Changeset f1791a4

Timestamp:

Oct 15, 2020, 9:41:31 PM (4 years ago)

Author:

Michael Brooks <mlbrooks@…>

Branches:

ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, master, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

afe2939

Parents:

0b18db7

Message:

Expanding earlier #182 fix to another case of the same issue. Fixes #224?

There is now a reusable helper function addDataSectonAttribute that applies the fix to an ObjectDecl? when we realize it needs it. Test const-init is expanded with case of #224.

Files:

• src/InitTweak/FixGlobalInit.cc (modified) (1 diff)
• src/InitTweak/FixInit.cc (modified) (1 diff)
• src/InitTweak/InitTweak.cc (modified) (1 diff)
• src/InitTweak/InitTweak.h (modified) (1 diff)
• tests/.expect/const-init.txt (modified) (1 diff)
• tests/const-init.cfa (modified) (2 diffs)

src/InitTweak/FixGlobalInit.cc

@@ -112 +112 @@
                         } // if
                         if ( Statement * ctor = ctorInit->ctor ) {
-                                // Translation 1: Add this attribute on the global declaration:
-                                //    __attribute__((section (".data#")))
-                                // which makes gcc put the global in the data section,
-                                // so that the global is writeable (via a const cast) in the init function.
-                                // The trailing # is an injected assembly comment, to suppress the "a" in
-                                //    .section .data,"a"
-                                //    .section .data#,"a"
-                                // to avoid assembler warning "ignoring changed section attributes for .data"
-                                Type *strLitT = new PointerType( Type::Qualifiers( ),
-                                        new BasicType( Type::Qualifiers( ), BasicType::Char ) );
-                                std::list< Expression * > attr_params;
-                                attr_params.push_back( 
-                                        new ConstantExpr( Constant( strLitT, "\".data#\"", std::nullopt ) ) );
-                                objDecl->attributes.push_back(new Attribute("section", attr_params));
-                                // Translation 2: Move the initizliation off the global declaration,
-                                // into the startup function.
+                                addDataSectonAttribute( objDecl );
                                 initStatements.push_back( ctor );
                                 objDecl->init = nullptr;

src/InitTweak/FixInit.cc

@@ -802 +802 @@
                                 if ( Statement * ctor = ctorInit->get_ctor() ) {
                                         if ( objDecl->get_storageClasses().is_static ) {
+
+                                                // The ojbect needs to go in the data section, regardless of dtor complexity below.
+                                                // The attribute works, and is meant to apply, both for leaving the static local alone,
+                                                // and for hoisting it out as a static global.
+                                                addDataSectonAttribute( objDecl );
+
                                                 // originally wanted to take advantage of gcc nested functions, but
                                                 // we get memory errors with this approach. To remedy this, the static

src/InitTweak/InitTweak.cc

@@ -1055 +1055 @@
                 return isCopyFunction( decl, "?{}" );
         }
+
+        void addDataSectonAttribute( ObjectDecl * objDecl ) {
+                Type *strLitT = new PointerType( Type::Qualifiers( ),
+                        new BasicType( Type::Qualifiers( ), BasicType::Char ) );
+                std::list< Expression * > attr_params;
+                attr_params.push_back( 
+                        new ConstantExpr( Constant( strLitT, "\".data#\"", std::nullopt ) ) );
+                objDecl->attributes.push_back(new Attribute("section", attr_params));
+        }
+
 }

src/InitTweak/InitTweak.h

@@ -103 +103 @@
         bool isConstExpr( Initializer * init );
 
+        /// Modifies objDecl to have:
+        ///    __attribute__((section (".data#")))
+        /// which makes gcc put the declared variable in the data section,
+        /// which is helpful for global constants on newer gcc versions,
+        /// so that CFA's generated initialization won't segfault when writing it via a const cast.
+        /// The trailing # is an injected assembly comment, to suppress the "a" in
+        ///    .section .data,"a"
+        ///    .section .data#,"a"
+        /// to avoid assembler warning "ignoring changed section attributes for .data"
+        void addDataSectonAttribute( ObjectDecl * objDecl );
+
         class InitExpander_old {
         public:

tests/.expect/const-init.txt

@@ -1 @@
-done
+almost done
+dtor

tests/const-init.cfa

@@ -16 +16 @@
 /*
 
-This test shows non-crashing of generated code for constants with interesting initizers.
+These tests show non-crashing of generated code for constants with interesting initializers.
 The potential for these to crash is compiler dependent.
 
 There are two cases:
-1. static constants in one compilation unit (tested here)
+1. static constants in one compilation unit (tested here, in a few sub-cases)
 2. extern constants across compilation units (tested by libcfa being loadable, specifically
-   the constant declarations in libcfa/src/limits.cfa, which almost every test exercises,
+   the constant definitions in libcfa/src/limits.cfa, which almost every test exercises,
    including "hello;" but notably, the "limits" test does not exercise it because that test
    is compile-only)
@@ -37 +37 @@
 GCC-10 on Ubuntu 20.04    Has crashed      Has crashed
 
-For this test case to fail, with most other tests passing, would be a situation only ever
+For this test to fail, with most other tests passing, would be a situation only ever
 observed with GCC-8.
 
 */
 
+// initailized by generated function, called before main
 static const char foo = -1;
 
+struct thing{};
+void ^?{}( thing & ) { printf("dtor\n"); }
+
 int main() {
-    printf("done\n");
+    // foo is already initialized
+
+    // no dtor => stays a (static) local, initialized here
+    static const char bar = -1;
+
+    // has dtor => becomes a global, ctor called here, dtor called at exit
+    static const thing it;
+
+    printf("almost done\n");
 }