[PATCH] D54344: [Clang][CodeGen][CXX]: Workaround __attribute((no_destroy)) crash/incorrect code generation.

[Kristina Brooks via Phabricator via cfe-commits]

kristina updated this revision to Diff 173530.
kristina set the repository for this revision to rC Clang.
kristina added a comment.

@erik.pilkington Fantastic catch, I totally forgot about the global flag. Revised, moved to CodeGenCXX, added a test to verify ctor/dtor is balanced under normal circumstances and two tests to ensure ctor is not balanced with either flag or attribute.

  => ninja check-clang-codegencxx
  
  Testing Time: 7.68s
    Expected Passes    : 927
    Expected Failures  : 2
    Unsupported Tests  : 5

The attribute was actually missing tests for IR generation so thank you for suggesting moving them there, I think this covers all cases for this bug (balanced regression test without attr or flag, unbalanced test because of attr, unbalanced test because of global flag).


Repository:
  rC Clang

https://reviews.llvm.org/D54344

Files:
  lib/CodeGen/CGDeclCXX.cpp
  test/CodeGenCXX/attr-no-destroy-d54344.cpp


Index: test/CodeGenCXX/attr-no-destroy-d54344.cpp
===================================================================
--- test/CodeGenCXX/attr-no-destroy-d54344.cpp
+++ test/CodeGenCXX/attr-no-destroy-d54344.cpp
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR  %s -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu %s -o - | FileCheck %s --check-prefix=CHECK-ATTR
+// RUN: %clang_cc1 -std=c++2a -emit-llvm -O0 -triple x86_64-unknown-linux-gnu -DNOATTR -fno-c++-static-destructors %s -o - | FileCheck %s --check-prefix=CHECK-FLAG 
+// REQUIRES: asserts
+
+// Regression test for D54344. Class with no user-defined destructor
+// that has an inherited member that has a non-trivial destructor
+// and a non-default constructor will attempt to emit a destructor
+// despite being marked as __attribute((no_destroy)) in which case
+// it would trigger an assertion due to an incorrect assumption.
+// This test requires asserts to reliably work as without the crash
+// it generates working but semantically incorrect code.
+
+class a {
+public:
+  ~a();
+};
+class logger_base {
+  a d;
+};
+class e : logger_base {};
+#ifndef NOATTR
+__attribute((no_destroy))
+#endif
+e g;
+
+// In the absence of the attribute and flag, both ctor and dtor should
+// be emitted, check for that.
+// CHECK: @__cxx_global_var_init
+// CHECK: @__cxa_atexit
+
+// When attribute is enabled, the constructor should not be balanced
+// by a destructor. Make sure we have the ctor but not the dtor
+// registration.
+// CHECK-ATTR: @__cxx_global_var_init
+// CHECK-ATTR-NOT: @__cxa_atexit
+
+// Same scenario except with global flag (-fno-c++-static-destructors)
+// supressing it instead of the attribute. 
+// CHECK-FLAG: @__cxx_global_var_init
+// CHECK-FLAG-NOT: @__cxa_atexit
Index: lib/CodeGen/CGDeclCXX.cpp
===================================================================
--- lib/CodeGen/CGDeclCXX.cpp
+++ lib/CodeGen/CGDeclCXX.cpp
@@ -64,6 +64,15 @@
 /// static storage duration.
 static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
                             ConstantAddress Addr) {
+  // Honor __attribute__((no_destroy)) and bail instead of attempting
+  // to emit a reference to a possibly non-existant destructor, which
+  // in turn can cause a crash. This will result in a global constructor
+  // that isn't balanced out by a destructor call as intended by the
+  // attribute. This also checks for -fno-c++-static-destructors and
+  // bails even if the attribute is not present. (D54344)
+  if (D.isNoDestroy(CGF.getContext()))
+    return;
+  
   CodeGenModule &CGM = CGF.CGM;
 
   // FIXME:  __attribute__((cleanup)) ?


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