Merge #1149

1149: backend: handle no_mangle attribute r=philberty a=liushuyu

- handle the `no_mangle` attribute

Co-authored-by: liushuyu <liushuyu011@gmail.com>

gcc/rust/backend/rust-compile-base.cc

@@ -26,14 +26,21 @@
 
 #include "fold-const.h"
 #include "stringpool.h"
+#include "attribs.h"
 
 namespace Rust {
 namespace Compile {
 
+bool inline should_mangle_item (const tree fndecl)
+{
+  return lookup_attribute ("no_mangle", DECL_ATTRIBUTES (fndecl)) == NULL_TREE;
+}
+
 void
-HIRCompileBase::setup_attributes_on_fndecl (
-  tree fndecl, bool is_main_entry_point, HIR::Visibility &visibility,
-  const HIR::FunctionQualifiers &qualifiers, const AST::AttrVec &attrs)
+HIRCompileBase::setup_fndecl (tree fndecl, bool is_main_entry_point,
+			      HIR::Visibility &visibility,
+			      const HIR::FunctionQualifiers &qualifiers,
+			      const AST::AttrVec &attrs)
 {
   // if its the main fn or pub visibility mark its as DECL_PUBLIC
   // please see https://github.com/Rust-GCC/gccrs/pull/137
@@ -58,6 +65,7 @@ HIRCompileBase::setup_attributes_on_fndecl (
       bool is_cold = attr.get_path ().as_string ().compare ("cold") == 0;
       bool is_link_section
 	= attr.get_path ().as_string ().compare ("link_section") == 0;
+      bool no_mangle = attr.get_path ().as_string ().compare ("no_mangle") == 0;
       if (is_inline)
 	{
 	  handle_inline_attribute_on_fndecl (fndecl, attr);
@@ -74,6 +82,10 @@ HIRCompileBase::setup_attributes_on_fndecl (
 	{
 	  handle_link_section_attribute_on_fndecl (fndecl, attr);
 	}
+      else if (no_mangle)
+	{
+	  handle_no_mangle_attribute_on_fndecl (fndecl, attr);
+	}
     }
 }
 
@@ -120,6 +132,21 @@ HIRCompileBase::handle_link_section_attribute_on_fndecl (
   set_decl_section_name (fndecl, msg_str.c_str ());
 }
 
+void
+HIRCompileBase::handle_no_mangle_attribute_on_fndecl (
+  tree fndecl, const AST::Attribute &attr)
+{
+  if (attr.has_attr_input ())
+    {
+      rust_error_at (attr.get_locus (),
+		     "attribute %<no_mangle%> does not accept any arguments");
+      return;
+    }
+
+  DECL_ATTRIBUTES (fndecl) = tree_cons (get_identifier ("no_mangle"), NULL_TREE,
+					DECL_ATTRIBUTES (fndecl));
+}
+
 void
 HIRCompileBase::handle_inline_attribute_on_fndecl (tree fndecl,
 						   const AST::Attribute &attr)
@@ -396,16 +423,21 @@ HIRCompileBase::compile_function (
   // we don't mangle the main fn since we haven't implemented the main shim
   bool is_main_fn = fn_name.compare ("main") == 0;
   std::string asm_name = fn_name;
-  if (!is_main_fn)
-    asm_name = ctx->mangle_item (fntype, *canonical_path);
 
   unsigned int flags = 0;
   tree fndecl = ctx->get_backend ()->function (compiled_fn_type, ir_symbol_name,
-					       asm_name, flags, locus);
-  setup_attributes_on_fndecl (fndecl, is_main_fn, visibility, qualifiers,
-			      outer_attrs);
+					       "" /* asm_name */, flags, locus);
+  setup_fndecl (fndecl, is_main_fn, visibility, qualifiers, outer_attrs);
   setup_abi_options (fndecl, fntype->get_abi ());
 
+  // conditionally mangle the function name
+  bool should_mangle = should_mangle_item (fndecl);
+  if (!is_main_fn && should_mangle)
+    asm_name = ctx->mangle_item (fntype, *canonical_path);
+  SET_DECL_ASSEMBLER_NAME (fndecl,
+			   get_identifier_with_length (asm_name.data (),
+						       asm_name.length ()));
+
   // insert into the context
   ctx->insert_function_decl (fntype, fndecl);
 

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

@@ -75,9 +75,10 @@ protected:
   tree resolve_unsized_adjustment (Resolver::Adjustment &adjustment,
 				   tree expression, Location locus);
 
-  static void setup_attributes_on_fndecl (
-    tree fndecl, bool is_main_entry_point, HIR::Visibility &visibility,
-    const HIR::FunctionQualifiers &qualifiers, const AST::AttrVec &attrs);
+  static void setup_fndecl (tree fndecl, bool is_main_entry_point,
+			    HIR::Visibility &visibility,
+			    const HIR::FunctionQualifiers &qualifiers,
+			    const AST::AttrVec &attrs);
 
   static void handle_inline_attribute_on_fndecl (tree fndecl,
 						 const AST::Attribute &attr);
@@ -92,6 +93,9 @@ protected:
   handle_link_section_attribute_on_fndecl (tree fndecl,
 					   const AST::Attribute &attr);
 
+  static void handle_no_mangle_attribute_on_fndecl (tree fndecl,
+						    const AST::Attribute &attr);
+
   static void setup_abi_options (tree fndecl, ABI abi);
 
   static tree address_expression (tree, Location);

gcc/rust/util/rust-attributes.cc

@@ -32,6 +32,7 @@ static const BuiltinAttrDefinition __definitions[] = {
   {"must_use", STATIC_ANALYSIS},
   {"lang", HIR_LOWERING},
   {"link_section", CODE_GENERATION},
+  {"no_mangle", CODE_GENERATION},
 };
 
 BuiltinAttributeMappings *

gcc/testsuite/rust/debug/no_mangle.rs

@@ -0,0 +1,17 @@
+#[no_mangle]
+fn do_not_mangle() -> i32 {
+    0 
+}
+
+fn please_mangle() {}
+
+fn main() {
+// { dg-do compile }
+// { dg-options "-gdwarf-5 -dA" }
+    let _ = do_not_mangle();
+    please_mangle();
+// look for unmangled function name:
+// { dg-final { scan-assembler "do_not_mangle:" } } */
+// look for legacy mangled function name:
+// { dg-final { scan-assembler "13please_mangle" } } */
+}