[clang] Fix a segfault when M is a nullptr #130712

matts1 · 2025-03-11T03:44:07Z

If MM->getOwningModule returns nullptr, then isVisible is called with nullptr, which then calls getImportLoc(nullptr)

llvm-project/clang/lib/Lex/PPMacroExpansion.cpp

Line 208 in 077e0c1

if (CurSubmoduleState->VisibleModules.isVisible(MM->getOwningModule())) {

github-actions · 2025-03-11T03:44:28Z

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llvmbot · 2025-03-11T03:44:59Z

@llvm/pr-subscribers-clang-modules

Author: Matt (matts1)

Changes

If MM->getOwningModule returns nullptr, then isVisible is called with nullptr, which then calls getImportLoc(nullptr)

llvm-project/clang/lib/Lex/PPMacroExpansion.cpp

Line 208 in 077e0c1

if (CurSubmoduleState->VisibleModules.isVisible(MM->getOwningModule())) {

Full diff: https://github.com/llvm/llvm-project/pull/130712.diff

1 Files Affected:

(modified) clang/include/clang/Basic/Module.h (+1-1)

diff --git a/clang/include/clang/Basic/Module.h b/clang/include/clang/Basic/Module.h
index 62cc8acf9588b..3d035f0a5f787 100644
--- a/clang/include/clang/Basic/Module.h
+++ b/clang/include/clang/Basic/Module.h
@@ -888,7 +888,7 @@ class VisibleModuleSet {
 
   /// Get the location at which the import of a module was triggered.
   SourceLocation getImportLoc(const Module *M) const {
-    return M->getVisibilityID() < ImportLocs.size()
+    return M && M->getVisibilityID() < ImportLocs.size()
                ? ImportLocs[M->getVisibilityID()]
                : SourceLocation();
   }

llvmbot · 2025-03-11T03:45:00Z

@llvm/pr-subscribers-clang

Author: Matt (matts1)

Changes

If MM->getOwningModule returns nullptr, then isVisible is called with nullptr, which then calls getImportLoc(nullptr)

llvm-project/clang/lib/Lex/PPMacroExpansion.cpp

Line 208 in 077e0c1

if (CurSubmoduleState->VisibleModules.isVisible(MM->getOwningModule())) {

Full diff: https://github.com/llvm/llvm-project/pull/130712.diff

1 Files Affected:

(modified) clang/include/clang/Basic/Module.h (+1-1)

diff --git a/clang/include/clang/Basic/Module.h b/clang/include/clang/Basic/Module.h
index 62cc8acf9588b..3d035f0a5f787 100644
--- a/clang/include/clang/Basic/Module.h
+++ b/clang/include/clang/Basic/Module.h
@@ -888,7 +888,7 @@ class VisibleModuleSet {
 
   /// Get the location at which the import of a module was triggered.
   SourceLocation getImportLoc(const Module *M) const {
-    return M->getVisibilityID() < ImportLocs.size()
+    return M && M->getVisibilityID() < ImportLocs.size()
                ? ImportLocs[M->getVisibilityID()]
                : SourceLocation();
   }

ChuanqiXu9

The patch itself seems not bad. But we prefer to ask for a test for such changes.

shafik

This needs a release note and it would be helpful to know how you found this and a test w/ a minimal reproducer. Are there any bugs reports for this?

matts1 · 2025-03-12T23:21:15Z

There is a bug report on the chromium bug tracker - http://crbug.com/400353616

matts1 · 2025-03-13T06:15:43Z

I have a repro, but it may be addressing the symptoms rather than the root cause.

AFAICT, a ModuleMacro should always have an associated module.

The root cause of the issue appears to be that in the example I provided with the test case, the ModuleMacro constructor is called with OwningModule set to null. I'm not familiar enough with the code, however, to say if that's working as intended. I'm hoping someone more knowledgable than me could answer that.

llvm-project/clang/include/clang/Lex/MacroInfo.h

Line 532 in 6abe19a

ModuleMacro(Module *OwningModule, const IdentifierInfo *II, MacroInfo *Macro,

I'm happy to submit this as is, since a header guard can't hurt, but it may just hide the problem.

clang/test/Modules/pr130712.cppm

atetubou · 2025-03-13T06:37:43Z

clang/test/Modules/pr130712.cppm

+// 1) There must be a configuration mismatch between a header and a file it depends on
+// 2) -fmodules-local-submodule-visibility must be enabled.
+
+// Unfortunately, libcxx is compiled with exceptions, but the sysroot it depends on is likely compiled without exceptions.


Why libcxx is relevant here while any code in this test doesn't include STL header?

You can reproduce this with libcxx, but this is a minimal repro.

The comment is not relevant to the test; can you remove it?

cor3ntin

This change needs a release note.
Please add an entry to clang/docs/ReleaseNotes.rst in the section the most adapted to the change, and referencing any Github issue this change fixes. Thanks!

cor3ntin · 2025-03-14T07:49:05Z

clang/test/Modules/pr130712.cppm

+// 1) There must be a configuration mismatch between a header and a file it depends on
+// 2) -fmodules-local-submodule-visibility must be enabled.
+
+// Unfortunately, libcxx is compiled with exceptions, but the sysroot it depends on is likely compiled without exceptions.


The comment is not relevant to the test; can you remove it?

clang/docs/ReleaseNotes.rst

clang/test/Modules/pr130712.cppm

cor3ntin

LGTM

matts1 · 2025-05-15T01:13:28Z

I've rebased to fix the merge conflicts in the release notes, should be ready to merge.

github-actions · 2025-05-15T02:51:04Z

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If `MM->getOwningModule` returns nullptr, then `isVisible` is called with nullptr, which then calls `getImportLoc(nullptr)` https://github.com/llvm/llvm-project/blob/077e0c134a31cc16c432ce685458b1de80bfbf84/clang/lib/Lex/PPMacroExpansion.cpp#L208

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" clang:modules C++20 modules and Clang Header Modules labels Mar 11, 2025

ChuanqiXu9 reviewed Mar 11, 2025

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shafik reviewed Mar 12, 2025

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matts1 force-pushed the push-qwyquzltunws branch from 4b41cf9 to cf5684b Compare March 13, 2025 06:02

ChuanqiXu9 approved these changes Mar 13, 2025

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atetubou reviewed Mar 13, 2025

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matts1 force-pushed the push-qwyquzltunws branch from cf5684b to 9d29127 Compare March 13, 2025 23:08

cor3ntin reviewed Mar 14, 2025

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matts1 force-pushed the push-qwyquzltunws branch from 76fc1c9 to 2c0dc1e Compare March 17, 2025 06:19

atetubou reviewed Mar 18, 2025

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matts1 force-pushed the push-qwyquzltunws branch from a249bae to 195055e Compare April 15, 2025 02:12

cor3ntin approved these changes May 14, 2025

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[clang] Fix a segfault when M is a nullptr

88512cc

matts1 force-pushed the push-qwyquzltunws branch from 195055e to 88512cc Compare May 15, 2025 01:12

matts1 requested a review from cor3ntin May 15, 2025 01:12

ChuanqiXu9 approved these changes May 15, 2025

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ChuanqiXu9 merged commit 4630d46 into llvm:main May 15, 2025
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matts1 deleted the push-qwyquzltunws branch May 15, 2025 02:53

[clang] Fix a segfault when M is a nullptr #130712

[clang] Fix a segfault when M is a nullptr #130712

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