end(3) Library Functions 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).
STANDARDS
None.
HISTORY
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 pro-
grams 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.
EXAMPLES
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(void)
{
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);
}
SEE ALSO
objdump(1), readelf(1), sbrk(2), elf(5)
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