Eliminate internal error in beam_validator

`beam_validator` and `beam_disasm` assumed that there could only be one `get_tail` command in a `bs_match` instruction. That assumption is wrong. In rare circumstances, there can be more than one. Closes #6551
erlang · Dec 15, 2022 · 8df1a6c · 8df1a6c
1 parent 6cbbb5d
commit 8df1a6c
Show file tree

Hide file tree

Showing 3 changed files with 37 additions and 10 deletions.
diff --git a/lib/compiler/src/beam_disasm.erl b/lib/compiler/src/beam_disasm.erl
@@ -1363,8 +1363,8 @@ resolve_bs_match_commands([{atom,'=:='},nil,Bits,Value|Rest]) ->
     [{'=:=',nil,Bits,Value} | resolve_bs_match_commands(Rest)];
 resolve_bs_match_commands([{atom,skip},Stride|Rest]) ->
     [{skip,Stride} | resolve_bs_match_commands(Rest)];
-resolve_bs_match_commands([{atom,get_tail},Live,Src,Dst]) ->
-    [{get_tail,Live,Src,Dst}];
+resolve_bs_match_commands([{atom,get_tail},Live,Src,Dst|Rest]) ->
+    [{get_tail,Live,Src,Dst} | resolve_bs_match_commands(Rest)];
 resolve_bs_match_commands([]) ->
     [].
 

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
@@ -1705,13 +1705,6 @@ validate_bs_start_match({f,Fail}, Live, Src, Dst, Vst) ->
 %% Validate the bs_match instruction.
 %%
 
-validate_bs_match([{get_tail,Live,_,Dst}], Ctx, _, Vst0) ->
-    validate_ctx_live(Ctx, Live),
-    verify_live(Live, Vst0),
-    Vst = prune_x_regs(Live, Vst0),
-    #t_bs_context{tail_unit=Unit} = get_concrete_type(Ctx, Vst0),
-    Type = #t_bitstring{size_unit=Unit},
-    extract_term(Type, get_tail, [Ctx], Dst, Vst, Vst0);
 validate_bs_match([I|Is], Ctx, Unit0, Vst0) ->
     case I of
         {ensure_at_least,_Size,Unit} ->
@@ -1739,7 +1732,16 @@ validate_bs_match([I|Is], Ctx, Unit0, Vst0) ->
             Vst = extract_term(Type, bs_match, [Ctx], Dst, Vst1, Vst0),
             validate_bs_match(Is, Ctx, Unit0, Vst);
         {skip,_Stride} ->
-            validate_bs_match(Is, Ctx, Unit0, Vst0)
+            validate_bs_match(Is, Ctx, Unit0, Vst0);
+        {get_tail,Live,_,Dst} ->
+            validate_ctx_live(Ctx, Live),
+            verify_live(Live, Vst0),
+            Vst1 = prune_x_regs(Live, Vst0),
+            #t_bs_context{tail_unit=Unit} = get_concrete_type(Ctx, Vst0),
+            Type = #t_bitstring{size_unit=Unit},
+            Vst = extract_term(Type, get_tail, [Ctx], Dst, Vst1, Vst0),
+            %% In rare circumstance, there can be multiple `get_tail` sub commands.
+            validate_bs_match(Is, Ctx, Unit, Vst)
     end;
 validate_bs_match([], _Ctx, _Unit, Vst) ->
     Vst.

diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
@@ -2675,6 +2675,13 @@ bs_match(_Config) ->
     <<1,0>> = do_bs_match_1(whatever, <<1,0>>),
     <<1,1>> = do_bs_match_1(whatever, <<1,1>>),
     {a,b,c} = do_bs_match_1(whatever, {a,b,c}),
+
+    {'EXIT',{badarg,_}} = catch do_bs_match_gh_6551a(<<>>),
+    false = do_bs_match_gh_6551a(<<42>>),
+
+    {0,0} = do_bs_match_gh_6551b(0),
+    {<<42>>,<<42>>} = do_bs_match_gh_6551b(<<42>>),
+
     ok.
 
 do_bs_match_1(_, X) ->
@@ -2686,6 +2693,24 @@ do_bs_match_1(_, X) ->
     end,
     X.
 
+do_bs_match_gh_6551a(X) ->
+    case X of
+        <<>> ->
+            true -- [];
+        <<_>> ->
+            X
+    end /= X.
+
+
+do_bs_match_gh_6551b(X) ->
+    {X,
+        case X of
+            0 ->
+                0;
+            <<_>> ->
+                X
+        end}.
+
 %% GH-6348/OTP-18297: Allow aliases for binaries.
 -record(ba_foo, {a,b,c}).