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