edata(3) — Linux manual page


END(3)                    Linux Programmer's Manual                   END(3)

NAME         top

       etext, edata, end - end of program segments

SYNOPSIS         top

       extern etext;
       extern edata;
       extern end;

DESCRIPTION         top

       The addresses of these symbols indicate the end of various program

       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

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

CONFORMING TO         top

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

NOTES         top

       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.

EXAMPLES         top

       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 */

       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);


SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

GNU                              2020-06-09                           END(3)