wiki:Building/FAQ

Version 3 (modified by tphyahoo, 7 years ago) (diff)

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Frequently asked questions about building GHC

This page collects questions and advice about building GHC from source. It is particularly prone to going out of date. Please help keep it relevant and accurate. At the moment it's fairly un-structured; please feel free to add structure if that'd make it easier to follow.

Platform-specific guidance belongs under one of the platform-specific help pages linked from the Building guide contents page.

Space in TMPDIR

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.

Warning "warning: assignment from incompatible pointer type"

You may occasionally see a warning from the C compiler when compiling some Haskell code, eg. "warning: assignment from incompatible pointer type". These are usually harmless, but it's a good idea to report it on the mailing list so that we can fix it.

Warning "ar: filename GlaIOMonad__1_2s.o truncated to GlaIOMonad_"

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_
...

GCC 4 issues

It has been observed on Gentoo systems that GCC 4 may fail, complaining about there being no -nopie option. You can either use GCC 3, re-emerge ghc or just edit your /usr/bin/ghc script to remove the -nopie flag (the latter is by far the quickest and is perfectly safe).

Cpp variations

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.

Cabal/Distribution/Compat/FilePath?.hs: No such file or directory

You may see this:

Distribution/Compat/FilePath.hs:2: 
  error: Cabal/Distribution/Compat/FilePath.hs: No such file or directory
make[1]: *** [depend] Error 1
make: *** [stage1] Error 1

Possible Solution:: Be sure you have run sh darcs-all get to get all necessary packages. Don't forget to run autoreconf again after you pull in new packages.

xargs: /usr/bin/ar: terminated by signal 11

You may see this when compiling libraries:

(echo Control/Concurrent_stub.o System/CPUTime_hsc.o System/Time_hsc.o ;
/usr/bin/find Control/Applicative_split Control/Arrow_split
Control/Concurrent_split Control/Concurrent/Chan_split 
   ...long mess...
Text/PrettyPrint/HughesPJ_split Text/Printf_split Text/Read_split
Text/Read/Lex_split Text/Show_split Text/Show/Functions_split -name '*.o'
-print) | xargs /usr/bin/ar q libHSbase.a
/usr/bin/ar: creating libHSbase.a
xargs: /usr/bin/ar: terminated by signal 11
make[2]: *** [libHSbase.a] Error 125
make[2]: *** Deleting file `libHSbase.a'
make[1]: *** [all] Error 1

What is happening is that the ghc build system is linking thousands and thousands of tiny .o files into libHSbase.a. GNU ar isn't optimised for this use-case and it takes far more memory than it really needs to. So what happens is that ar takes >500Mb of memory and your virtual machine / virtual server probably isn't configured with that much memory and so the linux kernel OOM killer terminates the ar process.

To make this worse, since there are so many .o files, it takes several invocations of ar to link them all. On each invocation ar is building the symbol index (-q is ignored) and this is what takes the most time and memory. It's a good deal quicker to use a custom program (100 lines of Haskell) to build libHSbase.a and then use ranlib just once to build the symbol index.

[Duncan Coutts] I submitted a patch to gnu binutils to make ar take less memory when linking 1000's of files so it now only takes around 100Mb rather than 500Mb when linking libHSbase.a. That patch is included in version 2.17 I think (in other words most systems don't have it yet).

What you can do in the mean time is either configure your virtual machine with more memory or turn off the split-objs feature when you configure ghc. Just add SplitObjs=NO to your mk/build.mk file (which may not exist to start with). (The Gentoo ebuild does this automatically)

Note: The above didn't work for me when I created mk/build.mk with the SplitObjs? directive. But when I made the change to mk/config.mk, by uncommenting a line near the end of the file, it worked.