Merge branch 'john/erts/remove-destructive-bs_get_binary2/ERL-901'

* john/erts/remove-destructive-bs_get_binary2/ERL-901: erts: Remove unsafe bs_get_binary2 optimization from loader
kamalogudah · Mar 28, 2019 · 2367dc1 · 2367dc1
2 parents 2f87909 + 0398c68
commit 2367dc1
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Showing 4 changed files with 25 additions and 27 deletions.
diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
@@ -3354,19 +3354,12 @@ gen_get_binary2(LoaderState* stp, GenOpArg Fail, GenOpArg Ms, GenOpArg Live,
 
     NATIVE_ENDIAN(Flags);
     if (Size.type == TAG_a && Size.val == am_all) {
-	if (Ms.type == Dst.type && Ms.val == Dst.val) {
-	    GENOP_NAME_ARITY(op, i_bs_get_binary_all_reuse, 3);
-	    op->a[0] = Ms;
-	    op->a[1] = Fail;
-	    op->a[2] = Unit;
-	} else {
-	    GENOP_NAME_ARITY(op, i_bs_get_binary_all2, 5);
-	    op->a[0] = Ms;
-	    op->a[1] = Fail;
-	    op->a[2] = Live;
-	    op->a[3] = Unit;
-	    op->a[4] = Dst;
-	}
+	GENOP_NAME_ARITY(op, i_bs_get_binary_all2, 5);
+	op->a[0] = Ms;
+	op->a[1] = Fail;
+	op->a[2] = Live;
+	op->a[3] = Unit;
+	op->a[4] = Dst;
     } else if (Size.type == TAG_i) {
 	GENOP_NAME_ARITY(op, i_bs_get_binary_imm2, 6);
 	op->a[0] = Ms;

diff --git a/erts/emulator/beam/bs_instrs.tab b/erts/emulator/beam/bs_instrs.tab
@@ -1136,7 +1136,6 @@ i_bs_get_utf16.execute(Fail, Flags, Dst) {
 }
 
 bs_context_to_binary := ctx_to_bin.fetch.execute;
-i_bs_get_binary_all_reuse := ctx_to_bin.fetch_bin.execute;
 
 ctx_to_bin.head() {
     Eterm context;
@@ -1159,16 +1158,6 @@ ctx_to_bin.fetch(Src) {
     }
 }
 
-ctx_to_bin.fetch_bin(Src, Fail, Unit) {
-    context = $Src;
-    mb = ms_matchbuffer(context);
-    size = mb->size - mb->offset;
-    if (size % $Unit != 0) {
-        $FAIL($Fail);
-    }
-    offs = mb->offset;
-}
-
 ctx_to_bin.execute() {
     Uint hole_size;
     Uint orig = mb->orig;

diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
@@ -1262,7 +1262,6 @@ bs_get_binary2 Fail=f Ms=xy Live=u Sz=sq Unit=u Flags=u Dst=d => \
 i_bs_get_binary_imm2 xy f? t W t d
 i_bs_get_binary2 xy f t? s t d
 i_bs_get_binary_all2 xy f? t t d
-i_bs_get_binary_all_reuse xy f? t
 
 # Fetching float from binaries.
 bs_get_float2 Fail=f Ms=xy Live=u Sz=s Unit=u Flags=u Dst=d => \

diff --git a/erts/emulator/test/bs_match_misc_SUITE.erl b/erts/emulator/test/bs_match_misc_SUITE.erl
@@ -24,7 +24,7 @@
 	 kenneth/1,encode_binary/1,native/1,happi/1,
 	 size_var/1,wiger/1,x0_context/1,huge_float_field/1,
 	 writable_binary_matched/1,otp_7198/1,unordered_bindings/1,
-	 float_middle_endian/1]).
+	 float_middle_endian/1,unsafe_get_binary_reuse/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -36,7 +36,8 @@ all() ->
     [bound_var, bound_tail, t_float, little_float, sean,
      kenneth, encode_binary, native, happi, size_var, wiger,
      x0_context, huge_float_field, writable_binary_matched,
-     otp_7198, unordered_bindings, float_middle_endian].
+     otp_7198, unordered_bindings, float_middle_endian,
+     unsafe_get_binary_reuse].
 
 
 %% Test matching of bound variables.
@@ -556,5 +557,21 @@ unordered_bindings(CompressedLength, HashSize, PadLength, T) ->
      Padding:PadLength/binary,PadLength>> = T,
     {Content,Mac,Padding}.
 
+%% ERL-901: A load-time optimization assumed that match contexts had no further
+%% uses when a bs_get_binary2 overwrote the match context's register, and
+%% figured it would be safe to reuse the match context's memory for the
+%% resulting binary.
+%%
+%% This is no longer safe as of OTP 22, as a match context may be reused after
+%% being passed to another function.
+unsafe_get_binary_reuse(Config) when is_list(Config) ->
+    <<_First, Rest/binary>> = <<"hello">>,
+    ubgr_1(Rest),
+    <<Second,_/bits>> = Rest,
+    $e = Second,
+    ok.
+
+ubgr_1(<<_CP/utf8, Rest/binary>>) -> id(Rest);
+ubgr_1(_) -> false.
 
 id(I) -> I.