NAME
end, etext, edata - last locations in program
SYNOPSIS
extern end;
extern etext;
extern edata;
DESCRIPTION
These names refer neither to routines nor to locations with
interesting contents. Instead, their addresses coincide
with the first address above the program text region
(etext), above the initialized data region (edata), or
uninitialized data region (end). The last is the same as
the program break. Values are given to these symbols by the
link editor ld (I) when, and only when, they are referred to
but not defined in the set of programs loaded.
The usage of these symbols is rather specialized, but one
plausible possibility is
extern end;
...
... = brk(&end+...);
(see break (II)). The problem with this is that it ignores
any other subroutines which may want to extend core for
their purposes; these include sbrk (see break (II)), alloc
(III), and also secret subroutines invoked by the profile
(-p) option of cc. Of course it was for the benefit of such
systems that the symbols were invented, and user programs,
unless they are in firm control of their environment, are
wise not to refer to the absolute symbols directly.
One technique sometimes useful is to call sbrk(0), which
returns the value of the current program break, instead of
referring to &end, which yields the program break at the
instant execution started.
These symbols are accessible from assembly language if it is
remembered that they should be prefixed by `_'
SEE ALSO
break (II), alloc (III)
BUGS
1