Developers of Fortran code on NeXTStep (all architectures) have to watch out for the following problem when writing programs with large, statically allocated (i.e. non-stack based) data structures (common blocks, saved arrays).
Due to the way the native loader (/bin/ld) lays out
data structures in virtual memory, it is very easy to create an
executable wherein the __DATA segment overlaps (has addresses in
common) with the UNIX STACK segment.
This leads to all sorts of trouble, from the executable simply not
executing, to bus errors.
The NeXTStep command line tool ebadexec points to
the problem as follows:
% /bin/ebadexec a.out
/bin/ebadexec: __LINKEDIT segment (truncated address = 0x3de000
rounded size = 0x2a000) of executable file: a.out overlaps with UNIX
STACK segment (truncated address = 0x400000 rounded size =
0x3c00000) of executable file: a.out
(In the above case, it is the __LINKEDIT segment that overlaps the
stack segment.)
This can be cured by assigning the __DATA segment
(virtual) addresses beyond the stack segment.
A conservative
estimate for this is from address 6000000 (hexadecimal) onwards--this
has always worked for me [Toon Moene]:
% g77 -segaddr __DATA 6000000 test.f
% ebadexec a.out
ebadexec: file: a.out appears to be executable
%
Browsing through gcc/gcc/f/Makefile.in,
you will find that the f771 program itself also has to be
linked with these flags--it has large statically allocated
data structures.
(Version 0.5.18 reduces this somewhat, but probably
not enough.)
(The above item was contributed by Toon Moene (toon@moene.indiv.nluug.nl).)