Fix type-checking of variable used in zero-width bit syntax construction

<<A:0>> will always produce an empty binary, regardless of the
type of A. The bug is in the run-time system. Fix it so that a
non-numeric value for A will cause a badarg exception.

Reported-by: Zvi

2 files changed, 26 insertions, 9 deletions

diff --git a/erts/emulator/beam/erl_bits.c b/erts/emulator/beam/erl_bits.c
index 88d2c06246..6f8a7436d5 100644
--- a/erts/emulator/beam/erl_bits.c
+++ b/erts/emulator/beam/erl_bits.c
@@ -555,10 +555,11 @@ fmt_int(byte *buf, Uint sz, Eterm val, Uint size, Uint flags)
 {
     unsigned long offs;
 
-    ASSERT(size != 0);
     offs = BIT_OFFSET(size);
     if (is_small(val)) {
 	Sint v = signed_val(val);
+
+	ASSERT(size != 0);	  /* Tested by caller */
 	if (flags & BSF_LITTLE) { /* Little endian */
 	    sz--;
 	    COPY_VAL(buf,1,v,sz);
@@ -578,6 +579,9 @@ fmt_int(byte *buf, Uint sz, Eterm val, Uint size, Uint flags)
 	ErtsDigit* dp = big_v(val);
 	int n = MIN(sz,ds);
 
+	if (size == 0) {
+	    return 0;
+	}
 	if (flags & BSF_LITTLE) {
 	    sz -= n;                       /* pad with this amount */
 	    if (sign) {
@@ -729,15 +733,13 @@ erts_new_bs_put_integer(ERL_BITS_PROTO_3(Eterm arg, Uint num_bits, unsigned flag
     Uint b;
     byte *iptr;
 
-    if (num_bits == 0) {
-	return 1;
-    }
-
     bit_offset = BIT_OFFSET(bin_offset);
     if (is_small(arg)) {
 	Uint rbits = 8 - bit_offset;
 
-	if (bit_offset + num_bits <= 8) {
+	if (num_bits == 0) {
+	    return 1;
+	} else if (bit_offset + num_bits <= 8) {
 	    /*
 	     * All bits are in the same byte.
 	     */ 
diff --git a/erts/emulator/test/bs_construct_SUITE.erl b/erts/emulator/test/bs_construct_SUITE.erl
index 3d9b51d278..138a19a626 100644
--- a/erts/emulator/test/bs_construct_SUITE.erl
+++ b/erts/emulator/test/bs_construct_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1999-2009. All Rights Reserved.
+%% Copyright Ericsson AB 1999-2010. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -27,7 +27,7 @@
 	 mem_leak/1, coerce_to_float/1, bjorn/1,
 	 huge_float_field/1, huge_binary/1, system_limit/1, badarg/1,
 	 copy_writable_binary/1, kostis/1, dynamic/1, bs_add/1,
-	 otp_7422/1]).
+	 otp_7422/1, zero_width/1]).
 
 -include("test_server.hrl").
 
@@ -36,7 +36,7 @@ all(suite) ->
      not_used, in_guard, mem_leak, coerce_to_float, bjorn,
      huge_float_field, huge_binary, system_limit, badarg,
      copy_writable_binary, kostis, dynamic, bs_add,
-     otp_7422].
+     otp_7422, zero_width].
 
 big(1) ->
     57285702734876389752897683.
@@ -786,5 +786,20 @@ otp_7422_bin(N) when N < 512 ->
 	       end),
     otp_7422_bin(N+1);
 otp_7422_bin(_) -> ok.
+
+zero_width(Config) when is_list(Config) ->
+    ?line Z = id(0),
+    Small = id(42),
+    Big = id(1 bsl 128),
+    ?line <<>> = <<Small:Z>>,
+    ?line <<>> = <<Small:0>>,
+    ?line <<>> = <<Big:Z>>,
+    ?line <<>> = <<Big:0>>,
+    
+    ?line {'EXIT',{badarg,_}} = (catch <<not_a_number:0>>),
+    ?line {'EXIT',{badarg,_}} = (catch <<(id(not_a_number)):Z>>),
+    ?line {'EXIT',{badarg,_}} = (catch <<(id(not_a_number)):0>>),
+
+    ok.
     
 id(I) -> I.