etext (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 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 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 program 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); }

SEE ALSO

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

Information

Source
Linux kernel
OS/version
GNU
Source updated
September 15, 2017
Page created
February 9, 2018
Page generated
December 2, 2018