c: Add Walloc-size to warn about insufficient size in allocations [PR71219]

Add option Walloc-size that warns about allocations that have
insufficient storage for the target type of the pointer the
storage is assigned to. Added to Wextra.

	PR c/71219
gcc:
	* doc/invoke.texi: Document -Walloc-size option.

gcc/c-family:

	* c.opt (Walloc-size): New option.

gcc/c:
	* c-typeck.cc (convert_for_assignment): Add warning.

gcc/testsuite:

	* gcc.dg/Walloc-size-1.c: New test.
	* gcc.dg/Walloc-size-2.c: New test.

5 files changed, 94 insertions, 0 deletions

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 44b9c86..29d3d78 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -331,6 +331,10 @@ Walloca
 C ObjC C++ ObjC++ Var(warn_alloca) Warning
 Warn on any use of alloca.
 
+Walloc-size
+C ObjC Var(warn_alloc_size) Warning LangEnabledBy(C ObjC, Wextra)
+Warn when allocating insufficient storage for the target type of the assigned pointer.
+
 Walloc-size-larger-than=
 C ObjC C++ LTO ObjC++ Var(warn_alloc_size_limit) Joined Host_Wide_Int ByteSize Warning Init(HOST_WIDE_INT_MAX)
 -Walloc-size-larger-than=<bytes>	Warn for calls to allocation functions that
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 0de4662..16fadfb 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -7347,6 +7347,34 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		    "request for implicit conversion "
 		    "from %qT to %qT not permitted in C++", rhstype, type);
 
+      /* Warn of new allocations that are not big enough for the target
+	 type.  */
+      tree fndecl;
+      if (warn_alloc_size
+	  && TREE_CODE (rhs) == CALL_EXPR
+	  && (fndecl = get_callee_fndecl (rhs)) != NULL_TREE
+	  && DECL_IS_MALLOC (fndecl))
+	{
+	  tree fntype = TREE_TYPE (fndecl);
+	  tree fntypeattrs = TYPE_ATTRIBUTES (fntype);
+	  tree alloc_size = lookup_attribute ("alloc_size", fntypeattrs);
+	  if (alloc_size)
+	    {
+	      tree args = TREE_VALUE (alloc_size);
+	      int idx = TREE_INT_CST_LOW (TREE_VALUE (args)) - 1;
+	      /* For calloc only use the second argument.  */
+	      if (TREE_CHAIN (args))
+		idx = TREE_INT_CST_LOW (TREE_VALUE (TREE_CHAIN (args))) - 1;
+	      tree arg = CALL_EXPR_ARG (rhs, idx);
+	      if (TREE_CODE (arg) == INTEGER_CST
+		  && INTEGER_CST == TREE_CODE (TYPE_SIZE_UNIT (ttl))
+		  && tree_int_cst_lt (arg, TYPE_SIZE_UNIT (ttl)))
+		 warning_at (location, OPT_Walloc_size, "allocation of "
+			     "insufficient size %qE for type %qT with "
+			     "size %qE", arg, ttl, TYPE_SIZE_UNIT (ttl));
+	    }
+	}
+
       /* See if the pointers point to incompatible address spaces.  */
       asl = TYPE_ADDR_SPACE (ttl);
       asr = TYPE_ADDR_SPACE (ttr);
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 53ae784..6e776a0 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8138,6 +8138,16 @@ always leads to a call to another @code{cold} function such as wrappers of
 C++ @code{throw} or fatal error reporting functions leading to @code{abort}.
 @end table
 
+@opindex Wno-alloc-size
+@opindex Walloc-size
+@item -Walloc-size
+Warn about calls to allocation functions decorated with attribute
+@code{alloc_size} that specify insufficient size for the target type of
+the pointer the result is assigned to, including those to the built-in
+forms of the functions @code{aligned_alloc}, @code{alloca},
+@code{calloc},
+@code{malloc}, and @code{realloc}.
+
 @opindex Wno-alloc-zero
 @opindex Walloc-zero
 @item -Walloc-zero
diff --git a/gcc/testsuite/gcc.dg/Walloc-size-1.c b/gcc/testsuite/gcc.dg/Walloc-size-1.c
new file mode 100644
index 0000000..cae5e07
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Walloc-size-1.c
@@ -0,0 +1,34 @@
+/* Tests the warnings for insufficient allocation size.
+   { dg-do compile }
+   { dg-options "-Walloc-size" }
+ * */
+
+struct b { int x[10]; };
+
+void fo0(void)
+{
+        struct b *p = __builtin_malloc(sizeof *p);
+}
+
+void fo1(void)
+{
+        struct b *p = __builtin_malloc(sizeof p);	/* { dg-warning "allocation of insufficient size" } */
+}
+
+void fo2(void)
+{
+        struct b *p = __builtin_alloca(sizeof p);	/* { dg-warning "allocation of insufficient size" } */
+}
+
+void fo3(void)
+{
+        struct b *p = __builtin_calloc(1, sizeof p);	/* { dg-warning "allocation of insufficient size" } */
+}
+
+void g(struct b* p);
+
+void fo4(void)
+{
+        g(__builtin_malloc(4));				/* { dg-warning "allocation of insufficient size" } */
+}
+
diff --git a/gcc/testsuite/gcc.dg/Walloc-size-2.c b/gcc/testsuite/gcc.dg/Walloc-size-2.c
new file mode 100644
index 0000000..de641a6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Walloc-size-2.c
@@ -0,0 +1,18 @@
+/* Test that VLA types do not crash with -Walloc-size
+   { dg-do compile }
+   { dg-options "-Walloc-size" }
+ * */
+
+struct foo { int x[10]; };
+
+void fo0(int n)
+{
+        struct foo (*p)[n] = __builtin_malloc(sizeof *p);
+}
+
+void fo1(int n)
+{
+	struct bar { int x[n]; };
+	struct bar *p = __builtin_malloc(sizeof *p);
+}
+