10. Known pitfalls in building Glasgow Haskell
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## 10. Known pitfalls in building Glasgow Haskell

WARNINGS about pitfalls and known “problems”:

1. One difficulty that comes up from time to time is running out of space in `TMPDIR`. (It is impossible for the configuration stuff to compensate for the vagaries of different sysadmin approaches to temp space.) The quickest way around it is setenv TMPDIR /usr/tmp or even setenv TMPDIR . (or the equivalent incantation with your shell of choice). The best way around it is to say

       export TMPDIR=<dir>

   in your `build.mk` file. Then GHC and the other tools will use the appropriate directory in all cases.

2. In compiling some support-code bits, e.g., in `ghc/rts/gmp` and even in `ghc/lib`, you may get a few C-compiler warnings. We think these are OK.

3. When compiling via C, you'll sometimes get “warning: assignment from incompatible pointer type” out of GCC. Harmless.

4. Similarly, archiving warning messages like the following are not a problem:

       ar: filename GlaIOMonad__1_2s.o truncated to GlaIOMonad_
       ar: filename GlaIOMonad__2_2s.o truncated to GlaIOMonad_
       ...

5. In compiling the compiler proper (in `compiler/`), you may get an “Out of heap space” error message. These can vary with the vagaries of different systems, it seems. The solution is simple:

   - If you're compiling with GHC 4.00 or later, then the maximum heap size must have been reached. This is somewhat unlikely, since the maximum is set to 64M by default. Anyway, you can raise it with the `-optCrts-M<size>` flag (add this flag to `<module>_HC_OPTS` make variable in the appropriate `Makefile`).

   - For GHC < 4.00, add a suitable `-H` flag to the `Makefile`, as above.

   and try again: make. (see Section 7.6, “Pattern rules and options” for information about `<module>_HC_OPTS`.) Alternatively, just cut to the chase:

       $ cd ghc/compiler
       $ make EXTRA_HC_OPTS=-optCrts-M128M

6. If you try to compile some Haskell, and you get errors from GCC about lots of things from `/usr/include/math.h`, then your GCC was mis-installed. fixincludes wasn't run when it should've been. As fixincludes is now automagically run as part of GCC installation, this bug also suggests that you have an old GCC.

7. You may need to re-ranlib your libraries (on Sun4s).

       $ cd $(libdir)/ghc-x.xx/sparc-sun-sunos4
       $ foreach i ( `find . -name '*.a' -print` ) # or other-shell equiv...
       ?    ranlib $i
       ?    # or, on some machines: ar s $i
       ? end

   We'd be interested to know if this is still necessary.

8. GHC's sources go through cpp before being compiled, and cpp varies a bit from one Unix to another. One particular gotcha is macro calls like this:

       SLIT("Hello, world")

   Some cpps treat the comma inside the string as separating two macro arguments, so you get

       :731: macro `SLIT' used with too many (2) args

   Alas, cpp doesn't tell you the offending file! Workaround: don't put weird things in string args to cpp macros.

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