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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 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

STANDARDS         top


HISTORY         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

           $ ./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 */

           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)

Linux man-pages (unreleased)   2024-05-02                         end(3)

Pages that refer to this page: brk(2)