[libcxx-commits] [libcxx] [libc++] Add unsafe-buffer-usage attributes to span, vector, string and string_view (PR #119603)

[via libcxx-commits]

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@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: gcc
+
+// Make sure that std::string's operations produce unsafe buffer access warnings when
+// -Wunsafe-buffer-usage is used, when hardening is disabled.
+//
+// Note: We disable _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER to ensure that the libc++
+//       headers are considered system headers, to validate that users would get
+//       those diagnostics.
+//
+// ADDITIONAL_COMPILE_FLAGS: -Wunsafe-buffer-usage -U_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+// REQUIRES: libcpp-hardening-mode=none
+
+#include <string>
+#include <cstddef>
+
+void f(std::string s, std::string const cs, std::size_t n) {
+  (void)s[n];       // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)cs[n];      // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)s.front();  // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)cs.front(); // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)s.back();   // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)cs.back();  // expected-warning {{function introduces unsafe buffer manipulation}}
+  s.pop_back();     // expected-warning {{function introduces unsafe buffer manipulation}}
+
+  auto it = s.begin();
+#if defined(_LIBCPP_ABI_BOUNDED_ITERATORS_IN_STRING)
+  (void)*it;   // nothing
+  (void)it[n]; // nothing
+#else
+  (void)*it;   // expected-warning {{function introduces unsafe buffer manipulation}}
+  (void)it[n]; // expected-warning {{function introduces unsafe buffer manipulation}}
+#endif
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geoffreygaren wrote:

...and my reading of the spec says that merely adjusting an iterator past the end or prior to the beginning is undef, even if you don't dereference it.

https://github.com/llvm/llvm-project/pull/119603