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Features

ROSE compiler can use Clang as frontend instead of EDG. With this replacement, we can take the advantage of OpenMP support in Clang/LLVM and remove the dependency of proprietary EDG. However, the Clang support in ROSE compiler is still at the early stage. There could be many Clang IRs that it’s unable to recognize, which leads to a compilation failure. In this tutorial we will cover how to support a new Clang IR in ROSE compiler. The goal of this tutorial is to compile a hello-world program successfully.

The following example is the hello-world program used in this tutorial.

cat << EOF > hello-world.c
#include <stdio.h>
int main() {
   printf("Hello World from C\n");
   return 0;
}
EOF

Check the create source code and you should see the same content as above.

cat hello-world.c

Clang IR - `clang::Decl::Var`

By default, ROSE compiler with Clang frontend can’t compile this example due to unsupported Clang IR. While traversing the Clang AST, ROSE will encounter an unknown Clang IR node and can’t continue.

rose-compiler hello-world.c -o hello-world

The following error will be thrown by ROSE.

...
Traverse(clang::Decl : 0x21130f0 : _IO_FILE_plus)  visit done : node = 0x7fea7e2628e8
Unknown declacaration kind: Var !
rose-compiler: /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-decl.cpp:317: virtual SgNode *ClangToSageTranslator::Traverse(clang::Decl *): Assertion `false' failed.
Aborted (core dumped)

The unknown Var declaration refers to clang::Decl::Var. After checking the specified line 317 in clang-frontend-decl.cpp. We can it is a switch-case statement and this unknown Clang IR falls to the default case that indicates an error. Therefore, a handler has to be added in the switch-case statement to tell ROSE how to deal with this Clang IR.

To do that, we insert the following code right above the default case at line 315 in that statement.

case clang::Decl::Var:
    ret_status = VisitVarDecl((clang::VarDecl *)decl, &result);
    break;

vim /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-decl.cpp +315

Clang IR - `clang::Stmt::CallExprClass`

After making the modification, we can recompile ROSE to see whether it works now.

cd $ROSE_BUILD
make core -j4
make install-core
cd ~
rose-compiler hello-world.c -o hello-world

The compilation still failed and ROSE complains that another Clang IR is unknown.

...
ClangToSageTranslator::VisitCompoundStmt
Unknown statement kind: CallExpr !
rose-compiler: /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-stmt.cpp:489: virtual SgNode *ClangToSageTranslator::Traverse(clang::Stmt *): Assertion `false' failed.
Aborted (core dumped)

In the file mentioned in error information, we can find out that it’s a smilar situation, which is the switch statement doesn’t have a valid case for this Clang IR. Therefore, we need to add the corresponding case section as follows.

case clang::Stmt::CallExprClass:
    ret_status = VisitCallExpr((clang::CallExpr *)stmt, &result);
    break;

vim /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-stmt.cpp +486

Clang IR - `clang::ValueStmt`

Again, we need to recompiler ROSE to see the result.

cd $ROSE_BUILD
make core -j4
make install-core
cd ~
rose-compiler hello-world.c -o hello-world

The compilation still failed and a new unknown Clang IR appears.

...
ClangToSageTranslator::VisitCallExpr
ClangToSageTranslator::VisitImplicitCastExpr
ClangToSageTranslator::VisitDeclRefExpr
Lookup symbol for: "printf"
ClangToSageTranslator::VisitFunctionProtoType
ClangToSageTranslator::VisitType
ClangToSageTranslator::VisitExpr
ClangToSageTranslator::VisitValueStmt
rose-compiler: /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-stmt.cpp:1488: virtual bool ClangToSageTranslator::VisitValueStmt(clang::ValueStmt *, SgNode **): Assertion `FAIL_TODO == 0' failed.
Aborted (core dumped)

At the specified line 1488 of file clang-frontend-stmt.cpp, we can see that it’s an unconditional failure, which we can remove for now by deleting this particular line.

ROSE_ASSERT(FAIL_TODO == 0); // TODO

vim /home/freecc/source/rose_src/src/frontend/CxxFrontend/Clang/clang-frontend-stmt.cpp +1488

Result

Now let’s compile ROSE the third time.

cd $ROSE_BUILD
make core -j4
make install-core
cd ~
rose-compiler hello-world.c -o hello-world

Finally! We successfully build both ROSE and the hello-world program! Under current folder, an executable named hello-world and a generated source file will be shown.

ls hello-world
ls rose_hello-world.c

Running hello-world will print a message Hello World from C.

./hello-world

Check the generated rose_hello-world.c and it should display the same content as the original hello-world.c except minor format difference.

cat rose_hello-world.c

Congratulations you were successfully able to support a new Clang IR in ROSE compiler.

Tips:

Features

Clang IR - clang::Decl::Var

Clang IR - clang::Stmt::CallExprClass

Clang IR - clang::ValueStmt

Result

Clang IR - `clang::Decl::Var`

Clang IR - `clang::Stmt::CallExprClass`

Clang IR - `clang::ValueStmt`