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, 28 insertions, 40 deletions

diff --git a/rts/Profiling.c b/rts/Profiling.c
index 1d8627c5b1..5648f31e00 100644
--- a/rts/Profiling.c
+++ b/rts/Profiling.c
@@ -34,9 +34,9 @@ Arena *prof_arena;
  * closure_cats
  */
 
-unsigned int CC_ID;
-unsigned int CCS_ID;
-unsigned int HP_ID;
+unsigned int CC_ID  = 1;
+unsigned int CCS_ID = 1;
+unsigned int HP_ID  = 1;
 
 /* figures for the profiling report.
  */
@@ -58,8 +58,8 @@ CostCentreStack *CCCS;
 /* Linked lists to keep track of cc's and ccs's that haven't
  * been declared in the log file yet
  */
-CostCentre *CC_LIST;
-CostCentreStack *CCS_LIST;
+CostCentre      *CC_LIST  = NULL;
+CostCentreStack *CCS_LIST = NULL;
 
 /*
  * Built-in cost centres and cost-centre stacks:
@@ -152,41 +152,10 @@ initProfiling1 (void)
 
   /* for the benefit of allocate()... */
   CCCS = CCS_SYSTEM;
-  
-  /* Initialize counters for IDs */
-  CC_ID  = 1;
-  CCS_ID = 1;
-  HP_ID  = 1;
-  
-  /* Initialize Declaration lists to NULL */
-  CC_LIST  = NULL;
-  CCS_LIST = NULL;
-
-  /* Register all the cost centres / stacks in the program 
-   * CC_MAIN gets link = 0, all others have non-zero link.
-   */
-  REGISTER_CC(CC_MAIN);
-  REGISTER_CC(CC_SYSTEM);
-  REGISTER_CC(CC_GC);
-  REGISTER_CC(CC_OVERHEAD);
-  REGISTER_CC(CC_SUBSUMED);
-  REGISTER_CC(CC_DONT_CARE);
-  REGISTER_CCS(CCS_MAIN);
-  REGISTER_CCS(CCS_SYSTEM);
-  REGISTER_CCS(CCS_GC);
-  REGISTER_CCS(CCS_OVERHEAD);
-  REGISTER_CCS(CCS_SUBSUMED);
-  REGISTER_CCS(CCS_DONT_CARE);
-
-  CCCS = CCS_OVERHEAD;
-
-  /* cost centres are registered by the per-module 
-   * initialisation code now... 
-   */
 }
 
 void
-freeProfiling1 (void)
+freeProfiling (void)
 {
     arenaFree(prof_arena);
 }
@@ -202,17 +171,36 @@ initProfiling2 (void)
    * information into it.  */
   initProfilingLogFile();
 
+  /* Register all the cost centres / stacks in the program
+   * CC_MAIN gets link = 0, all others have non-zero link.
+   */
+  REGISTER_CC(CC_MAIN);
+  REGISTER_CC(CC_SYSTEM);
+  REGISTER_CC(CC_GC);
+  REGISTER_CC(CC_OVERHEAD);
+  REGISTER_CC(CC_SUBSUMED);
+  REGISTER_CC(CC_DONT_CARE);
+
+  REGISTER_CCS(CCS_SYSTEM);
+  REGISTER_CCS(CCS_GC);
+  REGISTER_CCS(CCS_OVERHEAD);
+  REGISTER_CCS(CCS_SUBSUMED);
+  REGISTER_CCS(CCS_DONT_CARE);
+  REGISTER_CCS(CCS_MAIN);
+
   /* find all the "special" cost centre stacks, and make them children
    * of CCS_MAIN.
    */
-  ASSERT(CCS_MAIN->prevStack == 0);
+  ASSERT(CCS_LIST == CCS_MAIN);
+  CCS_LIST = CCS_LIST->prevStack;
+  CCS_MAIN->prevStack = NULL;
   CCS_MAIN->root = CC_MAIN;
   ccsSetSelected(CCS_MAIN);
   DecCCS(CCS_MAIN);
 
-  for (ccs = CCS_LIST; ccs != CCS_MAIN; ) {
+  for (ccs = CCS_LIST; ccs != NULL; ) {
     next = ccs->prevStack;
-    ccs->prevStack = 0;
+    ccs->prevStack = NULL;
     ActualPush_(CCS_MAIN,ccs->cc,ccs);
     ccs->root = ccs->cc;
     ccs = next;