1  /* Code to enable profiling at program startup.
       2     Copyright (C) 1995-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     In addition to the permissions in the GNU Lesser General Public
      11     License, the Free Software Foundation gives you unlimited
      12     permission to link the compiled version of this file with other
      13     programs, and to distribute those programs without any restriction
      14     coming from the use of this file.  (The GNU Lesser General Public
      15     License restrictions do apply in other respects; for example, they
      16     cover modification of the file, and distribution when not linked
      17     into another program.)
      18  
      19     Note that people who make modified versions of this file are not
      20     obligated to grant this special exception for their modified
      21     versions; it is their choice whether to do so.  The GNU Lesser
      22     General Public License gives permission to release a modified
      23     version without this exception; this exception also makes it
      24     possible to release a modified version which carries forward this
      25     exception.
      26  
      27     The GNU C Library is distributed in the hope that it will be useful,
      28     but WITHOUT ANY WARRANTY; without even the implied warranty of
      29     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      30     Lesser General Public License for more details.
      31  
      32     You should have received a copy of the GNU Lesser General Public
      33     License along with the GNU C Library; if not, see
      34     <https://www.gnu.org/licenses/>.  */
      35  
      36  #include <sys/types.h>
      37  #include <sys/gmon.h>
      38  #include <stdlib.h>
      39  #include <unistd.h>
      40  #include <elf-initfini.h>
      41  
      42  /* Use __executable_start as the lowest address to keep profiling records
      43     if it provided by the linker.  */
      44  extern const char __executable_start[] __attribute__ ((visibility ("hidden")));
      45  
      46  extern char etext[];
      47  
      48  #if !ELF_INITFINI
      49  /* Instead of defining __gmon_start__ globally in gcrt1.o, we make it
      50     static and just put a pointer to it into the .preinit_array
      51     section.  */
      52  # define GMON_START_ARRAY_SECTION ".preinit_array"
      53  #endif
      54  
      55  #ifdef GMON_START_ARRAY_SECTION
      56  static void __gmon_start__ (void);
      57  static void (*const gmon_start_initializer) (void)
      58    __attribute__ ((used, section (GMON_START_ARRAY_SECTION))) = &__gmon_start__;
      59  static
      60  #else
      61  /* We cannot use the normal constructor mechanism to call
      62     __gmon_start__ because gcrt1.o appears before crtbegin.o in the link.
      63     Instead crti.o calls it specially.  */
      64  extern void __gmon_start__ (void);
      65  #endif
      66  
      67  void
      68  __gmon_start__ (void)
      69  {
      70    /* Protect from being called more than once.  Since crti.o is linked
      71       into every shared library, each of their init functions will call us.  */
      72    static int called;
      73  
      74    if (called)
      75      return;
      76  
      77    called = 1;
      78  
      79    /* Start keeping profiling records.  */
      80    __monstartup ((u_long) &__executable_start, (u_long) &etext);
      81  
      82    /* Call _mcleanup before exiting; it will write out gmon.out from the
      83       collected data.  */
      84    atexit (&_mcleanup);
      85  }