[clang-tidy] Add module for llvm-libc and restrict-system-libc-header-check.

Summary: This adds a new module to enforce standards specific to the llvm-libc project. This change also adds the first check which restricts user from including system libc headers accidentally which can lead to subtle bugs that would be a challenge to detect.

Reviewers: alexfh, hokein, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: juliehockett, arphaman, jfb, abrachet, sivachandra, Eugene.Zelenko, njames93, mgorny, xazax.hun, MaskRay, cfe-commits

Tags: #clang-tools-extra, #libc-project, #clang

Differential Revision: https://reviews.llvm.org/D75332

clang-tools-extra/clang-tidy/CMakeLists.txt

@@ -51,6 +51,7 @@ add_subdirectory(google)
 add_subdirectory(hicpp)
 add_subdirectory(linuxkernel)
 add_subdirectory(llvm)
+add_subdirectory(llvmlibc)
 add_subdirectory(misc)
 add_subdirectory(modernize)
 if(CLANG_ENABLE_STATIC_ANALYZER)
@@ -75,6 +76,7 @@ set(ALL_CLANG_TIDY_CHECKS
   clangTidyHICPPModule
   clangTidyLinuxKernelModule
   clangTidyLLVMModule
+  clangTidyLLVMLibcModule
   clangTidyMiscModule
   clangTidyModernizeModule
   clangTidyObjCModule

clang-tools-extra/clang-tidy/ClangTidyForceLinker.h

@@ -45,6 +45,11 @@ extern volatile int LLVMModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED LLVMModuleAnchorDestination =
     LLVMModuleAnchorSource;
 
+// This anchor is used to force the linker to link the LLVMLibcModule.
+extern volatile int LLVMLibcModuleAnchorSource;
+static int LLVM_ATTRIBUTE_UNUSED LLVMLibcModuleAnchorDestination =
+    LLVMLibcModuleAnchorSource;
+
 // This anchor is used to force the linker to link the CppCoreGuidelinesModule.
 extern volatile int CppCoreGuidelinesModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED CppCoreGuidelinesModuleAnchorDestination =

clang-tools-extra/clang-tidy/llvmlibc/CMakeLists.txt

@@ -0,0 +1,15 @@
+set(LLVM_LINK_COMPONENTS support)
+
+add_clang_library(clangTidyLLVMLibcModule
+  LLVMLibcTidyModule.cpp
+  RestrictSystemLibcHeadersCheck.cpp
+
+  LINK_LIBS
+  clangAST
+  clangASTMatchers
+  clangBasic
+  clangLex
+  clangTidy
+  clangTidyUtils
+  clangTooling
+  )

clang-tools-extra/clang-tidy/llvmlibc/LLVMLibcTidyModule.cpp

@@ -0,0 +1,37 @@
+//===--- LLVMLibcTidyModule.cpp - clang-tidy ------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "../ClangTidy.h"
+#include "../ClangTidyModule.h"
+#include "../ClangTidyModuleRegistry.h"
+#include "RestrictSystemLibcHeadersCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace llvm_libc {
+
+class LLVMLibcModule : public ClangTidyModule {
+public:
+  void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<RestrictSystemLibcHeadersCheck>(
+        "llvmlibc-restrict-system-libc-headers");
+  }
+};
+
+// Register the LLVMLibcTidyModule using this statically initialized variable.
+static ClangTidyModuleRegistry::Add<LLVMLibcModule>
+    X("llvmlibc-module", "Adds LLVM libc standards checks.");
+
+} // namespace llvm_libc
+
+// This anchor is used to force the linker to link in the generated object file
+// and thus register the LLVMLibcModule.
+volatile int LLVMLibcModuleAnchorSource = 0;
+
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/llvmlibc/RestrictSystemLibcHeadersCheck.cpp

@@ -0,0 +1,73 @@
+//===--- RestrictSystemLibcHeadersCheck.cpp - clang-tidy ------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "RestrictSystemLibcHeadersCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/HeaderSearch.h"
+#include "clang/Lex/HeaderSearchOptions.h"
+
+namespace clang {
+namespace tidy {
+namespace llvm_libc {
+
+namespace {
+
+class RestrictedIncludesPPCallbacks : public PPCallbacks {
+public:
+  explicit RestrictedIncludesPPCallbacks(
+      RestrictSystemLibcHeadersCheck &Check, const SourceManager &SM,
+      const SmallString<128> CompilerIncudeDir)
+      : Check(Check), SM(SM), CompilerIncudeDir(CompilerIncudeDir) {}
+
+  void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,
+                          StringRef FileName, bool IsAngled,
+                          CharSourceRange FilenameRange, const FileEntry *File,
+                          StringRef SearchPath, StringRef RelativePath,
+                          const Module *Imported,
+                          SrcMgr::CharacteristicKind FileType) override;
+
+private:
+  RestrictSystemLibcHeadersCheck &Check;
+  const SourceManager &SM;
+  const SmallString<128> CompilerIncudeDir;
+};
+
+} // namespace
+
+void RestrictedIncludesPPCallbacks::InclusionDirective(
+    SourceLocation HashLoc, const Token &IncludeTok, StringRef FileName,
+    bool IsAngled, CharSourceRange FilenameRange, const FileEntry *File,
+    StringRef SearchPath, StringRef RelativePath, const Module *Imported,
+    SrcMgr::CharacteristicKind FileType) {
+  if (SrcMgr::isSystem(FileType)) {
+    // Compiler provided headers are allowed (e.g stddef.h).
+    if (SearchPath == CompilerIncudeDir) return;
+    if (!SM.isInMainFile(HashLoc)) {
+      Check.diag(
+          HashLoc,
+          "system libc header %0 not allowed, transitively included from %1")
+          << FileName << SM.getFilename(HashLoc);
+    } else {
+      Check.diag(HashLoc, "system libc header %0 not allowed") << FileName;
+    }
+  }
+}
+
+void RestrictSystemLibcHeadersCheck::registerPPCallbacks(
+    const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
+  SmallString<128> CompilerIncudeDir =
+      StringRef(PP->getHeaderSearchInfo().getHeaderSearchOpts().ResourceDir);
+  llvm::sys::path::append(CompilerIncudeDir, "include");
+  PP->addPPCallbacks(std::make_unique<RestrictedIncludesPPCallbacks>(
+      *this, SM, CompilerIncudeDir));
+}
+
+} // namespace llvm_libc
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/llvmlibc/RestrictSystemLibcHeadersCheck.h

@@ -0,0 +1,35 @@
+//===--- RestrictSystemLibcHeadersCheck.h - clang-tidy ----------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVMLIBC_RESTRICTSYSTEMLIBCHEADERSCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVMLIBC_RESTRICTSYSTEMLIBCHEADERSCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace llvm_libc {
+
+/// Warns of accidental inclusions of system libc headers that aren't
+/// compiler provided.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/llvmlibc-restrict-system-libc-headers.html
+class RestrictSystemLibcHeadersCheck : public ClangTidyCheck {
+public:
+  RestrictSystemLibcHeadersCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+                           Preprocessor *ModuleExpanderPP) override;
+};
+
+} // namespace llvm_libc
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_LLVMLIBC_RESTRICTSYSTEMLIBCHEADERSCHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -67,6 +67,12 @@ The improvements are...
 Improvements to clang-tidy
 --------------------------
 
+New module
+^^^^^^^^^^
+- New module `llvmlibc`.
+
+  This module contains checks related to the LLVM-libc coding standards.
+
 New checks
 ^^^^^^^^^^
 
@@ -95,6 +101,12 @@ New checks
   Flags use of the `C` standard library functions ``memset``, ``memcpy`` and
   ``memcmp`` and similar derivatives on non-trivial types.
 
+- New :doc:`llvmlibc-restrict-system-libc-headers
+  <clang-tidy/checks/llvmlibc-restrict-system-libc-headers>` check.
+
+  Finds includes of system libc headers not provided by the compiler within
+  llvm-libc implementations.
+
 - New :doc:`objc-dealloc-in-category
   <clang-tidy/checks/objc-dealloc-in-category>` check.
 

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -187,6 +187,7 @@ Clang-Tidy Checks
    `llvm-prefer-isa-or-dyn-cast-in-conditionals <llvm-prefer-isa-or-dyn-cast-in-conditionals.html>`_, "Yes"
    `llvm-prefer-register-over-unsigned <llvm-prefer-register-over-unsigned.html>`_, "Yes"
    `llvm-twine-local <llvm-twine-local.html>`_, "Yes"
+   `llvmlibc-restrict-system-libc-headers <llvmlibc-restrict-system-libc-headers.html>`_,
    `misc-definitions-in-headers <misc-definitions-in-headers.html>`_, "Yes"
    `misc-misplaced-const <misc-misplaced-const.html>`_,
    `misc-new-delete-overloads <misc-new-delete-overloads.html>`_,

clang-tools-extra/docs/clang-tidy/checks/llvmlibc-restrict-system-libc-headers.rst

@@ -0,0 +1,20 @@
+.. title:: clang-tidy - llvmlibc-restrict-system-libc-headers
+
+llvmlibc-restrict-system-libc-headers
+=====================================
+
+Finds includes of system libc headers not provided by the compiler within
+llvm-libc implementations.
+
+.. 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.
+
+
+This check is necessary because accidentally including system libc headers can
+lead to subtle and hard to detect bugs. For example consider a system libc
+whose ``dirent`` struct has slightly different field ordering than llvm-libc.
+While this will compile successfully, this can cause issues during runtime
+because they are ABI incompatible.

clang-tools-extra/docs/clang-tidy/index.rst

@@ -68,6 +68,7 @@ Name prefix            Description
 ``google-``            Checks related to Google coding conventions.
 ``hicpp-``             Checks related to High Integrity C++ Coding Standard.
 ``llvm-``              Checks related to the LLVM coding conventions.
+``llvmlibc-``          Checks related to the LLVM-libc coding standards.
 ``misc-``              Checks that we didn't have a better category for.
 ``modernize-``         Checks that advocate usage of modern (currently "modern"
                        means "C++11") language constructs.

clang-tools-extra/test/clang-tidy/checkers/Inputs/llvmlibc/transitive.h

@@ -0,0 +1 @@
+#include <math.h>

clang-tools-extra/test/clang-tidy/checkers/llvmlibc-restrict-system-libc-headers-transitive.cpp

@@ -0,0 +1,8 @@
+// RUN: %check_clang_tidy %s llvmlibc-restrict-system-libc-headers %t \
+// RUN:   -- -header-filter=.* \
+// RUN:   -- -I %S/Inputs/llvmlibc \
+// RUN:   -isystem %S/Inputs/llvmlibc/system \
+// RUN:   -resource-dir %S/Inputs/llvmlibc/resource
+
+#include "transitive.h"
+// CHECK-MESSAGES: :1:1: warning: system libc header math.h not allowed, transitively included from {{.*}}

clang-tools-extra/test/clang-tidy/checkers/llvmlibc-restrict-system-libc-headers.cpp

@@ -0,0 +1,13 @@
+// RUN: %check_clang_tidy %s llvmlibc-restrict-system-libc-headers %t \
+// RUN:   -- -- -isystem %S/Inputs/llvmlibc/system \
+// RUN:   -resource-dir %S/Inputs/llvmlibc/resource
+
+#include <stdio.h>
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: system libc header stdio.h not allowed
+#include <stdlib.h>
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: system libc header stdlib.h not allowed
+#include "string.h"
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: system libc header string.h not allowed
+#include "stdatomic.h"
+#include <stddef.h>
+// Compiler provided headers should not throw warnings.