[Sema] add -Walloca to flag uses of `alloca`

This CL adds an optional warning to diagnose uses of the
`__builtin_alloca` family of functions. The use of these functions is
discouraged by many, so it seems like a good idea to allow clang to warn
about it.

Patch by Elaina Guan!

Differential Revision: https://reviews.llvm.org/D64883

llvm-svn: 367067

1 files changed, 20 insertions, 0 deletions

diff --git a/clang/test/Sema/warn-alloca.c b/clang/test/Sema/warn-alloca.c
new file mode 100644
index 00000000000..0990e11ef2f
--- /dev/null
+++ b/clang/test/Sema/warn-alloca.c
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -DSILENCE -fsyntax-only -verify -Wall %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Walloca %s
+
+#ifdef SILENCE
+  // expected-no-diagnostics
+#endif
+
+void test1(int a) {
+  __builtin_alloca(a);
+#ifndef SILENCE
+  // expected-warning@-2 {{use of function '__builtin_alloca' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
+#endif
+}
+
+void test2(int a) {
+  __builtin_alloca_with_align(a, 32);
+#ifndef SILENCE
+  // expected-warning@-2 {{use of function '__builtin_alloca_with_align' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
+#endif
+}