END(3)                              Linux Programmer's Manual                              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  stan‐
       dardized; 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  allo‐
       cated  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 3.74 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 http://www.kernel.org/doc/man-pages/.



GNU                                         2008-07-17                                     END(3)