[libc++][hardening] Add an ABI macro `_LIBCPP_ABI_BOUNDED_ITERATORS`.

[var-const]

Summary

Use the new macro instead of _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING.

[var-const]

Note: this patch is split from https://reviews.llvm.org/D151637 (which is a draft but helps see the state towards which this patch is working).

[ldionne]

libcxx/include/__config

197

This is not true right now, so it should be removed.

198

199–200

This is also aspirational so it could be removed (for now).

202–203

This seems simpler but also more accurate.

libcxx/include/__config_site.in

33 ↗

(On Diff #535037)

We generally don't do that for ABI macros (except e.g. _LIBCPP_ABI_FORCE_ITANIUM and _LIBCPP_ABI_FORCE_MICROSOFT which are kind of hacks and don't have the same purpose as other ABI macros). I don't think this is necessary.

[ldionne]

Basically LGTM w/ comments applied, this is pretty straightforward.

[var-const]

Address feedback

[var-const]

Thanks for the feedback!

[var-const]

The CI failure (on Windows) looks unrelated:

ERROR Error uploading artifact states: Put "https://agent.buildkite.com/v3/jobs/0188fe57-a065-42d7-9db7-12f5c85e38c4/artifacts": context deadline exceeded

I'll go ahead and merge this.

libcxx/include/__config

 #  elif defined(__wasm__)
 #    define _LIBCPP_OBJECT_FORMAT_WASM 1
 #  elif defined(_AIX)
 #    define _LIBCPP_OBJECT_FORMAT_XCOFF 1
 #  else
 // ... add new file formats here ...
 #  endif
 
+// ABI {
+
 #  if _LIBCPP_ABI_VERSION >= 2
 // Change short string representation so that string data starts at offset 0,
 // improving its alignment in some cases.
 #    define _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
 // Fix deque iterator type in order to support incomplete types.
 #    define _LIBCPP_ABI_INCOMPLETE_TYPES_IN_DEQUE
 // Fix undefined behavior in how std::list stores its linked nodes.
 #    define _LIBCPP_ABI_LIST_REMOVE_NODE_POINTER_UB

 #    define _LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
 
 // Define a key function for `bad_function_call` in the library, to centralize
 // its vtable and typeinfo to libc++ rather than having all other libraries
 // using that class define their own copies.
 #    define _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
 #  endif
 
+// Changes the iterator type of select containers (see below) to a bounded iterator that keeps track of whether it's
+// within the bounds of the original container and asserts it on every dereference.
+//
+// ABI impact: changes the iterator type of the relevant containers.
+//
+// Supported containers:
+// - `span`;
+// - `string_view`;
+// - `array`.
+// #define _LIBCPP_ABI_BOUNDED_ITERATORS
+
+// } ABI
+
 #  define _LIBCPP_TOSTRING2(x) #x
 #  define _LIBCPP_TOSTRING(x) _LIBCPP_TOSTRING2(x)
 
 // NOLINTNEXTLINE(libcpp-cpp-version-check)
 #  if __cplusplus < 201103L
 #    define _LIBCPP_CXX03_LANG
 #  endif
 

libcxx/include/__debug

 #if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_DEBUG_RANDOMIZE_UNSPECIFIED_STABILITY)
 # define _LIBCPP_DEBUG_RANDOMIZE_UNSPECIFIED_STABILITY
 #endif
 
 #if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_DEBUG_STRICT_WEAK_ORDERING_CHECK)
 # define _LIBCPP_DEBUG_STRICT_WEAK_ORDERING_CHECK
 #endif
 
-#if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING)
-# define _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_ABI_BOUNDED_ITERATORS)
+# define _LIBCPP_ABI_BOUNDED_ITERATORS
 #endif
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 #   define _LIBCPP_DEBUG_ASSERT(x, m) _LIBCPP_ASSERT(::std::__libcpp_is_constant_evaluated() || (x), m)
 #else
 #   define _LIBCPP_DEBUG_ASSERT(x, m) ((void)0)
 #endif
 

libcxx/include/span

//  constants and types
     using element_type           = _Tp;
     using value_type             = remove_cv_t<_Tp>;
     using size_type              = size_t;
     using difference_type        = ptrdiff_t;
     using pointer                = _Tp *;
     using const_pointer          = const _Tp *;
     using reference              = _Tp &;
     using const_reference        = const _Tp &;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using iterator               = __bounded_iter<pointer>;
 #else
     using iterator               = __wrap_iter<pointer>;
 #endif
     using reverse_iterator       = _VSTD::reverse_iterator<iterator>;
 
     static constexpr size_type extent = _Extent;
 
_LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept
         _LIBCPP_ASSERT(!empty(), "span<T, N>::back() on empty span");
         return __data_[size()-1];
     }
 
     _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data_; }
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator begin() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return iterator(this, data());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator end() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return iterator(this, data() + size());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
 
//  constants and types
     using element_type           = _Tp;
     using value_type             = remove_cv_t<_Tp>;
     using size_type              = size_t;
     using difference_type        = ptrdiff_t;
     using pointer                = _Tp *;
     using const_pointer          = const _Tp *;
     using reference              = _Tp &;
     using const_reference        = const _Tp &;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using iterator               = __bounded_iter<pointer>;
 #else
     using iterator               = __wrap_iter<pointer>;
 #endif
     using reverse_iterator       = _VSTD::reverse_iterator<iterator>;
 
     static constexpr size_type extent = dynamic_extent;
 
_LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept
         return __data_[size()-1];
     }
 
 
     _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data_; }
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator begin() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return iterator(this, data());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator end() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return iterator(this, data() + size());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
     _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
 

libcxx/include/string_view

 public:
     // types
     using traits_type            = _Traits;
     using value_type             = _CharT;
     using pointer                = _CharT*;
     using const_pointer          = const _CharT*;
     using reference              = _CharT&;
     using const_reference        = const _CharT&;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using const_iterator         = __bounded_iter<const_pointer>;
 #else
     using const_iterator         = const_pointer; // See [string.view.iterators]
 #endif
     using iterator               = const_iterator;
     using const_reverse_iterator = _VSTD::reverse_iterator<const_iterator>;
     using reverse_iterator       = const_reverse_iterator;
     using size_type              = size_t;
#endif
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator begin()  const _NOEXCEPT { return cbegin(); }
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator end()    const _NOEXCEPT { return cend(); }
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator cbegin() const _NOEXCEPT {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return __data_;
 #endif
     }
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator cend()   const _NOEXCEPT {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return __data_ + __size_;
 #endif
     }
 
     _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_INLINE_VISIBILITY
     const_reverse_iterator rbegin()   const _NOEXCEPT { return const_reverse_iterator(cend()); }