https://github.com/a-tarasyuk updated
https://github.com/llvm/llvm-project/pull/101853
>From f4f091b742d7b7ca0a96725b42a7cd09530240f5 Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.taras...@outlook.com>
Date: Sun, 4 Aug 2024 00:45:49 +0300
Subject: [PATCH] [Clang] strengthen checks for 'main' function to meet
[basic.start.main] p2 requirements
---
clang/docs/ReleaseNotes.rst | 2 ++
.../clang/Basic/DiagnosticSemaKinds.td | 3 ++
clang/include/clang/Sema/Sema.h | 2 +-
clang/lib/AST/Decl.cpp | 14 +++++----
clang/lib/Sema/SemaDecl.cpp | 15 +++++++---
clang/test/SemaCXX/linkage1.cpp | 29 +++++++++++++++++++
6 files changed, 55 insertions(+), 10 deletions(-)
create mode 100644 clang/test/SemaCXX/linkage1.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4c7bd099420ab..3303db5a87ace 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -145,6 +145,8 @@ Improvements to Clang's diagnostics
- -Wdangling-assignment-gsl is enabled by default.
+- Clang now diagnoses the use of `main` in `extern` context as invalid
according to [basic.start.main] p2. Fixes #GH101512.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 581434d33c5c9..2005133b2f568 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -990,6 +990,9 @@ def warn_main_redefined : Warning<"variable named 'main'
with external linkage "
"has undefined behavior">, InGroup<Main>;
def ext_main_used : Extension<
"referring to 'main' within an expression is a Clang extension">,
InGroup<Main>;
+def err_invalid_linkage_specification : Extension<
+ "invalid linkage specification "
+ "'extern \"%select{C|C++}0\"'">;
/// parser diagnostics
def ext_no_declarators : ExtWarn<"declaration does not declare anything">,
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 2ec6367eccea0..0fc07d4a01ad3 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -3585,7 +3585,7 @@ class Sema final : public SemaBase {
/// \param OldT The portion of the type of the old declaration to check.
bool canFullyTypeCheckRedeclaration(ValueDecl *NewD, ValueDecl *OldD,
QualType NewT, QualType OldT);
- void CheckMain(FunctionDecl *FD, const DeclSpec &D);
+ void CheckMain(FunctionDecl *FD, DeclContext *DC, const DeclSpec &D);
void CheckMSVCRTEntryPoint(FunctionDecl *FD);
/// Returns an implicit CodeSegAttr if a __declspec(code_seg) is found on a
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 490c4a2fc525c..447297103f396 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -3292,11 +3292,15 @@ bool FunctionDecl::isImmediateFunction() const {
}
bool FunctionDecl::isMain() const {
- const TranslationUnitDecl *tunit =
- dyn_cast<TranslationUnitDecl>(getDeclContext()->getRedeclContext());
- return tunit &&
- !tunit->getASTContext().getLangOpts().Freestanding &&
- isNamed(this, "main");
+ const TranslationUnitDecl *TUnit =
+ dyn_cast<TranslationUnitDecl>(getDeclContext()->getRedeclContext());
+ const LinkageSpecDecl *LSD = dyn_cast<LinkageSpecDecl>(getDeclContext());
+ if (!TUnit && !LSD)
+ return false;
+ if ((TUnit && TUnit->getASTContext().getLangOpts().Freestanding) ||
+ (LSD && LSD->getASTContext().getLangOpts().Freestanding))
+ return false;
+ return isNamed(this, "main");
}
bool FunctionDecl::isMSVCRTEntryPoint() const {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 4fea38d1b02a9..ae6d6681d6029 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -10308,7 +10308,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D,
DeclContext *DC,
if (!getLangOpts().CPlusPlus) {
// Perform semantic checking on the function declaration.
if (!NewFD->isInvalidDecl() && NewFD->isMain())
- CheckMain(NewFD, D.getDeclSpec());
+ CheckMain(NewFD, DC, D.getDeclSpec());
if (!NewFD->isInvalidDecl() && NewFD->isMSVCRTEntryPoint())
CheckMSVCRTEntryPoint(NewFD);
@@ -10473,7 +10473,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D,
DeclContext *DC,
// Perform semantic checking on the function declaration.
if (!NewFD->isInvalidDecl() && NewFD->isMain())
- CheckMain(NewFD, D.getDeclSpec());
+ CheckMain(NewFD, DC, D.getDeclSpec());
if (!NewFD->isInvalidDecl() && NewFD->isMSVCRTEntryPoint())
CheckMSVCRTEntryPoint(NewFD);
@@ -12210,7 +12210,15 @@ bool Sema::CheckFunctionDeclaration(Scope *S,
FunctionDecl *NewFD,
return Redeclaration;
}
-void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
+void Sema::CheckMain(FunctionDecl *FD, DeclContext *DC, const DeclSpec &DS) {
+ // [basic.start.main] p2
+ // The main function shall not be declared with a linkage-specification.
+ if (DC->isExternCXXContext() || DC->isExternCContext()) {
+ Diag(FD->getLocation(), diag::err_invalid_linkage_specification)
+ << FD->getLanguageLinkage();
+ FD->setInvalidDecl();
+ return;
+ }
// C++11 [basic.start.main]p3:
// A program that [...] declares main to be inline, static or
// constexpr is ill-formed.
@@ -12238,7 +12246,6 @@ void Sema::CheckMain(FunctionDecl* FD, const DeclSpec&
DS) {
<< FixItHint::CreateRemoval(DS.getConstexprSpecLoc());
FD->setConstexprKind(ConstexprSpecKind::Unspecified);
}
-
if (getLangOpts().OpenCL) {
Diag(FD->getLocation(), diag::err_opencl_no_main)
<< FD->hasAttr<OpenCLKernelAttr>();
diff --git a/clang/test/SemaCXX/linkage1.cpp b/clang/test/SemaCXX/linkage1.cpp
new file mode 100644
index 0000000000000..8be82209afc08
--- /dev/null
+++ b/clang/test/SemaCXX/linkage1.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s
+
+namespace c {
+ extern "C" void main(); // expected-error {{invalid linkage specification
'extern "C"'}}
+}
+extern "C" {
+ int main(); // expected-error {{invalid linkage specification 'extern "C"'}}
+}
+extern "C" int main(); // expected-error {{invalid linkage specification
'extern "C"'}}
+extern "C" struct A { int main(); }; // ok
+
+namespace cpp {
+ extern "C++" int main(); // expected-error {{invalid linkage specification
'extern "C++"'}}
+}
+extern "C++" {
+ int main(); // expected-error {{invalid linkage specification 'extern
"C++"'}}
+}
+extern "C++" int main(); // expected-error {{invalid linkage specification
'extern "C++"'}}
+extern "C++" struct B { int main(); }; // ok
+
+namespace ns {
+ extern "C" struct A {
+ int main; // ok
+ };
+
+ extern "C" struct B {
+ int main(); // ok
+ };
+}
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