Commit 4517a382 authored by Tamar Christina's avatar Tamar Christina Committed by Marge Bot

document how build system find toolchains on Windows

parent f065b6b0
......@@ -507,6 +507,7 @@ AC_DEFUN([GET_ARM_ISA],
# FP_SETTINGS
# ----------------------------------
# Set the variables used in the settings file
# See Note [tooldir: How GHC finds mingw on Windows]
AC_DEFUN([FP_SETTINGS],
[
if test "$windows" = YES -a "$EnableDistroToolchain" = "NO"
......
......@@ -34,16 +34,6 @@ import System.FilePath
import System.Directory (doesDirectoryExist)
#endif
#if defined(mingw32_HOST_OS)
# if defined(i386_HOST_ARCH)
# define WINDOWS_CCONV stdcall
# elif defined(x86_64_HOST_ARCH)
# define WINDOWS_CCONV ccall
# else
# error Unknown mingw32 arch
# endif
#endif
{-
Note [topdir: How GHC finds its files]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......@@ -70,10 +60,83 @@ Note [tooldir: How GHC finds mingw on Windows]
GHC has some custom logic on Windows for finding the mingw
toolchain and perl. Depending on whether GHC is built
with the make build system or Hadrian, and on whether we're
running a bindist, we might find the mingw toolchain and perl
running a bindist, we might find the mingw toolchain
either under $topdir/../{mingw, perl}/ or
$topdir/../../{mingw, perl}/.
This story is long and with lots of twist and turns.. But lets talk about how
the build system finds and wires through the toolchain information.
1) It all starts in configure.ac which has two modes it operates on:
a) The default is where `EnableDistroToolchain` is false. This indicates
that we want to use the in-tree bundled toolchains. In this mode we will
download and unpack some custom toolchains into the `inplace/mingw` folder
and everything is pointed to that folder.
b) The second path is when `EnableDistroToolchain` is true. This makes the
toolchain behave a lot like Linux, in that the environment is queried for
information on the tools we require.
From configure.ac we export the standard variables to set the paths to the
tools for the build system to use.
2) After we have the path to the tools we have to generate the right paths to
store in the settings file for ghc to use. This is done in aclocal.m4.
Again we have two modes of operation:
a) If not `EnableDistroToolchain` the paths are rewritten to paths using a
variable `$tooldir` as we need an absolute path. $tooldir is filled in by
the `expandToolDir` function in this module at GHC startup.
b) When `EnableDistroToolchain` then instead of filling in a absolute path
we fill in just the program name. The assumption here is that at runtime
the environment GHC is operating on will be the same as the one configure
was run in. This means we expect `gcc, ld, as` etc to be on the PATH.
From `aclocal.m4` we export a couple of variables starting with `Settings`
which will be used to generate the settings file.
3) The next step is to generate the settings file, this is where things diverge
based on the build system. Both Make and Hadrian handle this differently:
make)
Make deals with this rather simply. As an output of configure.ac
`config.mk.in` is processed and `config.mk` generated which has the values we
set in `aclocal.m4`. This allows the rest of the build system to have access
to these and other values determined by configure.
Based on this file, `includes/ghc.mk` when ran will produce the settings file
by echoing the values into a the final file. Coincidentally this is also
where `ghcplatform.h` and `ghcversion.h` generated which contains information
about the build platform and sets CPP for use by the entire build.
hadrian)
For hadrian the file `cfg/system.config.in` is preprocessed by configure and
the output written to `system.config`. This serves the same purpose as
`config.mk` but it rewrites the values that were exported. As an example
`SettingsCCompilerCommand` is rewritten to `settings-c-compiler-command`.
Next up is `src/Oracles/Settings.hs` which makes from some Haskell ADT to
the settings `keys` in the `system.config`. As an example,
`settings-c-compiler-command` is mapped to
`SettingsFileSetting_CCompilerCommand`.
The last part of this is the `generateSettings` in `src/Rules/Generate.hs`
which produces the desired settings file out of Hadrian. This is the
equivalent to `includes/ghc.mk`.
--
So why do we have these? On Windows there's no such thing as a platform compiler
and as such we need to provide GCC and binutils. The easiest way is to bundle
these with the compiler and wire them up. This gives you a relocatable
binball. This works fine for most users. However mingw-w64 have a different
requirement. They require all packages in the repo to be compiled using the
same version of the compiler. So it means when they are rebuilding the world to
add support for GCC X, they expect all packages to have been compiled with GCC X
which is a problem since we ship an older GCC version.
GHC is a package in mingw-w64 because there are Haskell packages in the
repository which of course requires a Haskell compiler. To help them we
provide the override which allows GHC to instead of using an inplace compiler to
play nice with the system compiler instead.
-}
-- | Expand occurrences of the @$tooldir@ interpolation in a string
......@@ -113,7 +176,7 @@ tryFindTopDir Nothing
Nothing -> getBaseDir
-- See Note [tooldir: How GHC finds mingw and perl on Windows]
-- See Note [tooldir: How GHC finds mingw on Windows]
-- Returns @Nothing@ when not on Windows.
-- When called on Windows, it either throws an error when the
-- tooldir can't be located, or returns @Just tooldirpath@.
......
......@@ -435,6 +435,7 @@ set_up_tarballs() {
fi
}
# See Note [tooldir: How GHC finds mingw on Windows]
if test "$HostOS" = "mingw32" -a "$EnableDistroToolchain" = "NO"
then
test -d inplace || mkdir inplace
......@@ -455,6 +456,7 @@ fi
# We don't want to bundle a MinGW-w64 toolchain
# So we have to find these individual tools.
# See Note [tooldir: How GHC finds mingw on Windows]
if test "$EnableDistroToolchain" = "YES"
then
# Ideally should use AC_CHECK_TARGET_TOOL but our triples
......
......@@ -129,6 +129,7 @@ conf-merge-objects-args-stage3 = @SettingsMergeObjectsFlags@
# We are in the process of moving the settings file from being entirely
# generated by configure, to generated being by the build system. Many of these
# might become redundant.
# See Note [tooldir: How GHC finds mingw on Windows]
gcc-extra-via-c-opts = @GccExtraViaCOpts@
ld-has-no-compact-unwind = @LdHasNoCompactUnwind@
......
......@@ -184,6 +184,7 @@ settingList key = fmap words $ lookupValueOrError configFile $ case key of
-- | Look up the value of a 'SettingList' in @cfg/system.config@, tracking the
-- result.
-- See Note [tooldir: How GHC finds mingw on Windows]
settingsFileSetting :: SettingsFileSetting -> Action String
settingsFileSetting key = lookupValueOrError configFile $ case key of
SettingsFileSetting_CCompilerCommand -> "settings-c-compiler-command"
......
......@@ -283,6 +283,7 @@ generateGhcPlatformH = do
, "#endif /* __GHCPLATFORM_H__ */"
]
-- See Note [tooldir: How GHC finds mingw on Windows]
generateSettings :: Expr String
generateSettings = do
ctx <- getContext
......
......@@ -207,6 +207,7 @@ $(eval $(call includesHeaderPlatform,1))
# These settings are read by GHC at runtime, so as to not cause spurious
# rebuilds.
# See Note [tooldir: How GHC finds mingw on Windows]
includes_SETTINGS = includes/dist/build/settings
......
......@@ -475,6 +475,7 @@ endif
# We are in the process of moving the settings file from being entirely
# generated by configure, to generated being by the build system. Many of these
# might become redundant.
# See Note [tooldir: How GHC finds mingw on Windows]
GccExtraViaCOpts = @GccExtraViaCOpts@
LdHasFilelist = @LdHasFilelist@
......
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