end(3)

NAME

   etext, edata, end - end of program segments

SYNOPSIS

   extern etext;
   extern edata;
   extern end;

DESCRIPTION

   The  addresses  of  these  symbols  indicate the end of various program
   segments:

   etext  This is the first address past the end of the text segment  (the
          program code).

   edata  This  is  the first address past the end of the initialized data
          segment.

   end    This is the first address past the end of the uninitialized data
          segment (also known as the BSS segment).

CONFORMING TO

   Although  these  symbols  have long been provided on most UNIX systems,
   they are not standardized; use with caution.

NOTES

   The program must explicitly declare these symbols; they are not defined
   in any header file.

   On some systems the names of these symbols are preceded by underscores,
   thus: _etext, _edata, and _end.  These symbols  are  also  defined  for
   programs compiled on Linux.

   At  the start of program execution, the program break will be somewhere
   near &end (perhaps at the start of the following page).   However,  the
   break  will change as memory is allocated via brk(2) or malloc(3).  Use
   sbrk(2) with an argument of zero to  find  the  current  value  of  the
   program break.

EXAMPLE

   When run, the program below produces output such as the following:

       $ ./a.out
       First address past:
           program text (etext)       0x8048568
           initialized data (edata)   0x804a01c
           uninitialized data (end)   0x804a024

   Program source

   #include <stdio.h>
   #include <stdlib.h>

   extern char etext, edata, end; /* The symbols must have some type,
                                      or "gcc -Wall" complains */

   int
   main(int argc, char *argv[])
   {
       printf("First address past:\n");
       printf("    program text (etext)      %10p\n", &etext);
       printf("    initialized data (edata)  %10p\n", &edata);
       printf("    uninitialized data (end)  %10p\n", &end);

       exit(EXIT_SUCCESS);
   }

SEE ALSO

   objdump(1), readelf(1), sbrk(2), elf(5)

COLOPHON

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

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