Previously the code generator generated small code fragments labelled with __stginit_M for each module M, and these performed whatever initialisation was necessary for that module and recursively invoked the initialisation functions for imported modules. This appraoch had drawbacks: - FFI users had to call hs_add_root() to ensure the correct initialisation routines were called. This is a non-standard, and ugly, API. - unless we were using -split-objs, the __stginit dependencies would entail linking the whole transitive closure of modules imported, whether they were actually used or not. In an extreme case (#4387, #4417), a module from GHC might be imported for use in Template Haskell or an annotation, and that would force the whole of GHC to be needlessly linked into the final executable. So now instead we do our initialisation with C functions marked with __attribute__((constructor)), which are automatically invoked at program startup time (or DSO load-time). The C initialisers are emitted into the stub.c file. This means that every time we compile with -prof or -hpc, we now get a stub file, but thanks to #3687 that is now invisible to the user. There are some refactorings in the RTS (particularly for HPC) to handle the fact that initialisers now get run earlier than they did before. The __stginit symbols are still generated, and the hs_add_root() function still exists (but does nothing), for backwards compatibility.
The first phase of this tidyup is focussed on the header files, and in particular making sure we are exposinng publicly exactly what we need to, and no more. - Rts.h now includes everything that the RTS exposes publicly, rather than a random subset of it. - Most of the public header files have moved into subdirectories, and many of them have been renamed. But clients should not need to include any of the other headers directly, just #include the main public headers: Rts.h, HsFFI.h, RtsAPI.h. - All the headers needed for via-C compilation have moved into the stg subdirectory, which is self-contained. Most of the headers for the rest of the RTS APIs have moved into the rts subdirectory. - I left MachDeps.h where it is, because it is so widely used in Haskell code. - I left a deprecated stub for RtsFlags.h in place. The flag structures are now exposed by Rts.h. - Various internal APIs are no longer exposed by public header files. - Various bits of dead code and declarations have been removed - More gcc warnings are turned on, and the RTS code is more warning-clean. - More source files #include "PosixSource.h", and hence only use standard POSIX (1003.1c-1995) interfaces. There is a lot more tidying up still to do, this is just the first pass. I also intend to standardise the names for external RTS APIs (e.g use the rts_ prefix consistently), and declare the internal APIs as hidden for shared libraries.
Previously the object code for the C main function lived in the rts lib, however this is a problem when the rts is built as a shared lib. With Windows DLLs it always causes problems while on ELF systems it's a problem when the user decides to use their own C main function rather than a Haskell Main.main. So instead we now put main in it's own tiny little static lib libHSrtsmain.a which we install next to the rts libs. Whenever ghc links a program (without -no-hs-main) then it also links in -lHSrtsmain. For consistency we always do it this way now rather than trying to do it differently for static vs shared libraries.
Really we should be raising an exception in this case, but that's tricky (see comments). At least now we shut down the runtime correctly rather than just exiting.
Adaptated from code from Sigbjorn Finne
In preparation for parallel GC, split up the monolithic GC.c file into smaller parts. Also in this patch (and difficult to separate, unfortunatley): - Don't include Stable.h in Rts.h, instead just include it where necessary. - consistently use STATIC_INLINE in source files, and INLINE_HEADER in header files. STATIC_INLINE is now turned off when DEBUG is on, to make debugging easier. - The GC no longer takes the get_roots function as an argument. We weren't making use of this generalisation.
Most of the other users of the fptools build system have migrated to Cabal, and with the move to darcs we can now flatten the source tree without losing history, so here goes. The main change is that the ghc/ subdir is gone, and most of what it contained is now at the top level. The build system now makes no pretense at being multi-project, it is just the GHC build system. No doubt this will break many things, and there will be a period of instability while we fix the dependencies. A straightforward build should work, but I haven't yet fixed binary/source distributions. Changes to the Building Guide will follow, too.