This file is indexed.

/usr/share/systemtap/tapset/context-unwind.stp is in systemtap-common 1.6-1ubuntu1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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// context-unwind tapset
// Copyright (C) 2005-2010 Red Hat Inc.
// Copyright (C) 2006 Intel Corporation.
//
// This file is part of systemtap, and is free software.  You can
// redistribute it and/or modify it under the terms of the GNU General
// Public License (GPL); either version 2, or (at your option) any
// later version.
// <tapsetdescription>
// Context functions provide additional information about where an event occurred. These functions can 
//provide information such as a backtrace to where the event occurred and the current register values for the 
//processor.
// </tapsetdescription>
%{
#ifndef STP_NEED_UNWIND_DATA
#define STP_NEED_UNWIND_DATA 1
#endif
#ifndef STP_NEED_SYMBOL_DATA
#define STP_NEED_SYMBOL_DATA 1
#endif
%}

/**
 *  sfunction print_backtrace - Print stack back trace
 * 
 *  Description: This function isEquivalent to print_stack(backtrace()), 
 *  except that deeper stack nesting may be supported.
 *  The function does not return a value.
 */
function print_backtrace () %{
	if (CONTEXT->regs && ! (CONTEXT->regflags & _STP_REGS_USER_FLAG)) {
		_stp_stack_print(CONTEXT->regs, _STP_SYM_FULL,
				 CONTEXT->pi, MAXTRACE, NULL,
				 &CONTEXT->uwcontext, NULL, 0);
	} else {
		_stp_printf("Systemtap probe: %s\n", CONTEXT->probe_point);
	}
%}

/**
 * sfunction sprint_backtrace - Return stack back trace as string (EXPERIMENTAL)
 *
 * Returns a simple (kernel) backtrace. One line per address.
 * Includes the symbol name (or hex address if symbol
 * couldn't be resolved) and module name (if found). Includes the
 * offset from the start of the function if found, otherwise the
 * offset will be added to the module (if found, between
 * brackets). Returns the backtrace as string (each line terminated by
 * a newline character).  Note that the returned stack will be
 * truncated to MAXSTRINGLEN, to print fuller and richer stacks use
 * print_backtrace(). Equivalent to sprint_stack(backtrace()),
 * but more efficient (no need to translate between hex strings and
 * final backtrace string).
 */
function sprint_backtrace:string () %{ /* pure */
	if (CONTEXT->regs && ! (CONTEXT->regflags & _STP_REGS_USER_FLAG))
		_stp_stack_sprint (THIS->__retvalue, MAXSTRINGLEN,
				   _STP_SYM_SIMPLE, CONTEXT->regs,
				   CONTEXT->pi, MAXTRACE, NULL,
				   &CONTEXT->uwcontext, NULL, 0);
	else
		strlcpy (THIS->__retvalue, "", MAXSTRINGLEN);
%}

/**
 * sfunction backtrace - Hex backtrace of current stack
 * 
 * Description: This function returns a string of hex addresses 
 * that are a backtrace of the stack. Output may be truncated as 
 * as per maximum string length (MAXSTRINGLEN).
 */
function backtrace:string () %{ /* pure */
	if (CONTEXT->regs && ! (CONTEXT->regflags & _STP_REGS_USER_FLAG))
		_stp_stack_sprint (THIS->__retvalue, MAXSTRINGLEN,
				   _STP_SYM_NONE, CONTEXT->regs,
				   CONTEXT->pi, MAXTRACE, NULL,
				   &CONTEXT->uwcontext, NULL, 0);
	else 
		strlcpy (THIS->__retvalue, "", MAXSTRINGLEN);
%}

%( systemtap_v <= "1.6" %?
/**
 *  sfunction task_backtrace - Hex backtrace of an arbitrary task
 *  @task: pointer to task_struct
 *
 *  Description: This function returns a string of hex addresses
 *  that are a backtrace of the stack of a particular task
 *  Output may be truncated as per maximum string length.
 *  Deprecated in SystemTap 1.6.
 */
function task_backtrace:string (task:long) %{ /* pure */
	 _stp_stack_snprint_tsk(THIS->__retvalue, MAXSTRINGLEN,
				(struct task_struct *)(unsigned long)THIS->task,
				_STP_SYM_NONE, MAXTRACE);
%}
%)

/**
 *  sfunction caller - Return name and address of calling function
 *
 *  Description: This function returns the address and name of the 
 *  calling function. This is equivalent to calling:
 *  sprintf("%s 0x%x", symname(caller_addr(), caller_addr()))
 *  Works only for return probes at this time.
 */
function caller:string() {
	return sprintf("%s 0x%x", symname(caller_addr()), caller_addr());
}

/**
 *  sfunction caller_addr - Return caller address
 *
 *  Description: This function returns the address of the calling function. 
 *  Works only for return probes at this time.
 */
function caller_addr:long () %{ /* pure */
        if (CONTEXT->pi)
		THIS->__retvalue = (int64_t)(long)_stp_ret_addr_r(CONTEXT->pi);
        else
		THIS->__retvalue = 0;
%}