Add --arbitrary-heap-start description to runtime_control.rst and rts/RtsFlags.c

docs/users_guide/runtime_control.rst

@@ -721,6 +721,18 @@ performance.
     the default small ``-A`` value is suboptimal, as it can be in
     programs that create large amounts of long-lived data.
 
+.. rts-flag:: --arbitrary-heap-start
+
+    :default: disabled
+    :since: 9.4
+
+    .. index::
+       single: arbitrary heap start
+
+    By default heap base offset for the garbage collector is selected above 0x200000000
+    because otherwise it can clash with third-party libraries.
+    When enabled this option relaxes this restriction.
+
 .. rts-flag:: -I ⟨seconds⟩
 
     :default: 0.3 seconds in the threaded runtime, 0 in the non-threaded runtime

rts/RtsFlags.c

@@ -346,6 +346,10 @@ usage_text[] = {
 "  -xb<addr> Sets the address from which a suitable start for the heap memory",
 "            will be searched from. This is useful if the default address",
 "            clashes with some third-party library.",
+"  --arbitrary-heap-start",
+"            By default heap base offset for the garbage collector is selected above 0x200000000",
+"            because otherwise it can clash with third-party libraries.",
+"            When enabled this option relaxes this restriction.",
 "  -xn       Use the non-moving collector for the old generation.",
 "  -m<n>     Minimum % of heap which must be available (default 3%)",
 "  -G<n>     Number of generations (default: 2)",