Merge branch 'john/erts/fix-binary-append-syslimit/OTP-14524' into maint-20

* john/erts/fix-binary-append-syslimit/OTP-14524:
  Check for overflow when appending binaries, and error out with system_limit

# Conflicts:
#	erts/emulator/test/bs_construct_SUITE.erl

1 files changed, 19 insertions, 5 deletions

diff --git a/erts/emulator/test/bs_construct_SUITE.erl b/erts/emulator/test/bs_construct_SUITE.erl
index b79f4b995d..ce50bcdd86 100644
--- a/erts/emulator/test/bs_construct_SUITE.erl
+++ b/erts/emulator/test/bs_construct_SUITE.erl
@@ -905,14 +905,28 @@ bs_add_overflow(_Config) ->
         _ when Memsize < (2 bsl 30) ->
 	    {skip, "Less then 2 GB of memory"};
 	4 ->
-	    Large = <<0:((1 bsl 30)-1)>>,
-	    {'EXIT',{system_limit,_}} =
-		(catch <<Large/bits, Large/bits, Large/bits, Large/bits,
-                         Large/bits, Large/bits, Large/bits, Large/bits,
-                         Large/bits>>),
+            {'EXIT', {system_limit, _}} = (catch bs_add_overflow_signed()),
+            {'EXIT', {system_limit, _}} = (catch bs_add_overflow_unsigned()),
 	    ok
     end.
 
+bs_add_overflow_signed() ->
+    %% Produce a large result of bs_add that, if cast to signed int, would
+    %% overflow into a negative number that fits a smallnum.
+    Large = <<0:((1 bsl 30)-1)>>,
+    <<Large/bits, Large/bits, Large/bits, Large/bits,
+      Large/bits, Large/bits, Large/bits, Large/bits,
+      Large/bits>>.
+
+bs_add_overflow_unsigned() ->
+    %% Produce a large result of bs_add that goes beyond the limit of an
+    %% unsigned word. This used to succeed but produced an incorrect result
+    %% where B =:= C!
+    A = <<0:((1 bsl 32)-8)>>,
+    B = <<2, 3>>,
+    C = <<A/binary,1,B/binary>>,
+    true = byte_size(B) < byte_size(C).
+
 id(I) -> I.
 
 memsize() ->