csu/gmon-start.c

   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 }