From 93c5e457faeccfd8ccbb1e6c587ad6df1f200408 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 21 Aug 2015 07:07:49 +0200
Subject: beam_validator: Don't allow x(1023) to be used

In 45f469ca0890, the BEAM loader started to use x(1023) as scratch
register for some instructions. Therefore we should not allow
x(1023) to be used in code emitted by the compiler.
---
 lib/compiler/src/beam_validator.erl | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

(limited to 'lib/compiler/src/beam_validator.erl')

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 942d69a756..ab5fedf3bf 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -31,8 +31,6 @@
 
 -import(lists, [reverse/1,foldl/3,foreach/2,dropwhile/2]).
 
--define(MAXREG, 1024).
-
 %%-define(DEBUG, 1).
 -ifdef(DEBUG).
 -define(DBG_FORMAT(F, D), (io:format((F), (D)))).
@@ -970,9 +968,9 @@ get_fls(#vst{current=#st{fls=Fls}}) when is_atom(Fls) -> Fls.
 
 init_fregs() -> 0.
 
-set_freg({fr,Fr}, #vst{current=#st{f=Fregs0}=St}=Vst)
+set_freg({fr,Fr}=Freg, #vst{current=#st{f=Fregs0}=St}=Vst)
   when is_integer(Fr), 0 =< Fr ->
-    limit_check(Fr),
+    check_limit(Freg),
     Bit = 1 bsl Fr,
     if
 	Fregs0 band Bit =:= 0 ->
@@ -985,9 +983,10 @@ set_freg(Fr, _) -> error({bad_target,Fr}).
 assert_freg_set({fr,Fr}=Freg, #vst{current=#st{f=Fregs}})
   when is_integer(Fr), 0 =< Fr ->
     if
-	Fregs band (1 bsl Fr) =/= 0 ->
-	    limit_check(Fr);
-	true -> error({uninitialized_reg,Freg})
+	(Fregs bsr Fr) band 1 =:= 0 ->
+	    error({uninitialized_reg,Freg});
+	true ->
+	    ok
     end;
 assert_freg_set(Fr, _) -> error({bad_source,Fr}).
 
@@ -1066,16 +1065,16 @@ set_type(Type, {x,_}=Reg, Vst) -> set_type_reg(Type, Reg, Vst);
 set_type(Type, {y,_}=Reg, Vst) -> set_type_y(Type, Reg, Vst);
 set_type(_, _, #vst{}=Vst) -> Vst.
 
-set_type_reg(Type, {x,X}, #vst{current=#st{x=Xs}=St}=Vst) 
+set_type_reg(Type, {x,X}=Reg, #vst{current=#st{x=Xs}=St}=Vst)
   when is_integer(X), 0 =< X ->
-    limit_check(X),
+    check_limit(Reg),
     Vst#vst{current=St#st{x=gb_trees:enter(X, Type, Xs)}};
 set_type_reg(Type, Reg, Vst) ->
     set_type_y(Type, Reg, Vst).
 
 set_type_y(Type, {y,Y}=Reg, #vst{current=#st{y=Ys0}=St}=Vst)
   when is_integer(Y), 0 =< Y ->
-    limit_check(Y),
+    check_limit(Reg),
     Ys = case gb_trees:lookup(Y, Ys0) of
 	     none ->
 		 error({invalid_store,Reg,Type});
@@ -1591,9 +1590,15 @@ return_type_math(pow, 2) -> {float,[]};
 return_type_math(pi, 0) -> {float,[]};
 return_type_math(F, A) when is_atom(F), is_integer(A), A >= 0 -> term.
 
-limit_check(Num) when is_integer(Num), Num >= ?MAXREG ->
-    error(limit);
-limit_check(_) -> ok.
+check_limit({x,X}) when is_integer(X), X < 1023 ->
+    %% Note: x(1023) is reserved for use by the BEAM loader.
+    ok;
+check_limit({y,Y}) when is_integer(Y), Y < 1024 ->
+    ok;
+check_limit({fr,Fr}) when is_integer(Fr), Fr < 1024 ->
+    ok;
+check_limit(_) ->
+    error(limit).
 
 min(A, B) when is_integer(A), is_integer(B), A < B -> A;
 min(A, B) when is_integer(A), is_integer(B) -> B.
-- 
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