|Version 6 (modified by 9 years ago) (diff),|
Platforms, scripts, and file names
GHC is designed both to be built, and to run, on both Unix and Windows. This flexibility gives rise to a good deal of brain-bending detail, which we have tried to collect in this chapter.
Windows platforms: Cygwin, MSYS, and MinGW
The build system is built around Unix-y makefiles. Because it's not native, the Windows situation for building GHC is particularly confusing. This section tries to clarify, and to establish terminology.
MinGW (Minimalist GNU for Windows)
is a collection of header
files and import libraries that allow one to use
gcc and produce
native Win32 programs that do not rely on any third-party DLLs. The
current set of tools include GNU Compiler Collection (
gcc), GNU Binary
Utilities (Binutils), GNU debugger (Gdb), GNU make, and assorted
GHC requires both the MinGW "core system" (a C compiler + other essential stuff) and the g++ system (required by libffi) to be installed.
The down-side of MinGW is that the MinGW libraries do not support anything like the full Posix interface.
Cygwin and MSYS
You can't use the MinGW to build GHC, because MinGW doesn't have a shell,
or the standard Unix commands such as
ls, nor build-system stuff such as
For that, there are two choices: Cygwin
- Cygwin comes with compilation tools (
ldand so on), which compile code that has access to all of Posix. The price is that the executables must be dynamically linked with the Cygwin DLL, so that you cannot run a Cywin-compiled program on a machine that doesn't have Cygwin. Worse, Cygwin is a moving target. The name of the main DLL,
cygwin1.dlldoes not change, but the implementation certainly does. Even the interfaces to functions it exports seem to change occasionally.
- MSYS is a fork of the Cygwin tree, so they
are fundamentally similar. However, MSYS is by design much smaller and simpler.
Access to the file system goes
through fewer layers, so MSYS is quite a bit faster too.
Furthermore, MSYS provides no compilation tools; it relies instead on the MinGW tools. These compile binaries that run with no DLL support, on any Win32 system. However, MSYS does come with all the make-system tools, such as
sshetc. To get these, you have to download the MsysDTK (Developer Tool Kit) package, as well as the base MSYS package.
MSYS does have a DLL, but it's only used by MSYS commands (
sshand so on), not by programs compiled under MSYS.
We want GHC to compile programs that work on any Win32 system. Hence:
- GHC does invoke a C compiler, assembler, linker and so on, but we ensure that it only invokes the MinGW tools, not the Cygwin ones. That means that the programs GHC compiles will work on any system, but it also means that the programs GHC compiles do not have access to all of Posix. In particular, they cannot import the (Haskell) Posix library; they have to do their input output using standard Haskell I/O libraries, or native Win32 bindings. We will call a GHC that targets MinGW in this way GHC-mingw.
- To make the GHC distribution self-contained, the GHC distribution includes the MinGW
ld, and a bunch of input/output libraries.
So GHC targets MinGW, not Cygwin. It is in principle possible to build a version of GHC, GHC-cygwin, that targets Cygwin instead. The up-side of GHC-cygwin is that Haskell programs compiled by GHC-cygwin can import the (Haskell) Posix library. We do not support GHC-cygwin, however; it is beyond our resources.
While GHC targets MinGW, that says nothing about how GHC is built. We use both MSYS and Cygwin as build environments for GHC; both work fine, though MSYS is rather lighter weight.
In your build tree, the compiler you build uses the
gcc that you specify using the
--with-gcc flag when you run
configure (see below).
The makefiles are careful to use the right gcc, either via the in-place ghc or directly,
to compile any C files, so that we use correct
gcc rather than
whatever one happens to be in your path. However, the makefiles do use whatever
ar happen to be in your path. This is a bit naughty, but (a) they are only
used to glom together .o files into a bigger .o file, or a .a file,
so they don't ever get libraries (which would be bogus; they might be the wrong libraries), and (b)
Cygwin and MinGW use the same .o file format. So its ok.
Cygwin, MSYS, and the underlying Windows file system all understand file paths of form
- MSYS programs understand
/usr/bin, and map Windows's lettered drives as
/c/tmp/fooetc. The exact mount table is given in the doc subdirectory of the MSYS distribution.
When it invokes a command, the MSYS shell sees whether the invoked binary lives in the MSYS
/bindirectory. If so, it just invokes it. If not, it assumes the program is no an MSYS program, and walks over the command-line arguments changing MSYS paths into native-compatible paths. It does this inside sub-arguments and inside quotes. For example, if you invoke
foogle -B/c/tmp/bazthe MSYS shell will actually call
- Cygwin programs have a more complicated mount table, and map the lettered drives as
The Cygwin shell does no argument processing when invoking non-Cygwin programs.
It turns out that on both Cygwin and MSYS, the
ld has a
limit of 32kbytes on its command line. Especially when using split object
files, the make system can emit calls to
ld with thousands
of files on it. Then you may see something like this:
(cd Graphics/Rendering/OpenGL/GL/QueryUtils_split && /mingw/bin/ld -r -x -o ../QueryUtils.o *.o) /bin/sh: /mingw/bin/ld: Invalid argument
The solution is either to switch off object file splitting (set
NO in your
or to make the module smaller.
Host System vs Target System
In the source code you'll find various ifdefs looking like:
#ifdef mingw32_HOST_OS ...blah blah... #endif
#ifdef mingw32_TARGET_OS ...blah blah... #endif
These macros are set by the configure script (via the file config.h). Which is which? The criterion is this. In the ifdefs in GHC's source code:
- The "host" system is the one on which GHC itself will be run.
- The "target" system is the one for which the program compiled by GHC will be run.
For a stage-2 compiler, in which GHCi is available, the "host" and "target" systems must be the same. So then it doesn't really matter whether you use the HOST_OS or TARGET_OS cpp macros.
Many programs, including GHC itself and hsc2hs, need to find associated binaries and libraries. For installed programs, the strategy depends on the platform. We'll use GHC itself as an example:
- On Unix, the command
ghcis a shell script, generated by Cabal from
ghc/ghc.wrapper, that invokes the real binary, passing "-Bpath" as an argument to tell
ghcwhere to find its supporting files.
- On vanilla Windows, it turns out to be much harder to make reliable script to be run by the
native Windows shell
cmd(e.g. limits on the length of the command line). So instead we invoke the GHC binary directly, with no -B flag. GHC uses the Windows
getExecDirfunction to find where the executable is, and from that figures out where the supporting files are.
(You can find the layout of GHC's supporting files in the section "Layout of installed files" of Section 2 of the GHC user guide.)
Things work differently for in-place execution, where you want to
execute a program that has just been built in a build tree. The difference is that the
layout of the supporting files is different.
In this case, whether on Windows or Unix, we always use a shell script. This works OK
on Windows because the script is executed by MSYS or Cygwin, which don't have the
shortcomings of the native Windows