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Filename : context-caller.stp
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// context-caller tapset
//
// 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>
// Provides caller and caller_addr function for context for kernel and user
// space.
// </tapsetdescription>

%{
/* caller_addr() might be user caller, so needs at least uprobes structs. */
#include "linux/uprobes-inc.h"
%}

/**
 *  sfunction callers - Return first n elements of kernel stack backtrace
 *  
 *  @n: number of levels to descend in the stack (not counting the top
 *  level). If n is -1, print the entire stack.
 *
 *  Description: This function returns a string of the first n hex
 *  addresses from the backtrace of the kernel stack. Output may be
 *  truncated as per maximum string length (MAXSTRINGLEN).
 */
function callers:string (n:long) {
         str = ""; l = 0
         for (i = 0; i <= n || n == -1; i++) {
             foo = i > 0 ? " " : ""
             try {
                 foo .= sprintf("0x%x", stack(i))
             } catch { /* assume we've hit the end of the stack */
                 if (n == -1) break
                 @__context_unwind_error(n)
             }
             // ensure string cuts off cleanly at MAXSTRINGLEN:
             l += strlen(foo); if (l > @MAXSTRINGLEN) break    
             str .= foo
         }
         return str
}

/**
 *  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())
 */
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. 
 */
function caller_addr:long () { return stack(1) }

/* Undocumented function - used in support of .callee[s] probes.
 * Verifies that the current function's caller matches the given addr,
 * accounting for relocation. Used in the constructor of
 * dwarf_derived_probe constructor in tapsets.cxx.
 */
function _caller_match:long (user_mode:long, level:long,
                             module:string, section:string, addr:long) %{
   /* pure */ /* myproc-unprivileged */
   /* pragma:unwind */ /* pragma:uprobes */ /* pragma:vma */
   /* unmodified-fnargs */
   #ifdef STAP_CALLEE_MATCHALL /* Set using -D to have .callee probes fire
                                  regardless of caller */
      STAP_RETVALUE = 1;
   #else
      STAP_RETVALUE = STAP_ARG_user_mode
       ? _stp_stack_user_get(CONTEXT, STAP_ARG_level) ==
            _stp_umodule_relocate(STAP_ARG_module,
                                  STAP_ARG_addr,
                                  current)
       : _stp_stack_kernel_get(CONTEXT, STAP_ARG_level) ==
            _stp_kmodule_relocate(STAP_ARG_module,
                                  STAP_ARG_section,
                                  STAP_ARG_addr);
   #endif
%}