Minix Man Pages

home | help
x minix x
x minixx
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 seg-
       ments:

       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  pro-
       gram 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 5.05 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/.

GNU                               2019-03-06                            END(3)
NAME | SYNOPSIS | DESCRIPTION | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON