauses into messages if desired.  See <a href="Messages_002fWarnings.html#Messages_002fWarnings">Optional
Warnings and Messages</a>.)
</p>
<p>We have not implemented the two-stage strategy for COFF yet.  When the
symbol table is stored in COFF format, <code>symbol-file</code> reads the
symbol table data in full right away.  Note that &ldquo;stabs-in-COFF&rdquo;
still does the two-stage strategy, since the debug info is actually
in stabs format.
</p>
<a name="index-readnow"></a>
<a name="index-reading-symbols-immediately"></a>
<a name="index-symbols_002c-reading-immediately"></a>
</dd>
<dt><code>symbol-file <span class="roman">[</span> -readnow <span class="roman">]</span> <var>filename</var></code></dt>
<dt><code>file <span class="roman">[</span> -readnow <span class="roman">]</span> <var>filename</var></code></dt>
<dd><p>You can override the <small>GDB</small> two-stage strategy for reading symbol
tables by using the &lsquo;<samp>-readnow</samp>&rsquo; option with any of the commands that
load symbol table information, if you want to be sure <small>GDB</small> has the
entire symbol table available.
</p>
<a name="index-_002dreadnever_002c-option-for-symbol_002dfile-command"></a>
<a name="index-never-read-symbols"></a>
<a name="index-symbols_002c-never-read"></a>
</dd>
<dt><code>symbol-file <span class="roman">[</span> -readnever <span class="roman">]</span> <var>filename</var></code></dt>
<dt><code>file <span class="roman">[</span> -readnever <span class="roman">]</span> <var>filename</var></code></dt>
<dd><p>You can instruct <small>GDB</small> to never read the symbolic information
contained in <var>filename</var> by using the &lsquo;<samp>-readnever</samp>&rsquo; option.
See <a href="File-Options.html#g_t_002d_002dreadnever">--readnever</a>.
</p>

<a name="index-core_002dfile"></a>
</dd>
<dt><code>core-file <span class="roman">[</span><var>filename</var><span class="roman">]</span></code></dt>
<dt><code>core</code></dt>
<dd><p>Specify the whereabouts of a core dump file to be used as the &ldquo;contents
of memory&rdquo;.  Traditionally, core files contain only some parts of the
address space of the process that generated them; <small>GDB</small> can access the
executable file itself for other parts.
</p>
<p><code>core-file</code> with no argument specifies that no core file is
to be used.
</p>
<p>Note that the core file is ignored when your program is actually running
under <small>GDB</small>.  So, if you have been running your program and you
wish to debug a core file instead, you must kill the subprocess in which
the program is running.  To do this, use the <code>kill</code> command
(see <a href="Kill-Process.html#Kill-Process">Killing the Child Process</a>).
</p>
<a name="index-add_002dsymbol_002dfile"></a>
<a name="index-dynamic-linking"></a>
</dd>
<dt><code>add-symbol-file <var>filename</var> <span class="roman">[</span> -readnow <span class="roman">|</span> -readnever <span class="roman">]</span> <span class="roman">[</span> -o <var>offset</var> <span class="roman">]</span> <span class="roman">[</span> <var>textaddress</var> <span class="roman">]</span> <span class="roman">[</span> -s <var>section</var> <var>address</var> &hellip; <span class="roman">]</span></code></dt>
<dd><p>The <code>add-symbol-file</code> command reads additional symbol table
information from the file <var>filename</var>.  You would use this command
when <var>filename</var> has been dynamically loaded (by some other means)
into the program that is running.  The <var>textaddress</var> parameter gives
the memory address at which the file&rsquo;s text section has been loaded.
You can additionally specify the base address of other sections using
an arbitrary number of &lsquo;<samp>-s <var>section</var> <var>address</var></samp>&rsquo; pairs.
If a section is omitted, <small>GDB</small> will use its default addresses
as found in <var>filename</var>.  Any <var>address</var> or <var>textaddress</var>
can be given as an expression.
</p>
<p>If an optional <var>offset</var> is specified, it is added to the start
address of each section, except those for which the address was
specified explicitly.
</p>
<p>The symbol table of the file <var>filename</var> is added to the symbol table
originally read with the <code>symbol-file</code> command.  You can use the
<code>add-symbol-file</code> command any number of times; the new symbol data
thus read is kept in addition to the old.
</p>
<p>Changes can be reverted using the command <code>remove-symbol-file</code>.
</p>
<a name="index-relocatable-object-files_002c-reading-symbols-from"></a>
<a name="index-object-files_002c-relocatable_002c-reading-symbols-from"></a>
<a name="index-reading-symbols-from-relocatable-object-files"></a>
<a name="index-symbols_002c-reading-from-relocatable-object-files"></a>
<a name="index-_002eo-files_002c-reading-symbols-from"></a>
<p>Although <var>filename</var> is typically a shared library file, an
executable file, or some other object file which has been fully
relocated for loading into a process, you can also load symbolic
information from relocatable <samp>.o</samp> files, as long as:
</p>
<ul>
<li> the file&rsquo;s symbolic information refers only to linker symbols defined in
that file, not to symbols defined by other object files,
</li><li> every section the file&rsquo;s symbolic information refers to has actually
been loaded into the inferior, as it appears in the file, and
</li><li> you can determine the address at which every section was loaded, and
provide these to the <code>add-symbol-file</code> command.
</li></ul>

<p>Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems
typically make the requirements above easy to meet.  However, it&rsquo;s
important to recognize that many native systems use complex link
procedures (<code>.linkonce</code> section factoring and C<tt>++</tt> constructor table
assembly, for example) that make the requirements difficult to meet.  In
general, one cannot assume that using <code>add-symbol-file</code> to read a
relocatable object file&rsquo;s symbolic information will have the same effect
as linking the relocatable object file into the program in the normal
way.
</p>
<p><code>add-symbol-file</code> does not repeat if you press <tt class="key">RET</tt> after using it.
</p>
<a name="index-remove_002dsymbol_002dfile"></a>
</dd>
<dt><code>remove-symbol-file <var>filename</var></code></dt>
<dt><code>remove-symbol-file -a <var>address</var></code></dt>
<dd><p>Remove a symbol file added via the <code>add-symbol-file</code> command.  The
file to remove can be identified by its <var>filename</var> or by an <var>address</var>
that lies within the boundaries of this symbol file in memory.  Example:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480
add symbol table from file &quot;/home/user/gdb/mylib.so&quot; at
    .text_addr = 0x7ffff7ff9480
(y or n) y
Reading symbols from /home/user/gdb/mylib.so...
(gdb) remove-symbol-file -a 0x7ffff7ff9480
Remove symbol table from file &quot;/home/user/gdb/mylib.so&quot;? (y or n) y
(gdb)
</pre></div>


<p><code>remove-symbol-file</code> does not repeat if you press <tt class="key">RET</tt> after using it.
</p>
<a name="index-add_002dsymbol_002dfile_002dfrom_002dmemory"></a>
<a name="index-syscall-DSO"></a>
<a name="index-load-symbols-from-memory"></a>
</dd>
<dt><code>add-symbol-file-from-memory <var>address</var></code></dt>
<dd><p>Load symbols from the given <var>address</var> in a dynamically loaded
object file whose image is mapped directly into the inferior&rsquo;s memory.
For example, the Linux kernel maps a <code>syscall DSO</code> into each
process&rsquo;s address space; this DSO provides kernel-specific code for
some system calls.  The argument can be any expression whose
evaluation yields the address of the file&rsquo;s shared object file header.
For this command to work, you must have used <code>symbol-file</code> or
<code>exec-file</code> commands in advance.
</p>
<a name="index-section"></a>
</dd>
<dt><code>section <var>section</var> <var>addr</var></code></dt>
<dd><p>The <code>section</code> command changes the base address of the named
<var>section</var> of the exec file to <var>addr</var>.  This can be used if the
exec file does not contain section addresses, (such as in the
<code>a.out</code> format), or when the addresses specified in the file
itself are wrong.  Each section must be changed separately.  The
<code>info files</code> command, described below, lists all the sections and
their addresses.
</p>
<a name="index-info-files"></a>
<a name="index-info-target"></a>
</dd>
<dt><code>info files</code></dt>
<dt><code>info target</code></dt>
<dd><p><code>info files</code> and <code>info target</code> are synonymous; both print the
current target (see <a href="Targets.html#Targets">Specifying a Debugging Target</a>),
including the names of the executable and core dump files currently in
use by <small>GDB</small>, and the files from which symbols were loaded.  The
command <code>help target</code> lists all possible targets rather than
current ones.
</p>
<a name="index-maint-info-sections"></a>
</dd>
<dt><code>maint info sections</code></dt>
<dd><p>Another command that can give you extra information about program sections
is <code>maint info sections</code>.  In addition to the section information
displayed by <code>info files</code>, this command displays the flags and file
offset of each section in the executable and core dump files.  In addition,
<code>maint info sections</code> provides the following command options (which
may be arbitrarily combined):
</p>
<dl compact="compact">
<dt><code>ALLOBJ</code></dt>
<dd><p>Display sections for all loaded object files, including shared libraries.
</p></dd>
<dt><code><var>sections</var></code></dt>
<dd><p>Display info only for named <var>sections</var>.
</p></dd>
<dt><code><var>section-flags</var></code></dt>
<dd><p>Display info only for sections for which <var>section-flags</var> are true.
The section flags that <small>GDB</small> currently knows about are:
</p><dl compact="compact">
<dt><code>ALLOC</code></dt>
<dd><p>Section will have space allocated in the process when loaded.
Set for all sections except those containing debug information.
</p></dd>
<dt><code>LOAD</code></dt>
<dd><p>Section will be loaded from the file into the child process memory.
Set for pre-initialized code and data, clear for <code>.bss</code> sections.
</p></dd>
<dt><code>RELOC</code></dt>
<dd><p>Section needs to be relocated before loading.
</p></dd>
<dt><code>READONLY</code></dt>
<dd><p>Section cannot be modified by the child process.
</p></dd>
<dt><code>CODE</code></dt>
<dd><p>Section contains executable code only.
</p></dd>
<dt><code>DATA</code></dt>
<dd><p>Section contains data only (no executable code).
</p></dd>
<dt><code>ROM</code></dt>
<dd><p>Section will reside in ROM.
</p></dd>
<dt><code>CONSTRUCTOR</code></dt>
<dd><p>Section contains data for constructor/destructor lists.
</p></dd>
<dt><code>HAS_CONTENTS</code></dt>
<dd><p>Section is not empty.
</p></dd>
<dt><code>NEVER_LOAD</code></dt>
<dd><p>An instruction to the linker to not output the section.
</p></dd>
<dt><code>COFF_SHARED_LIBRARY</code></dt>
<dd><p>A notification to the linker that the section contains
COFF shared library information.
</p></dd>
<dt><code>IS_COMMON</code></dt>
<dd><p>Section contains common symbols.
</p></dd>
</dl>
</dd>
</dl>
<a name="index-set-trust_002dreadonly_002dsections"></a>
<a name="index-read_002donly-sections"></a>
</dd>
<dt><code>set trust-readonly-sections on</code></dt>
<dd><p>Tell <small>GDB</small> that readonly sections in your object file
really are read-only (i.e. that their contents will not change).
In that case, <small>GDB</small> can fetch values from these sections
out of the object file, rather than from the target program.
For some targets (notably embedded ones), this can be a significant
enhancement to debugging performance.
</p>
<p>The default is off.
</p>
</dd>
<dt><code>set trust-readonly-sections off</code></dt>
<dd><p>Tell <small>GDB</small> not to trust readonly sections.  This means that
the contents of the section might change while the program is running,
and must therefore be fetched from the target when needed.
</p>
</dd>
<dt><code>show trust-readonly-sections</code></dt>
<dd><p>Show the current setting of trusting readonly sections.
</p></dd>
</dl>

<p>All file-specifying commands allow both absolute and relative file names
as arguments.  <small>GDB</small> always converts the file name to an absolute file
name and remembers it that way.
</p>
<a name="index-shared-libraries"></a>
<a name="Shared-Libraries"></a><p><small>GDB</small> supports <small>GNU</small>/Linux, MS-Windows, SunOS,
Darwin/Mach-O, SVr4, IBM RS/6000 AIX, QNX Neutrino, FDPIC (FR-V), and
DSBT (TIC6X) shared libraries.
</p>
<p>On MS-Windows <small>GDB</small> must be linked with the Expat library to support
shared libraries.  See <a href="Requirements.html#Expat">Expat</a>.
</p>
<p><small>GDB</small> automatically loads symbol definitions from shared libraries
when you use the <code>run</code> command, or when you examine a core file.
(Before you issue the <code>run</code> command, <small>GDB</small> does not understand
references to a function in a shared library, however&mdash;unless you are
debugging a core file).
</p>

<p>There are times, however, when you may wish to not automatically load
symbol definitions from shared libraries, such as when they are
particularly large or there are many of them.
</p>
<p>To control the automatic loading of shared library symbols, use the
commands:
</p>
<dl compact="compact">
<dd><a name="index-set-auto_002dsolib_002dadd"></a>
</dd>
<dt><code>set auto-solib-add <var>mode</var></code></dt>
<dd><p>If <var>mode</var> is <code>on</code>, symbols from all shared object libraries
will be loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic linker
informs <small>GDB</small> that a new library has been loaded.  If <var>mode</var>
is <code>off</code>, symbols must be loaded manually, using the
<code>sharedlibrary</code> command.  The default value is <code>on</code>.
</p>
<a name="index-memory-used-for-symbol-tables"></a>
<p>If your program uses lots of shared libraries with debug info that
takes large amounts of memory, you can decrease the <small>GDB</small>
memory footprint by preventing it from automatically loading the
symbols from shared libraries.  To that end, type <kbd>set
auto-solib-add off</kbd> before running the inferior, then load each
library whose debug symbols you do need with <kbd>sharedlibrary
<var>regexp</var></kbd>, where <var>regexp</var> is a regular expression that matches
the libraries whose symbols you want to be loaded.
</p>
<a name="index-show-auto_002dsolib_002dadd"></a>
</dd>
<dt><code>show auto-solib-add</code></dt>
<dd><p>Display the current autoloading mode.
</p></dd>
</dl>

<a name="index-load-shared-library"></a>
<p>To explicitly load shared library symbols, use the <code>sharedlibrary</code>
command:
</p>
<dl compact="compact">
<dd><a name="index-info-sharedlibrary"></a>
<a name="index-info-share"></a>
</dd>
<dt><code>info share <var>regex</var></code></dt>
<dt><code>info sharedlibrary <var>regex</var></code></dt>
<dd><p>Print the names of the shared libraries which are currently loaded
that match <var>regex</var>.  If <var>regex</var> is omitted then print
all shared libraries that are loaded.
</p>
<a name="index-info-dll"></a>
</dd>
<dt><code>info dll <var>regex</var></code></dt>
<dd><p>This is an alias of <code>info sharedlibrary</code>.
</p>
<a name="index-sharedlibrary"></a>
<a name="index-share"></a>
</dd>
<dt><code>sharedlibrary <var>regex</var></code></dt>
<dt><code>share <var>regex</var></code></dt>
<dd><p>Load shared object library symbols for files matching a
Unix regular expression.
As with files loaded automatically, it only loads shared libraries
required by your program for a core file or after typing <code>run</code>.  If
<var>regex</var> is omitted all shared libraries required by your program are
loaded.
</p>
</dd>
<dt><code>nosharedlibrary</code></dt>
<dd><a name="index-nosharedlibrary"></a>
<a name="index-unload-symbols-from-shared-libraries"></a>
<p>Unload all shared object library symbols.  This discards all symbols
that have been loaded from all shared libraries.  Symbols from shared
libraries that were loaded by explicit user requests are not
discarded.
</p></dd>
</dl>

<p>Sometimes you may wish that <small>GDB</small> stops and gives you control
when any of shared library events happen.  The best way to do this is
to use <code>catch load</code> and <code>catch unload</code> (see <a href="Set-Catchpoints.html#Set-Catchpoints">Set Catchpoints</a>).
</p>
<p><small>GDB</small> also supports the <code>set stop-on-solib-events</code>
command for this.  This command exists for historical reasons.  It is
less useful than setting a catchpoint, because it does not allow for
conditions or commands as a catchpoint does.
</p>
<dl compact="compact">
<dt><code>set stop-on-solib-events</code></dt>
<dd><a name="index-set-stop_002don_002dsolib_002devents"></a>
<p>This command controls whether <small>GDB</small> should give you control
when the dynamic linker notifies it about some shared library event.
The most common event of interest is loading or unloading of a new
shared library.
</p>
</dd>
<dt><code>show stop-on-solib-events</code></dt>
<dd><a name="index-show-stop_002don_002dsolib_002devents"></a>
<p>Show whether <small>GDB</small> stops and gives you control when shared
library events happen.
</p></dd>
</dl>

<p>Shared libraries are also supported in many cross or remote debugging
configurations.  <small>GDB</small> needs to have access to the target&rsquo;s libraries;
this can be accomplished either by providing copies of the libraries
on the host system, or by asking <small>GDB</small> to automatically retrieve the
libraries from the target.  If copies of the target libraries are
provided, they need to be the same as the target libraries, although the
copies on the target can be stripped as long as the copies on the host are
not.
</p>
<a name="index-where-to-look-for-shared-libraries"></a>
<p>For remote debugging, you need to tell <small>GDB</small> where the target
libraries are, so that it can load the correct copies&mdash;otherwise, it
may try to load the host&rsquo;s libraries.  <small>GDB</small> has two variables
to specify the search directories for target libraries.
</p>
<dl compact="compact">
<dd><a name="index-prefix-for-executable-and-shared-library-file-names"></a>
<a name="index-system-root_002c-alternate"></a>
<a name="index-set-solib_002dabsolute_002dprefix"></a>
<a name="index-set-sysroot"></a>
</dd>
<dt><code>set sysroot <var>path</var></code></dt>
<dd><p>Use <var>path</var> as the system root for the program being debugged.  Any
absolute shared library paths will be prefixed with <var>path</var>; many
runtime loaders store the absolute paths to the shared library in the
target program&rsquo;s memory.  When starting processes remotely, and when
attaching to already-running processes (local or remote), their
executable filenames will be prefixed with <var>path</var> if reported to
<small>GDB</small> as absolute by the operating system.  If you use
<code>set sysroot</code> to find executables and shared libraries, they need
to be laid out in the same way that they are on the target, with
e.g. a <samp>/bin</samp>, <samp>/lib</samp> and <samp>/usr/lib</samp> hierarchy under
<var>path</var>.
</p>
<p>If <var>path</var> starts with the sequence <samp>target:</samp> and the target
system is remote then <small>GDB</small> will retrieve the target binaries
from the remote system.  This is only supported when using a remote
target that supports the <code>remote get</code> command (see <a href="File-Transfer.html#File-Transfer">Sending files to a remote system</a>).  The part of <var>path</var>
following the initial <samp>target:</samp> (if present) is used as system
root prefix on the remote file system.  If <var>path</var> starts with the
sequence <samp>remote:</samp> this is converted to the sequence
<samp>target:</samp> by <code>set sysroot</code><a name="DOCF15" href="#FOOT15"><sup>15</sup></a>.  If you want
to specify a local system root using a directory that happens to be
named <samp>target:</samp> or <samp>remote:</samp>, you need to use some
equivalent variant of the name like <samp>./target:</samp>.
</p>
<p>For targets with an MS-DOS based filesystem, such as MS-Windows and
SymbianOS, <small>GDB</small> tries prefixing a few variants of the target
absolute file name with <var>path</var>.  But first, on Unix hosts,
<small>GDB</small> converts all backslash directory separators into forward
slashes, because the backslash is not a directory separator on Unix:
</p>
<div class="smallexample">
<pre class="smallexample">  c:\foo\bar.dll &rArr; c:/foo/bar.dll
</pre></div>

<p>Then, <small>GDB</small> attempts prefixing the target file name with
<var>path</var>, and looks for the resulting file name in the host file
system:
</p>
<div class="smallexample">
<pre class="smallexample">  c:/foo/bar.dll &rArr; /path/to/sysroot/c:/foo/bar.dll
</pre></div>

<p>If that does not find the binary, <small>GDB</small> tries removing
the &lsquo;<samp>:</samp>&rsquo; character from the drive spec, both for convenience, and,
for the case of the host file system not supporting file names with
colons:
</p>
<div class="smallexample">
<pre class="smallexample">  c:/foo/bar.dll &rArr; /path/to/sysroot/c/foo/bar.dll
</pre></div>

<p>This makes it possible to have a system root that mirrors a target
with more than one drive.  E.g., you may want to setup your local
copies of the target system shared libraries like so (note &lsquo;<samp>c</samp>&rsquo; vs
&lsquo;<samp>z</samp>&rsquo;):
</p>
<div class="smallexample">
<pre class="smallexample"> <samp>/path/to/sysroot/c/sys/bin/foo.dll</samp>
 <samp>/path/to/sysroot/c/sys/bin/bar.dll</samp>
 <samp>/path/to/sysroot/z/sys/bin/bar.dll</samp>
</pre></div>

<p>and point the system root at <samp>/path/to/sysroot</samp>, so that
<small>GDB</small> can find the correct copies of both
<samp>c:\sys\bin\foo.dll</samp>, and <samp>z:\sys\bin\bar.dll</samp>.
</p>
<p>If that still does not find the binary, <small>GDB</small> tries
removing the whole drive spec from the target file name:
</p>
<div class="smallexample">
<pre class="smallexample">  c:/foo/bar.dll &rArr; /path/to/sysroot/foo/bar.dll
</pre></div>

<p>This last lookup makes it possible to not care about the drive name,
if you don&rsquo;t want or need to.
</p>
<p>The <code>set solib-absolute-prefix</code> command is an alias for <code>set
sysroot</code>.
</p>
<a name="index-default-system-root"></a>
<a name="index-_002d_002dwith_002dsysroot"></a>
<p>You can set the default system root by using the configure-time
&lsquo;<samp>--with-sysroot</samp>&rsquo; option.  If the system root is inside
<small>GDB</small>&rsquo;s configured binary prefix (set with &lsquo;<samp>--prefix</samp>&rsquo; or
&lsquo;<samp>--exec-prefix</samp>&rsquo;), then the default system root will be updated
automatically if the installed <small>GDB</small> is moved to a new
location.
</p>
<a name="index-show-sysroot"></a>
</dd>
<dt><code>show sysroot</code></dt>
<dd><p>Display the current executable and shared library prefix.
</p>
<a name="index-set-solib_002dsearch_002dpath"></a>
</dd>
<dt><code>set solib-search-path <var>path</var></code></dt>
<dd><p>If this variable is set, <var>path</var> is a colon-separated list of
directories to search for shared libraries.  &lsquo;<samp>solib-search-path</samp>&rsquo;
is used after &lsquo;<samp>sysroot</samp>&rsquo; fails to locate the library, or if the
path to the library is relative instead of absolute.  If you want to
use &lsquo;<samp>solib-search-path</samp>&rsquo; instead of &lsquo;<samp>sysroot</samp>&rsquo;, be sure to set
&lsquo;<samp>sysroot</samp>&rsquo; to a nonexistent directory to prevent <small>GDB</small> from
finding your host&rsquo;s libraries.  &lsquo;<samp>sysroot</samp>&rsquo; is preferred; setting
it to a nonexistent directory may interfere with automatic loading
of shared library symbols.
</p>
<a name="index-show-solib_002dsearch_002dpath"></a>
</dd>
<dt><code>show solib-search-path</code></dt>
<dd><p>Display the current shared library search path.
</p>
<a name="index-DOS-file_002dname-semantics-of-file-names_002e"></a>
<a name="index-set-target_002dfile_002dsystem_002dkind-_0028unix_007cdos_002dbased_007cauto_0029"></a>
<a name="index-show-target_002dfile_002dsystem_002dkind"></a>
</dd>
<dt><code>set target-file-system-kind <var>kind</var></code></dt>
<dd><p>Set assumed file system kind for target reported file names.
</p>
<p>Shared library file names as reported by the target system may not
make sense as is on the system <small>GDB</small> is running on.  For
example, when remote debugging a target that has MS-DOS based file
system semantics, from a Unix host, the target may be reporting to
<small>GDB</small> a list of loaded shared libraries with file names such as
<samp>c:\Windows\kernel32.dll</samp>.  On Unix hosts, there&rsquo;s no concept of
drive letters, so the &lsquo;<samp>c:\</samp>&rsquo; prefix is not normally understood as
indicating an absolute file name, and neither is the backslash
normally considered a directory separator character.  In that case,
the native file system would interpret this whole absolute file name
as a relative file name with no directory components.  This would make
it impossible to point <small>GDB</small> at a copy of the remote target&rsquo;s
shared libraries on the host using <code>set sysroot</code>, and impractical
with <code>set solib-search-path</code>.  Setting
<code>target-file-system-kind</code> to <code>dos-based</code> tells <small>GDB</small>
to interpret such file names similarly to how the target would, and to
map them to file names valid on <small>GDB</small>&rsquo;s native file system
semantics.  The value of <var>kind</var> can be <code>&quot;auto&quot;</code>, in addition
to one of the supported file system kinds.  In that case, <small>GDB</small>
tries to determine the appropriate file system variant based on the
current target&rsquo;s operating system (see <a href="ABI.html#ABI">Configuring the
Current ABI</a>).  The supported file system settings are:
</p>
<dl compact="compact">
<dt><code>unix</code></dt>
<dd><p>Instruct <small>GDB</small> to assume the target file system is of Unix
kind.  Only file names starting the forward slash (&lsquo;<samp>/</samp>&rsquo;) character
are considered absolute, and the directory separator character is also
the forward slash.
</p>
</dd>
<dt><code>dos-based</code></dt>
<dd><p>Instruct <small>GDB</small> to assume the target file system is DOS based.
File names starting with either a forward slash, or a drive letter
followed by a colon (e.g., &lsquo;<samp>c:</samp>&rsquo;), are considered absolute, and
both the slash (&lsquo;<samp>/</samp>&rsquo;) and the backslash (&lsquo;<samp>\\</samp>&rsquo;) characters are
considered directory separators.
</p>
</dd>
<dt><code>auto</code></dt>
<dd><p>Instruct <small>GDB</small> to use the file system kind associated with the
target operating system (see <a href="ABI.html#ABI">Configuring the Current ABI</a>).
This is the default.
</p></dd>
</dl>
</dd>
</dl>

<a name="index-file-name-canonicalization"></a>
<a name="index-base-name-differences"></a>
<p>When processing file names provided by the user, <small>GDB</small>
frequently needs to compare them to the file names recorded in the
program&rsquo;s debug info.  Normally, <small>GDB</small> compares just the
<em>base names</em> of the files as strings, which is reasonably fast
even for very large programs.  (The base name of a file is the last
portion of its name, after stripping all the leading directories.)
This shortcut in comparison is based upon the assumption that files
cannot have more than one base name.  This is usually true, but
references to files that use symlinks or similar filesystem
facilities violate that assumption.  If your program records files
using such facilities, or if you provide file names to <small>GDB</small>
using symlinks etc., you can set <code>basenames-may-differ</code> to
<code>true</code> to instruct <small>GDB</small> to completely canonicalize each
pair of file names it needs to compare.  This will make file-name
comparisons accurate, but at a price of a significant slowdown.
</p>
<dl compact="compact">
<dt><code>set basenames-may-differ</code></dt>
<dd><a name="index-set-basenames_002dmay_002ddiffer"></a>
<p>Set whether a source file may have multiple base names.
</p>
</dd>
<dt><code>show basenames-may-differ</code></dt>
<dd><a name="index-show-basenames_002dmay_002ddiffer"></a>
<p>Show whether a source file may have multiple base names.
</p></dd>
</dl>

<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>

<h3><a name="FOOT15" href="#DOCF15">(15)</a></h3>
<p>Historically the
functionality to retrieve binaries from the remote system was
provided by prefixing <var>path</var> with <samp>remote:</samp></p>
</div>
<hr>
<div class="header">
<p>
Next: <a href="File-Caching.html#File-Caching" accesskey="n" rel="next">File Caching</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>


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