Better hints when RTS options not available (Trac #9579)

This patch provides user with a better hint when most RTS options
are not available (not compiled with `-rtsopts`).

A new field "rtsOptsEnabled" is added into RtsFlags.MiscFlags to
tell the availablity of RTS options.

Some concerns:
* Unlike other flag fields in "libraries/base/GHC/RTS/Flags.hsc",
  "RtsOptsEnabled" is defined in "includes/RtsAPI.h" and lacks
  constant macros. Therefore In "GHC.RTS", "RtsOptsEnabled" simply
  derives Enum instance and reads as of type "CInt".

* There are other ways to change RTS options (e.g. `-with-rtsopts`),
  but it might be too verbose to mention.

Test Plan: validate

Reviewers: austin, hvr, thomie, simonmar

Reviewed By: thomie

Subscribers: thomie, rwbarton

Differential Revision: https://phabricator.haskell.org/D767

GHC Trac Issues: #9579

2 files changed, 18 insertions, 6 deletions

diff --git a/rts/hooks/OutOfHeap.c b/rts/hooks/OutOfHeap.c
index 501bccddb7..bb8752846f 100644
--- a/rts/hooks/OutOfHeap.c
+++ b/rts/hooks/OutOfHeap.c
@@ -7,19 +7,23 @@
 #include "PosixSource.h"
 #include "Rts.h"
 #include "Hooks.h"
+#include "RtsFlags.h"
 #include <stdio.h>
 
 void
 OutOfHeapHook (W_ request_size, W_ heap_size) /* both sizes in bytes */
 {
-  /*    fprintf(stderr, "Heap exhausted;\nwhile trying to allocate %lu bytes in a %lu-byte heap;\nuse `+RTS -H<size>' to increase the total heap size.\n", */
-
   (void)request_size;   /* keep gcc -Wall happy */
   if (heap_size > 0) {
-      errorBelch("Heap exhausted;\nCurrent maximum heap size is %" FMT_Word " bytes (%" FMT_Word " MB);\nuse `+RTS -M<size>' to increase it.",
-          heap_size, heap_size / (1024*1024));
+      errorBelch("Heap exhausted;\n"
+                 "Current maximum heap size is %" FMT_Word
+                 " bytes (%" FMT_Word " MB);\n"
+                 "%s `+RTS -M<size>' to increase it.",
+                 heap_size, heap_size / (1024*1024),
+                 ((rtsConfig.rts_opts_enabled == RtsOptsAll)
+                  ? "use"
+                  : "relink with -rtsopts and use"));
   } else {
       errorBelch("out of memory");
   }
 }
-
diff --git a/rts/hooks/StackOverflow.c b/rts/hooks/StackOverflow.c
index 1095b1b81d..1ae8603eec 100644
--- a/rts/hooks/StackOverflow.c
+++ b/rts/hooks/StackOverflow.c
@@ -7,11 +7,19 @@
 #include "PosixSource.h"
 #include "Rts.h"
 #include "Hooks.h"
+#include "RtsFlags.h"
 
 #include <stdio.h>
 
 void
 StackOverflowHook (W_ stack_size)    /* in bytes */
 {
-    fprintf(stderr, "Stack space overflow: current size %" FMT_Word " bytes.\nUse `+RTS -Ksize -RTS' to increase it.\n", stack_size);
+    fprintf(stderr,
+            "Stack space overflow: current size %" FMT_Word " bytes.\n"
+            "%s `+RTS -Ksize -RTS' to increase it.\n",
+            stack_size,
+            ((rtsConfig.rts_opts_enabled == RtsOptsAll)
+             ? "Use"
+             : "Relink with -rtsopts and use")
+            );
 }