c_call.htm

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<title>The call Command</title>
<h1>call</h1>

<!--INDEX "call command" "execute subroutine" "argc argv" -->

The call command executes a subroutine.<p>

</dl><h2>Format</h2><dl><dd>

The format for the call command is:<p>

<pre>
call adr [-s str|val]..
</pre>

where:<p>

<table><tr><td>
adr	</td><td>is the address of the subroutine to be executed.
</td></tr><tr><td>
-s <i>str</i>	</td><td>is a string argument.
</td></tr><tr><td>
<i>val</i>	</td><td>is a value to be passed.
</td></tr></table>

The call command calls a function using the standard C calling
convention. The "-s <i>str</i>" 
and <i>val</i> options permit arguments to be passed to the subroutine.<p>


</dl><h2>Functional Description</h2><dl><dd>

The call command executes a downloaded subroutine, using a jalr instruction
to pass control to the specified address.
This does not affect the existing value of the saved
registers. Instead the subroutine is called directly from C code
without restoring the saved registers. Control returns to PMON
via the usual subroutine return mechanism. <p>

If the user specifies arguments,
these are passed using the standard C calling convention. If the
"-s" option is specified, the following argument is assumed to be
a string. In this case the address of the string is passed to the
subroutine. If a numerical value is specified in place of the "-s",
it will be evaluated according to the existing rules and passed
to the function. Up to five arguments may be passed.<p>

This command is usually used to provide a method of displaying
application-specific data structures. For example, if your application
has a complex, linked-list data structure, you might find it helpful
to add a function to your program that can display the structure. The
<i>call</i> command can then be used to invoke this function from the
PMON prompt at any time in the execution, even between two single-step
operations.<p>

Examples illustrating the use of the call command follow.<p>

<pre>
PMON> call prstat		Call the function whos name is 'prstat'.

PMON> call prrec a0020000+8	Call the function 'prrec' and pass it
				the value 0xa0020008 as the first argument.

PMON> call printf -s "hello world"
				Call the function printf and pass it the
				address of the string "hello world".
</pre>

</dl><h2>Files</h2><dl><dd>
The call command is located in <a href="../mon/call.c">mon/call.c</a>.

</dl><h2>See Also</h2><dl><dd>
<a href="c_g.htm">g command</a>
</dl><p><hr>
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