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<h3 class="section">10.15 Operating System Auxiliary Information</h3>

<p><a name="index-OS-information-613"></a>
<span class="sc">gdb</span> provides interfaces to useful OS facilities that can help
you debug your program.

   <p><a name="index-g_t_0040code_007bptrace_007d-system-call-614"></a><a name="index-g_t_0040code_007bstruct-user_007d-contents-615"></a>When <span class="sc">gdb</span> runs on a <dfn>Posix system</dfn> (such as GNU or Unix
machines), it interfaces with the inferior via the <code>ptrace</code>
system call.  The operating system creates a special sata structure,
called <code>struct user</code>, for this interface.  You can use the
command <code>info udot</code> to display the contents of this data
structure.

     <dl>
<dt><code>info udot</code><dd><a name="index-info-udot-616"></a>Display the contents of the <code>struct user</code> maintained by the OS
kernel for the program being debugged.  <span class="sc">gdb</span> displays the
contents of <code>struct user</code> as a list of hex numbers, similar to
the <code>examine</code> command. 
</dl>

   <p><a name="index-auxiliary-vector-617"></a><a name="index-vector_002c-auxiliary-618"></a>Some operating systems supply an <dfn>auxiliary vector</dfn> to programs at
startup.  This is akin to the arguments and environment that you
specify for a program, but contains a system-dependent variety of
binary values that tell system libraries important details about the
hardware, operating system, and process.  Each value's purpose is
identified by an integer tag; the meanings are well-known but system-specific. 
Depending on the configuration and operating system facilities,
<span class="sc">gdb</span> may be able to show you this information.  For remote
targets, this functionality may further depend on the remote stub's
support of the &lsquo;<samp><span class="samp">qXfer:auxv:read</span></samp>&rsquo; packet, see
<a href="qXfer-auxiliary-vector-read.html#qXfer-auxiliary-vector-read">qXfer auxiliary vector read</a>.

     
<a name="index-info-auxv-619"></a>
<dl><dt><code>info auxv</code><dd>Display the auxiliary vector of the inferior, which can be either a
live process or a core dump file.  <span class="sc">gdb</span> prints each tag value
numerically, and also shows names and text descriptions for recognized
tags.  Some values in the vector are numbers, some bit masks, and some
pointers to strings or other data.  <span class="sc">gdb</span> displays each value in the
most appropriate form for a recognized tag, and in hexadecimal for
an unrecognized tag. 
</dl>

   <p>On some targets, <span class="sc">gdb</span> can access operating-system-specific information
and display it to user, without interpretation.  For remote targets,
this functionality depends on the remote stub's support of the
&lsquo;<samp><span class="samp">qXfer:osdata:read</span></samp>&rsquo; packet, see <a href="qXfer-osdata-read.html#qXfer-osdata-read">qXfer osdata read</a>.

     
<a name="index-info-os-620"></a>
<dl><dt><code>info os</code><dd>List the types of OS information available for the target.  If the
target does not return a list of possible types, this command will
report an error.

     <p><a name="index-info-os-processes-621"></a><br><dt><code>info os processes</code><dd>Display the list of processes on the target.  For each process,
<span class="sc">gdb</span> prints the process identifier, the name of the user, and
the command corresponding to the process. 
</dl>

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