[clang] [Clang] fix crash by avoiding invalidation of extern main declaration during strictness checks (PR #104594)

[Oleksandr T. via cfe-commits]

https://github.com/a-tarasyuk updated https://github.com/llvm/llvm-project/pull/104594

>From 9ffe47795d3fa25d6ac020b5cebace0c2e758285 Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Fri, 16 Aug 2024 17:21:38 +0300
Subject: [PATCH 1/4] [Clang] fix crash by avoiding invalidation of extern main
 declaration during strictness checks

---
 clang/docs/ReleaseNotes.rst                   |  1 +
 clang/lib/Sema/SemaDecl.cpp                   |  1 -
 .../basic/basic.start/basic.start.main/p3.cpp | 31 ++++++++++++++-----
 3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ffdd063ec99037..1731100fdbcf87 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -264,6 +264,7 @@ Bug Fixes to C++ Support
 - Properly reject defaulted copy/move assignment operators that have a non-reference explicit object parameter.
 - Clang now properly handles the order of attributes in `extern` blocks. (#GH101990).
 - Fixed an assertion failure by preventing null explicit object arguments from being deduced. (#GH102025).
+- Fixed a crash caused by marking the function declaration as invalid during strictness checks on ``extern`` main. (#GH104570).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d19a16cf2ba150..5bba9c1750287d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12233,7 +12233,6 @@ void Sema::CheckMain(FunctionDecl *FD, const DeclSpec &DS) {
        FD->getDeclContext()->getRedeclContext()->isTranslationUnit())) {
     Diag(FD->getLocation(), diag::ext_main_invalid_linkage_specification)
         << FD->getLanguageLinkage();
-    FD->setInvalidDecl();
     return;
   }
 
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index d23d00ccdeebc1..0d2c5fbb37afe7 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -11,6 +11,8 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST11
 // RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST12
 // RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST13
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST14
+// RUN: %clang_cc1 -triple x86_64-linux -emit-llvm-only -verify -pedantic %s -DTEST15
 
 #if TEST1
 int main; // expected-error{{main cannot be declared as a variable in the global scope}}
@@ -78,12 +80,12 @@ namespace ns {
 extern "C" struct A { int main(); }; // ok
 
 namespace c {
-  extern "C" void main(); // expected-warning {{'main' should not be 'extern "C"'}}
+  extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
 }
 
 extern "C" {
   namespace Z {
-    void main(); // expected-warning {{'main' should not be 'extern "C"'}}
+    int main(); // expected-warning {{'main' should not be 'extern "C"'}}
   }
 }
 
@@ -102,11 +104,6 @@ extern "C++" {
   int main(); // expected-warning {{'main' should not be 'extern "C++"'}}
 }
 
-extern "C" {
-  int main(); // expected-warning {{'main' should not be 'extern "C"'}}
-}
-
-extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
 extern "C++" int main(); // expected-warning {{'main' should not be 'extern "C++"'}}
 
 namespace ns1 {
@@ -122,6 +119,26 @@ namespace ns2 {
   extern "C++" void main() {} // ok
 }
 
+#elif TEST14
+extern "C" {
+  int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+}
+
+extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+
+#elif TEST15
+extern "C" __attribute__((visibility("default"))) __attribute__((weak))
+int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+
+using uptr = unsigned long;
+
+extern bool f(uptr, uptr);
+bool InitModuleList() {
+  uptr me = reinterpret_cast<uptr>(InitModuleList);
+  uptr exe = reinterpret_cast<uptr>(&main); // expected-warning {{referring to 'main' within an expression is a Clang extension}}
+  return f(me, exe);
+}
+
 #else
 #error Unknown Test
 #endif

>From 0ea146acc97e2761b401cca5f9b664d39d2a0e9f Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Fri, 16 Aug 2024 18:08:40 +0300
Subject: [PATCH 2/4] cleanup

---
 clang/docs/ReleaseNotes.rst | 1 -
 clang/lib/Sema/SemaDecl.cpp | 4 +---
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1731100fdbcf87..ffdd063ec99037 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -264,7 +264,6 @@ Bug Fixes to C++ Support
 - Properly reject defaulted copy/move assignment operators that have a non-reference explicit object parameter.
 - Clang now properly handles the order of attributes in `extern` blocks. (#GH101990).
 - Fixed an assertion failure by preventing null explicit object arguments from being deduced. (#GH102025).
-- Fixed a crash caused by marking the function declaration as invalid during strictness checks on ``extern`` main. (#GH104570).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 5bba9c1750287d..1d85341bc9a8b6 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12230,11 +12230,9 @@ void Sema::CheckMain(FunctionDecl *FD, const DeclSpec &DS) {
   //    The main function shall not be declared with a linkage-specification.
   if (FD->isExternCContext() ||
       (FD->isExternCXXContext() &&
-       FD->getDeclContext()->getRedeclContext()->isTranslationUnit())) {
+       FD->getDeclContext()->getRedeclContext()->isTranslationUnit()))
     Diag(FD->getLocation(), diag::ext_main_invalid_linkage_specification)
         << FD->getLanguageLinkage();
-    return;
-  }
 
   // C++11 [basic.start.main]p3:
   //   A program that [...] declares main to be inline, static or

>From 4ca14697ca76c4248858f4a7b0a08c8768b18062 Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Fri, 16 Aug 2024 18:21:39 +0300
Subject: [PATCH 3/4] simplify test

---
 clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index 0d2c5fbb37afe7..67be6c16ef9333 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -130,13 +130,8 @@ extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
 extern "C" __attribute__((visibility("default"))) __attribute__((weak))
 int main(); // expected-warning {{'main' should not be 'extern "C"'}}
 
-using uptr = unsigned long;
-
-extern bool f(uptr, uptr);
-bool InitModuleList() {
-  uptr me = reinterpret_cast<uptr>(InitModuleList);
-  uptr exe = reinterpret_cast<uptr>(&main); // expected-warning {{referring to 'main' within an expression is a Clang extension}}
-  return f(me, exe);
+unsigned long g() {
+  return reinterpret_cast<unsigned long>(&main); // expected-warning {{referring to 'main' within an expression is a Clang extension}}
 }
 
 #else

>From 3234a798ee2a0bb468b4521b19080060dab06730 Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Fri, 16 Aug 2024 21:10:20 +0300
Subject: [PATCH 4/4] test void main functions

---
 clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index 67be6c16ef9333..497a9328c11561 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -80,12 +80,14 @@ namespace ns {
 extern "C" struct A { int main(); }; // ok
 
 namespace c {
-  extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+  extern "C" void main(); // expected-error {{'main' must return 'int'}} \
+                          // expected-warning {{'main' should not be 'extern "C"'}}
 }
 
 extern "C" {
   namespace Z {
-    int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+    void main(); // expected-error {{'main' must return 'int'}} \
+                 // expected-warning {{'main' should not be 'extern "C"'}}
   }
 }