Change the way module initialisation is done (#3252, #4417)

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.

1 files changed, 6 insertions, 10 deletions

diff --git a/rts/RtsMain.c b/rts/RtsMain.c
index b6cf546aea..0ed6df494c 100644
--- a/rts/RtsMain.c
+++ b/rts/RtsMain.c
@@ -28,13 +28,10 @@
 # include <windows.h>
 #endif
 
-extern void __stginit_ZCMain(void);
-
 /* Annoying global vars for passing parameters to real_main() below
  * This is to get around problem with Windows SEH, see hs_main(). */
 static int progargc;
 static char **progargv;
-static void (*progmain_init)(void);   /* This will be __stginit_ZCMain */
 static StgClosure *progmain_closure;  /* This will be ZCMain_main_closure */
 
 /* Hack: we assume that we're building a batch-mode system unless 
@@ -47,7 +44,7 @@ static void real_main(void)
     SchedulerStatus status;
     /* all GranSim/GUM init is done in startupHaskell; sets IAmMainThread! */
 
-    startupHaskell(progargc,progargv,progmain_init);
+    startupHaskell(progargc,progargv,NULL);
 
     /* kick off the computation by creating the main thread with a pointer
        to mainIO_closure representing the computation of the overall program;
@@ -95,18 +92,17 @@ static void real_main(void)
  * This gets called from a tiny main function which gets linked into each
  * compiled Haskell program that uses a Haskell main function.
  *
- * We expect the caller to pass __stginit_ZCMain for main_init and
- * ZCMain_main_closure for main_closure. The reason we cannot refer to
- * these symbols directly is because we're inside the rts and we do not know
- * for sure that we'll be using a Haskell main function.
+ * We expect the caller to pass ZCMain_main_closure for
+ * main_closure. The reason we cannot refer to this symbol directly
+ * is because we're inside the rts and we do not know for sure that
+ * we'll be using a Haskell main function.
  */
-int hs_main(int argc, char *argv[], void (*main_init)(void), StgClosure *main_closure)
+int hs_main(int argc, char *argv[], StgClosure *main_closure)
 {
     /* We do this dance with argc and argv as otherwise the SEH exception
        stuff (the BEGIN/END CATCH below) on Windows gets confused */
     progargc = argc;
     progargv = argv;
-    progmain_init    = main_init;
     progmain_closure = main_closure;
 
 #if defined(mingw32_HOST_OS)