ubsan: Avoid narrowing of multiply for -fsanitize=signed-integer-overflow [PR108256]

We shouldn't narrow multiplications originally done in signed types,
because the original multiplication might overflow but the narrowed
one will be done in unsigned arithmetics and will never overflow.

2023-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/108256
	* convert.cc (do_narrow): Punt for MULT_EXPR if original
	type doesn't wrap around and -fsanitize=signed-integer-overflow
	is on.
	* fold-const.cc (fold_unary_loc) <CASE_CONVERT>: Likewise.

	* c-c++-common/ubsan/pr108256.c: New test.

diff --git a/gcc/convert.cc b/gcc/convert.cc
index a882c67d7c13d5cae081c95a29ccb8726b2468d6..fe85bcb3323f52153724949062de31f9712f8ba1 100644 (file)
--- a/gcc/convert.cc
+++ b/gcc/convert.cc
@@ -384,6 +384,14 @@ do_narrow (location_t loc,
       && sanitize_flags_p (SANITIZE_SI_OVERFLOW))
     return NULL_TREE;
 
+  /* Similarly for multiplication, but in that case it can be
+     problematic even if typex is unsigned type - 0xffff * 0xffff
+     overflows in int.  */
+  if (ex_form == MULT_EXPR
+      && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (expr))
+      && sanitize_flags_p (SANITIZE_SI_OVERFLOW))
+    return NULL_TREE;
+
   /* But now perhaps TYPEX is as wide as INPREC.
      In that case, do nothing special here.
      (Otherwise would recurse infinitely in convert.  */

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 9ab76fb1079a674fad03bf90b10494635f3ecba6..9aaea71a2fc4dcb5d4621aabbba54127c24e804a 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -9574,7 +9574,9 @@ fold_unary_loc (location_t loc, enum tree_code code, tree type, tree op0)
       if (INTEGRAL_TYPE_P (type)
          && TREE_CODE (op0) == MULT_EXPR
          && INTEGRAL_TYPE_P (TREE_TYPE (op0))
-         && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (op0)))
+         && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (op0))
+         && (TYPE_OVERFLOW_WRAPS (TREE_TYPE (op0))
+             || !sanitize_flags_p (SANITIZE_SI_OVERFLOW)))
        {
          /* Be careful not to introduce new overflows.  */
          tree mult_type;

diff --git a/gcc/testsuite/c-c++-common/ubsan/pr108256.c b/gcc/testsuite/c-c++-common/ubsan/pr108256.c
new file mode 100644 (file)
index 0000000..c4054aa
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/pr108256.c
@@ -0,0 +1,27 @@
+/* PR sanitizer/108256 */
+/* { dg-do run { target { lp64 || ilp32 } } } */
+/* { dg-options "-fsanitize=signed-integer-overflow" } */
+
+unsigned short
+foo (unsigned short x, unsigned short y)
+{
+  return x * y;
+}
+
+unsigned short
+bar (unsigned short x, unsigned short y)
+{
+  int r = x * y;
+  return r;
+}
+
+int
+main ()
+{
+  volatile unsigned short a = foo (0xffff, 0xffff);
+  volatile unsigned short b = bar (0xfffe, 0xfffe);
+  return 0;
+}
+
+/* { dg-output "signed integer overflow: 65535 \\\* 65535 cannot be represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*signed integer overflow: 65534 \\\* 65534 cannot be represented in type 'int'" } */