Changeset 6fbe9a5 for src

Timestamp:

Oct 7, 2020, 9:33:22 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:

8e4bc30

Parents:

69c5c00

Message:

Fixing code-gen of constants. Fixes #182? Removes workaround 58b6d1.

Forcing recent GCC versions to place CFA-initialized constants in writeable memory, so CFA initialization doesn't segfault when writing them. See the const-init test for specifics about recent GCC versions.

src/InitTweak/FixGlobalInit.cc: generating the attribute to control GCC's placement
libcfa/src/limits.* : removing workaround from 58b6d1, making these limits const again
tests//limits.* : commenting old test that uses the constants from licfa-limits, explaining what the test doesn't exercise
tests//const-init.* : new test of static constants, taken from #182, and comments explaining how to test this issue

File:

• src/InitTweak/FixGlobalInit.cc (modified) (1 diff)

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.
                                 initStatements.push_back( ctor );
                                 objDecl->init = nullptr;