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-rw-r--r--erts/emulator/beam/erl_bif_guard.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/erts/emulator/beam/erl_bif_guard.c b/erts/emulator/beam/erl_bif_guard.c
index 8b47db10dd..9e15f4e399 100644
--- a/erts/emulator/beam/erl_bif_guard.c
+++ b/erts/emulator/beam/erl_bif_guard.c
@@ -318,6 +318,10 @@ double_to_integer(Process* p, double x)
* The following code is used when a guard that may build on the
* heap is called directly. They must not use HAlloc(), but must
* do a garbage collection if there is insufficient heap space.
+ *
+ * Important note: All error checking MUST be done before doing
+ * a garbage collection. The compiler assumes that all registers
+ * are still valid if a guard BIF generates an exception.
*/
#define ERTS_NEED_GC(p, need) ((HEAP_LIMIT((p)) - HEAP_TOP((p))) <= (need))