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:0); printf(" program text (etext) %10p0, &etext); printf(" initialized data (edata) %10p0, &edata); printf(" uninitialized data (end) %10p0, &end);


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

COLOPHON This page is part of release 3.22 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

GNU 2008-07-17 END(3)