Add support for varadic extern "c" functions like printf

Varadic functions are only allowed in extern functions as far as I know.

gcc/rust/backend/rust-compile-context.h

@@ -371,9 +371,14 @@ class TyTyResolveCompile : public TyTy::TyVisitor
 	parameters.push_back (compiled_param);
       }
 
-    translated = ctx->get_backend ()->function_type (
-      receiver, parameters, results, NULL,
-      ctx->get_mappings ()->lookup_location (type.get_ref ()));
+    if (!type.is_varadic ())
+      translated = ctx->get_backend ()->function_type (
+	receiver, parameters, results, NULL,
+	ctx->get_mappings ()->lookup_location (type.get_ref ()));
+    else
+      translated = ctx->get_backend ()->function_type_varadic (
+	receiver, parameters, results, NULL,
+	ctx->get_mappings ()->lookup_location (type.get_ref ()));
   }
 
   void visit (TyTy::FnPtr &type) override

gcc/rust/backend/rust-compile-extern.h

@@ -51,10 +51,8 @@ class CompileExternItem : public HIRCompileBase
     rust_assert (ok);
 
     std::string name = item.get_item_name ();
-
-    // FIXME
-    // this is assuming C ABI
-    std::string asm_name = "_" + name;
+    // FIXME this is assuming C ABI
+    std::string asm_name = name;
 
     Btype *type = TyTyResolveCompile::compile (ctx, resolved_type);
     bool is_external = true;

gcc/rust/backend/rust-compile-tyty.h

@@ -95,9 +95,15 @@ class TyTyCompile : public TyTy::TyVisitor
 	parameters.push_back (compiled_param);
       }
 
-    translated
-      = backend->function_type (receiver, parameters, results, NULL,
-				mappings->lookup_location (type.get_ref ()));
+    if (!type.is_varadic ())
+      translated
+	= backend->function_type (receiver, parameters, results, NULL,
+				  mappings->lookup_location (type.get_ref ()));
+    else
+      translated
+	= backend->function_type_varadic (receiver, parameters, results, NULL,
+					  mappings->lookup_location (
+					    type.get_ref ()));
   }
 
   void visit (TyTy::BoolType &) override

gcc/rust/rust-backend.h

@@ -163,6 +163,13 @@ class Backend
 		 Btype *result_struct, Location location)
     = 0;
 
+  virtual Btype *
+  function_type_varadic (const Btyped_identifier &receiver,
+			 const std::vector<Btyped_identifier> &parameters,
+			 const std::vector<Btyped_identifier> &results,
+			 Btype *result_struct, Location location)
+    = 0;
+
   virtual Btype *function_ptr_type (Btype *result,
 				    const std::vector<Btype *> &praameters,
 				    Location location)

gcc/rust/rust-gcc.cc

@@ -256,6 +256,11 @@ class Gcc_backend : public Backend
 			const std::vector<Btyped_identifier> &, Btype *,
 			const Location);
 
+  Btype *function_type_varadic (const Btyped_identifier &,
+				const std::vector<Btyped_identifier> &,
+				const std::vector<Btyped_identifier> &, Btype *,
+				const Location);
+
   Btype *function_ptr_type (Btype *, const std::vector<Btype *> &, Location);
 
   Btype *struct_type (const std::vector<Btyped_identifier> &);
@@ -1048,6 +1053,62 @@ Gcc_backend::function_type (const Btyped_identifier &receiver,
   return this->make_type (build_pointer_type (fntype));
 }
 
+Btype *
+Gcc_backend::function_type_varadic (
+  const Btyped_identifier &receiver,
+  const std::vector<Btyped_identifier> &parameters,
+  const std::vector<Btyped_identifier> &results, Btype *result_struct, Location)
+{
+  size_t n = parameters.size () + (receiver.btype != NULL ? 1 : 0);
+  tree *args = XALLOCAVEC (tree, n);
+  size_t offs = 0;
+
+  if (receiver.btype != NULL)
+    {
+      tree t = receiver.btype->get_tree ();
+      if (t == error_mark_node)
+	return this->error_type ();
+
+      args[offs++] = t;
+    }
+
+  for (std::vector<Btyped_identifier>::const_iterator p = parameters.begin ();
+       p != parameters.end (); ++p)
+    {
+      tree t = p->btype->get_tree ();
+      if (t == error_mark_node)
+	return this->error_type ();
+      args[offs++] = t;
+    }
+
+  tree result;
+  if (results.empty ())
+    result = void_type_node;
+  else if (results.size () == 1)
+    result = results.front ().btype->get_tree ();
+  else
+    {
+      gcc_assert (result_struct != NULL);
+      result = result_struct->get_tree ();
+    }
+  if (result == error_mark_node)
+    return this->error_type ();
+
+  // The libffi library cannot represent a zero-sized object.  To
+  // avoid causing confusion on 32-bit SPARC, we treat a function that
+  // returns a zero-sized value as returning void.  That should do no
+  // harm since there is no actual value to be returned.  See
+  // https://gcc.gnu.org/PR72814 for details.
+  if (result != void_type_node && int_size_in_bytes (result) == 0)
+    result = void_type_node;
+
+  tree fntype = build_varargs_function_type_array (result, n, args);
+  if (fntype == error_mark_node)
+    return this->error_type ();
+
+  return this->make_type (build_pointer_type (fntype));
+}
+
 Btype *
 Gcc_backend::function_ptr_type (Btype *result_type,
 				const std::vector<Btype *> &parameters,

gcc/rust/typecheck/rust-hir-type-check-implitem.h

@@ -111,11 +111,15 @@ class TypeCheckTopLevelExternItem : public TypeCheckBase
 	context->insert_type (param.get_mappings (), param_tyty);
       }
 
-    auto fnType = new TyTy::FnType (function.get_mappings ().get_hirid (),
-				    function.get_mappings ().get_defid (),
-				    function.get_item_name (),
-				    FNTYPE_IS_EXTERN_FLAG, std::move (params),
-				    ret_type, std::move (substitutions));
+    uint8_t flags = FNTYPE_IS_EXTERN_FLAG;
+    if (function.is_variadic ())
+      flags |= FNTYPE_IS_VARADIC_FLAG;
+
+    auto fnType
+      = new TyTy::FnType (function.get_mappings ().get_hirid (),
+			  function.get_mappings ().get_defid (),
+			  function.get_item_name (), flags, std::move (params),
+			  ret_type, std::move (substitutions));
     context->insert_type (function.get_mappings (), fnType);
   }
 

gcc/rust/typecheck/rust-tyty.cc

@@ -2055,15 +2055,27 @@ TypeCheckCallExpr::visit (FnType &type)
 {
   if (call.num_params () != type.num_params ())
     {
-      rust_error_at (call.get_locus (),
-		     "unexpected number of arguments %lu expected %lu",
-		     call.num_params (), type.num_params ());
-      return;
+      if (type.is_varadic ())
+	{
+	  if (call.num_params () < type.num_params ())
+	    {
+	      rust_error_at (call.get_locus (),
+			     "unexpected number of arguments %lu expected %lu",
+			     call.num_params (), type.num_params ());
+	      return;
+	    }
+	}
+      else
+	{
+	  rust_error_at (call.get_locus (),
+			 "unexpected number of arguments %lu expected %lu",
+			 call.num_params (), type.num_params ());
+	  return;
+	}
     }
 
   size_t i = 0;
   call.iterate_params ([&] (HIR::Expr *param) mutable -> bool {
-    auto fnparam = type.param_at (i);
     auto argument_expr_tyty = Resolver::TypeCheckExpr::Resolve (param, false);
     if (argument_expr_tyty == nullptr)
       {
@@ -2072,12 +2084,19 @@ TypeCheckCallExpr::visit (FnType &type)
 	return false;
       }
 
-    auto resolved_argument_type = fnparam.second->unify (argument_expr_tyty);
-    if (resolved_argument_type == nullptr)
+    auto resolved_argument_type = argument_expr_tyty;
+
+    // it might be a varadic function
+    if (i < type.num_params ())
       {
-	rust_error_at (param->get_locus_slow (),
-		       "Type Resolution failure on parameter");
-	return false;
+	auto fnparam = type.param_at (i);
+	resolved_argument_type = fnparam.second->unify (argument_expr_tyty);
+	if (resolved_argument_type == nullptr)
+	  {
+	    rust_error_at (param->get_locus_slow (),
+			   "Type Resolution failure on parameter");
+	    return false;
+	  }
       }
 
     context->insert_type (param->get_mappings (), resolved_argument_type);
@@ -2086,7 +2105,7 @@ TypeCheckCallExpr::visit (FnType &type)
     return true;
   });
 
-  if (i != call.num_params ())
+  if (i < call.num_params ())
     {
       rust_error_at (call.get_locus (),
 		     "unexpected number of arguments %lu expected %lu", i,

gcc/rust/typecheck/rust-tyty.h

@@ -973,6 +973,7 @@ class FnType : public BaseType, public SubstitutionRef
 #define FNTYPE_DEFAULT_FLAGS 0x00
 #define FNTYPE_IS_METHOD_FLAG 0x01
 #define FNTYPE_IS_EXTERN_FLAG 0x02
+#define FNTYPE_IS_VARADIC_FLAG 0X04
 
   FnType (HirId ref, DefId id, std::string identifier, uint8_t flags,
 	  std::vector<std::pair<HIR::Pattern *, BaseType *> > params,
@@ -1031,6 +1032,8 @@ class FnType : public BaseType, public SubstitutionRef
 
   bool is_extern () const { return (flags & FNTYPE_IS_EXTERN_FLAG) != 0; }
 
+  bool is_varadic () const { return (flags & FNTYPE_IS_VARADIC_FLAG) != 0; }
+
   DefId get_id () const { return id; }
 
   // get the Self type for the method

gcc/testsuite/rust/execute/torture/helloworld2.rs

@@ -0,0 +1,15 @@
+/* { dg-output "Hello World 123\n" }*/
+extern "C" {
+    fn printf(s: *const i8, ...);
+}
+
+fn main() -> i32 {
+    unsafe {
+        let a = "Hello World %i\n";
+        let b = a as *const str;
+        let c = b as *const i8;
+
+        printf(c, 123);
+    }
+    0
+}