GNU Info

(g77-300.info)Stack Overflow

---

Next: Nothing Happens Prev: NeXTStep Problems Up: But-bugs

---

Enter node , (file) or (file)node

Stack Overflow
--------------

   `g77' code might fail at runtime (probably with a "segmentation
violation") due to overflowing the stack.  This happens most often on
systems with an environment that provides substantially more heap space
(for use when arbitrarily allocating and freeing memory) than stack
space.

   Often this can be cured by increasing or removing your shell's limit
on stack usage, typically using `limit stacksize' (in `csh' and
derivatives) or `ulimit -s' (in `sh' and derivatives).

   Increasing the allowed stack size might, however, require changing
some operating system or system configuration parameters.

   You might be able to work around the problem by compiling with the
`-fno-automatic' option to reduce stack usage, probably at the expense
of speed.

   `g77', on most machines, puts many variables and arrays on the stack
where possible, and can be configured (by changing
`FFECOM_sizeMAXSTACKITEM' in `gcc/gcc/f/com.c') to force smaller-sized
entities into static storage (saving on stack space) or permit
larger-sized entities to be put on the stack (which can improve
run-time performance, as it presents more opportunities for the GBE to
optimize the generated code).

   _Note:_ Putting more variables and arrays on the stack might cause
problems due to system-dependent limits on stack size.  Also, the value
of `FFECOM_sizeMAXSTACKITEM' has no effect on automatic variables and
arrays.  Note: But-bugs, for more information.  _Note:_ While
`libg2c' places a limit on the range of Fortran file-unit numbers, the
underlying library and operating system might impose different kinds of
limits.  For example, some systems limit the number of files
simultaneously open by a running program.  Information on how to
increase these limits should be found in your system's documentation.

   However, if your program uses large automatic arrays (for example,
has declarations like `REAL A(N)' where `A' is a local array and `N' is
a dummy or `COMMON' variable that can have a large value), neither use
of `-fno-automatic', nor changing the cut-off point for `g77' for using
the stack, will solve the problem by changing the placement of these
large arrays, as they are _necessarily_ automatic.

   `g77' currently provides no means to specify that automatic arrays
are to be allocated on the heap instead of the stack.  So, other than
increasing the stack size, your best bet is to change your source code
to avoid large automatic arrays.  Methods for doing this currently are
outside the scope of this document.

   (_Note:_ If your system puts stack and heap space in the same memory
area, such that they are effectively combined, then a stack overflow
probably indicates a program that is either simply too large for the
system, or buggy.)