[PATCH] D119426: [C++20] [Modules] Check if modulemap exists to avoid crash in implicit used C++ module

Zezheng Li via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu Feb 10 04:03:00 PST 2022

ZezhengLi created this revision.
ZezhengLi added reviewers: ChuanqiXu, rsmith, urnathan.
ZezhengLi added a project: clang.
ZezhengLi requested review of this revision.
Herald added a subscriber: cfe-commits.

An impilt used of module without prebuild path may cause crash.

For example:

  // ./dir1/C.cppm
  export module C;
  // ./dir2/B.cppm
  export module B;
  import C;
  // ./A.cpp
  import B;
  import C;

When we compile A.cpp without the prebuild path of C.pcm, the compiler will crash.

  clang++ -std=c++20 --precompile -c ./dir1/C.cppm -o dir1/C.pcm
  clang++ -std=c++20 --precompile -fprebuilt-module-path=./dir2  -c B.cppm -o B.pcm
  clang++ -std=c++20 -fprebuilt-module-path=./dir2 A.cpp

The prebuilt path of module C is cached when import module B, and in the function HeaderSearch::getCachedModuleFileName, the compiler try to get the filename by modulemap without check if modulemap exists,and there is no modulemap in C++ module.

  rG LLVM Github Monorepo



Index: clang/test/Modules/implicit-module-with-missing-path.cpp
--- /dev/null
+++ clang/test/Modules/implicit-module-with-missing-path.cpp
@@ -0,0 +1,12 @@
+// This tests that the compiler wouldn't crash if the module path misses
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/subdir
+// RUN: echo "export module C;" >> %t/subdir/C.cppm
+// RUN: echo -e "export module B;\nimport C;" >> %t/B.cppm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface %t/subdir/C.cppm -o %t/subdir/C.pcm
+// RUN: %clang_cc1 -std=c++20 -emit-module-interface -fprebuilt-module-path=%t/subdir %t/B.cppm -o %t/B.pcm
+// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t %s -fsyntax-only -verify
+import B;
+import C; // expected-error {{module 'C' is needed but has not been provided, and implicit use of module files is disabled}}
\ No newline at end of file
Index: clang/lib/Lex/HeaderSearch.cpp
--- clang/lib/Lex/HeaderSearch.cpp
+++ clang/lib/Lex/HeaderSearch.cpp
@@ -172,6 +172,10 @@
 std::string HeaderSearch::getCachedModuleFileName(Module *Module) {
   const FileEntry *ModuleMap =
+  // The ModuleMap maybe a nullptr, when we load a cached C++ module without
+  // *.modulemap file. In this case, just return an empty string.
+  if (ModuleMap == nullptr)
+    return {};
   return getCachedModuleFileName(Module->Name, ModuleMap->getName());

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