etext, edata, end - end of program segments
The addresses of these symbols indicate the end of various program segments:
- This is the first address past the end of the text segment (the program
- This is the first address past the end of the initialized data
- This 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
On some systems the names of these symbols are preceded by underscores, thus:
, 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
(perhaps at the start of the following page). However, the
break will change as memory is allocated via brk
(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:
First address past:
program text (etext) 0x8048568
initialized data (edata) 0x804a01c
uninitialized data (end) 0x804a024
extern char etext, edata, end; /* The symbols must have some type,
or "gcc -Wall" complains */
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);