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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); }