etext, edata, end — end of program segments
extern etext; extern edata; extern end;
The addresses of these symbols indicate the end of various program segments:
etextThis is the first address past the end of the text segment (the program code).
edataThis is the first address past the end of the initialized data segment.
endThis is the first address past the end of the uninitialized data segment (also known as the BSS segment).
Although these symbols have long been provided on most UNIX systems, they are not standardized; use with caution.
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.
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
#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);
}
This page is part of release 4.07 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/.
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Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |