https://github.com/a-tarasyuk updated
https://github.com/llvm/llvm-project/pull/101853
>From 3f8050482f54138c8a836e67e45131d5e9ccf5cc 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/include/clang/AST/DeclBase.h | 2 +
.../clang/Basic/DiagnosticSemaKinds.td | 2 +
clang/include/clang/Sema/Sema.h | 3 +-
clang/lib/AST/Decl.cpp | 8 ++--
clang/lib/Sema/SemaDecl.cpp | 42 ++++++++++++++-----
clang/test/SemaCXX/linkage1.cpp | 22 ++++++++++
clang/test/SemaCXX/linkage3.cpp | 5 +++
8 files changed, 69 insertions(+), 17 deletions(-)
create mode 100644 clang/test/SemaCXX/linkage1.cpp
create mode 100644 clang/test/SemaCXX/linkage3.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/AST/DeclBase.h
b/clang/include/clang/AST/DeclBase.h
index 40f01abf384e9..e28626eabe8e8 100644
--- a/clang/include/clang/AST/DeclBase.h
+++ b/clang/include/clang/AST/DeclBase.h
@@ -2156,6 +2156,8 @@ class DeclContext {
return getDeclKind() == Decl::TranslationUnit;
}
+ bool isLinkageSpec() const { return getDeclKind() == Decl::LinkageSpec; }
+
bool isRecord() const {
return getDeclKind() >= Decl::firstRecord &&
getDeclKind() <= Decl::lastRecord;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 581434d33c5c9..e86b391264d2a 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -990,6 +990,8 @@ 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_main_invalid_linkage_specification : ExtWarn<
+ "'main' cannot have linkage specification 'extern \"C\"'">, InGroup<Main>;
/// 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..d791991fcfd8b 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -3585,8 +3585,9 @@ 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);
+ bool CheckLinkageSpecification(DeclContext *DC, Decl *D);
/// Returns an implicit CodeSegAttr if a __declspec(code_seg) is found on a
/// containing class. Otherwise it will return implicit SectionAttr if the
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 490c4a2fc525c..aa2ad1752cc5c 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -3292,11 +3292,9 @@ 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 DeclContext *DC = getDeclContext();
+ return isNamed(this, "main") && !getLangOpts().Freestanding &&
+ (DC->getRedeclContext()->isTranslationUnit() || DC->isLinkageSpec());
}
bool FunctionDecl::isMSVCRTEntryPoint() const {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 4fea38d1b02a9..832082d547bf4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7353,6 +7353,15 @@ void emitReadOnlyPlacementAttrWarning(Sema &S, const
VarDecl *VD) {
}
}
+static bool isMainVar(DeclarationName Name, VarDecl *VD) {
+ if (Name.getAsIdentifierInfo() && Name.getAsIdentifierInfo()->isStr("main")
&&
+ !VD->getDescribedVarTemplate()) {
+ const DeclContext *DC = VD->getDeclContext();
+ return DC->getRedeclContext()->isTranslationUnit() || DC->isLinkageSpec();
+ }
+ return false;
+}
+
NamedDecl *Sema::ActOnVariableDeclarator(
Scope *S, Declarator &D, DeclContext *DC, TypeSourceInfo *TInfo,
LookupResult &Previous, MultiTemplateParamsArg TemplateParamLists,
@@ -8052,15 +8061,13 @@ NamedDecl *Sema::ActOnVariableDeclarator(
}
// Special handling of variable named 'main'.
- if (Name.getAsIdentifierInfo() && Name.getAsIdentifierInfo()->isStr("main")
&&
- NewVD->getDeclContext()->getRedeclContext()->isTranslationUnit() &&
- !getLangOpts().Freestanding && !NewVD->getDescribedVarTemplate()) {
-
+ if (isMainVar(Name, NewVD) && !getLangOpts().Freestanding) {
// C++ [basic.start.main]p3
// A program that declares a variable main at global scope is ill-formed.
- if (getLangOpts().CPlusPlus)
- Diag(D.getBeginLoc(), diag::err_main_global_variable);
-
+ if (getLangOpts().CPlusPlus) {
+ if (!CheckLinkageSpecification(DC, NewVD))
+ Diag(D.getBeginLoc(), diag::err_main_global_variable);
+ }
// In C, and external-linkage variable named main results in undefined
// behavior.
else if (NewVD->hasExternalFormalLinkage())
@@ -10308,7 +10315,7 @@ 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 +10480,7 @@ 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 +12217,10 @@ 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) {
+ if (CheckLinkageSpecification(DC, FD))
+ return;
+
// C++11 [basic.start.main]p3:
// A program that [...] declares main to be inline, static or
// constexpr is ill-formed.
@@ -12238,7 +12248,6 @@ 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>();
@@ -12370,6 +12379,17 @@ void Sema::CheckMain(FunctionDecl* FD, const DeclSpec&
DS) {
}
}
+bool Sema::CheckLinkageSpecification(DeclContext *DC, Decl *D) {
+ // [basic.start.main] p2
+ // The main function shall not be declared with a linkage-specification.
+ if (DC->isExternCContext()) {
+ Diag(D->getLocation(), diag::err_main_invalid_linkage_specification);
+ D->setInvalidDecl();
+ return true;
+ }
+ return false;
+}
+
static bool isDefaultStdCall(FunctionDecl *FD, Sema &S) {
// Default calling convention for main and wmain is __cdecl
diff --git a/clang/test/SemaCXX/linkage1.cpp b/clang/test/SemaCXX/linkage1.cpp
new file mode 100644
index 0000000000000..3446e85af44be
--- /dev/null
+++ b/clang/test/SemaCXX/linkage1.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s
+
+namespace c {
+ extern "C" void main(); // expected-error {{'main' cannot have linkage
specification 'extern "C"'}}
+}
+extern "C" {
+ int main(); // expected-error {{'main' cannot have linkage specification
'extern "C"'}}
+}
+
+extern "C" int main(); // expected-error {{'main' cannot have linkage
specification 'extern "C"'}}
+extern "C" struct A { int main(); }; // ok
+
+namespace ns {
+ extern "C" int main; // expected-error {{'main' cannot have linkage
specification 'extern "C"'}}
+ extern "C" struct A {
+ int main; // ok
+ };
+
+ extern "C" struct B {
+ int main(); // ok
+ };
+}
diff --git a/clang/test/SemaCXX/linkage3.cpp b/clang/test/SemaCXX/linkage3.cpp
new file mode 100644
index 0000000000000..f80d76121d4af
--- /dev/null
+++ b/clang/test/SemaCXX/linkage3.cpp
@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s
+
+extern "C" {
+ void* main; // expected-error {{'main' cannot have linkage specification
'extern "C"'}}
+}
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