beam_validator: Reject functions with more than MAX_ARG arguments

lib/compiler/src/beam_validator.erl

@@ -82,6 +82,12 @@ format_error({{_M,F,A},{I,Off,Desc}}) ->
       "  Internal consistency check failed - please report this bug.~n"
       "  Instruction: ~p~n"
       "  Error:       ~p:~n", [F,A,Off,I,Desc]);
+format_error({{_M,F,A},too_many_arguments}) ->
+    %% The linter rejects user-provided functions that violate this, leaving
+    %% only generated functions like funs or comprehensions. This is not
+    %% super-helpful but it's better than nothing.
+    io_lib:format("System limit reached: generated function ~p/~p has too "
+                  "many arguments.", [F, A]);
 format_error(Error) ->
     io_lib:format("~p~n", [Error]).
 
@@ -279,17 +285,13 @@ validate_1(Is, MFA0, Entry, Level, Ft) ->
 
     validate_branches(MFA, Vst).
 
-extract_header([{func_info, {atom,Mod}, {atom,Name}, Arity}=I | Is],
-               MFA0, Entry, Offset, Acc) ->
-    {_, Name, Arity} = MFA0,                    %Assertion.
-    MFA = {Mod, Name, Arity},
-
-    case Is of
-        [{label, Entry} | _] ->
-            Header = reverse(Acc, [I]),
-            {Offset + 1, MFA, Header, Is};
-        _ ->
-            error({MFA, no_entry_label})
+extract_header([{func_info, {atom, Mod}, {atom,Name}, Arity}=I |
+                [{label, Entry} | _]=Is],
+               {_, Name, Arity}, Entry, Offset, Acc) ->
+    MFA = {Mod, Name, Arity} ,
+    case Arity =< ?MAX_FUNC_ARGS of
+        true -> {Offset + 1, MFA, reverse(Acc, [I]), Is};
+        false -> error({MFA, too_many_arguments})
     end;
 extract_header([{label,_}=I | Is], MFA, Entry, Offset, Acc) ->
     extract_header(Is, MFA, Entry, Offset + 1, [I | Acc]);

lib/compiler/test/beam_validator_SUITE.erl

@@ -44,7 +44,7 @@
          infer_relops/1,
          not_equal_inference/1,bad_bin_unit/1,singleton_inference/1,
          inert_update_type/1,range_inference/1,
-         bif_inference/1]).
+         bif_inference/1,too_many_arguments/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -82,7 +82,7 @@ groups() ->
        container_performance,infer_relops,
        not_equal_inference,bad_bin_unit,singleton_inference,
        inert_update_type,range_inference,
-       bif_inference]}].
+       bif_inference,too_many_arguments]}].
 
 init_per_suite(Config) ->
     test_lib:recompile(?MODULE),
@@ -342,7 +342,7 @@ undef_label(Config) when is_list(Config) ->
 	 5},
     Errors = beam_val(M),
     [{{undef_label,t,1},{undef_labels,[42]}},
-     {{undef_label,x,1},no_entry_label}] = Errors,
+     {{undef_label,x,1},invalid_function_header}] = Errors,
     ok.
 
 illegal_instruction(Config) when is_list(Config) ->
@@ -1160,5 +1160,28 @@ bif_inference_is_function(A, A)  when A orelse ok; is_function(A) ->
 bif_inference_is_function(_, _) ->
     error.
 
+%% GH-9113: We didn't reject funs, comprehensions, and the likes which exceeded
+%% the argument limit.
+too_many_arguments(_Config) ->
+    M = {too_many_arguments,
+         [{t,256},{t,0}],
+         [],
+         [{function,t,256,2,
+           [{label,1},
+            {func_info,{atom,too_many_arguments},{atom,t},256},
+            {label,2},
+            return]},
+          {function,t,0,4,
+           [{label,3},
+            %% Mismatching arity.
+            {func_info,{atom,too_many_arguments},{atom,t},5},
+            {label,4},
+            return]}],
+         5},
+    Errors = beam_val(M),
+    [{{too_many_arguments,t,256},too_many_arguments},
+     {{too_many_arguments,t,0},invalid_function_header}] = Errors,
+    ok.
+
 id(I) ->
     I.

system/doc/efficiency_guide/system_limits.md

@@ -82,7 +82,10 @@ on a 32 bit system at most `2²⁸ - 1`.
 open files and sockets depends on [the maximum number of Erlang ports](#ports)
 available, as well as on operating system-specific settings and limits.
 
-- **Number of arguments to a function or fun** - 255.
+- **Number of arguments to a function** - 255.
+
+- **Number of arguments to a fun** - 255, minus one for each environment
+variable.
 
 - [](){: #unique_references } **Unique References on a Runtime System Instance** -
 Each scheduler thread has its own set of references, and all other threads have