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LLVM libc clang-tidy checks
These are the clang-tidy checks designed to help enforce implementation
The configuration file is ``src/.clang-tidy``.
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.
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) {}
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.
There are exceptions for the following functions:
``__errno_location`` so that ``errno`` can be set;
``malloc``, ``calloc``, ``realloc``, ``aligned_alloc``, and ``free`` since they
are always external and can be intercepted.
.. code-block:: c++
namespace __llvm_libc {
// Allow calls with the fully qualified name.
// Allow calls to compiler provided functions.
// Bare calls are allowed as long as they resolve to the correct namespace.
// Disallow calling into functions in the global namespace.
// Allow calling into specific global functions (explained above)
} // namespace __llvm_libc