--- /dev/null
+LLVM libc clang-tidy checks
+===========================
+These are the clang-tidy checks designed to help enforce implementation
+standards.
+The configuration file is ``src/.clang-tidy``.
+
+restrict-system-libc-header
+---------------------------
+One of libc-project’s design goals is to use kernel headers and compiler
+provided headers to prevent code duplication on a per platform basis. This
+presents a problem when writing implementations since system libc headers are
+easy to include accidentally and we can't just use the ``-nostdinc`` flag.
+Improperly included system headers can introduce runtime errors because the C
+standard outlines function prototypes and behaviors but doesn’t define
+underlying implementation details such as the layout of a struct.
+
+This check prevents accidental inclusion of system libc headers when writing a
+libc implementation.
+
+.. code-block:: c++
+
+ #include <stdio.h> // Not allowed because it is part of system libc.
+ #include <stddef.h> // Allowed because it is provided by the compiler.
+ #include "internal/stdio.h" // Allowed because it is NOT part of system libc.
+
+
+implementation-in-namespace
+---------------------------
+
+It is part of our implementation standards that all implementation pieces live
+under the ``__llvm_libc`` namespace. This prevents polution of the global
+namespace. Without a formal check to ensure this, an implementation might
+compile and pass unit tests, but not produce a usable libc function.
+
+This check that ensures any function call resolves to a function within the
+``__llvm_libc`` namespace.
+
+.. code-block:: c++
+
+ // Correct: implementation inside the correct namespace.
+ namespace __llvm_libc {
+ void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
+ // Namespaces within __llvm_libc namespace are allowed.
+ namespace inner{
+ int localVar = 0;
+ }
+ // Functions with C linkage are allowed.
+ extern "C" void str_fuzz(){}
+ }
+
+ // Incorrect: implementation not in a namespace.
+ void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
+
+ // Incorrect: outer most namespace is not correct.
+ namespace something_else {
+ void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
+ }
+
+
+callee-namespace
+----------------
+LLVM-libc is distinct because it is designed to maintain interoperability with
+other libc libraries, including the one that lives on the system. This feature
+creates some uncertainty about which library a call resolves to especially when
+a public header with non-namespaced functions like ``string.h`` is included.
+
+This check ensures any function call resolves to a function within the
+__llvm_libc namespace.
+
+.. code-block:: c++
+
+ namespace __llvm_libc {
+
+ // Allow calls with the fully qualified name.
+ __llvm_libc::strlen("hello");
+
+ // Allow calls to compiler provided functions.
+ (void)__builtin_abs(-1);
+
+ // Bare calls are allowed as long as they resolve to the correct namespace.
+ strlen("world");
+
+ // Disallow calling into functions in the global namespace.
+ ::strlen("!");
+
+ } // namespace __llvm_libc