Handle link_name attribute

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

@@ -24,6 +24,8 @@
 #include "rust-compile-type.h"
 #include "rust-diagnostics.h"
 #include "rust-hir-full-decls.h"
+#include "rust-attributes.h"
+#include "rust-attribute-values.h"
 
 namespace Rust {
 namespace Compile {
@@ -57,8 +59,7 @@ class CompileExternItem : public HIRCompileBase,
     rust_assert (ok);
 
     std::string name = item.get_item_name ().as_string ();
-    // FIXME this is assuming C ABI
-    std::string asm_name = name;
+    GGC::Ident asm_name = get_link_name (item);
 
     tree type = TyTyResolveCompile::compile (ctx, resolved_type);
     bool is_external = true;
@@ -124,16 +125,7 @@ class CompileExternItem : public HIRCompileBase,
 
     tree compiled_fn_type = TyTyResolveCompile::compile (ctx, fntype);
     std::string ir_symbol_name = function.get_item_name ().as_string ();
-    std::string asm_name = function.get_item_name ().as_string ();
-    if (fntype->get_abi () == ABI::RUST)
-      {
-	// then we need to get the canonical path of it and mangle it
-	auto canonical_path = ctx->get_mappings ().lookup_canonical_path (
-	  function.get_mappings ().get_nodeid ());
-
-	ir_symbol_name = canonical_path->get () + fntype->subst_as_string ();
-	asm_name = ctx->mangle_item (fntype, *canonical_path);
-      }
+    GGC::Ident asm_name = get_link_name (function);
 
     const unsigned int flags = Backend::function_is_declaration;
     tree fndecl = Backend::function (compiled_fn_type, ir_symbol_name, asm_name,
@@ -158,6 +150,36 @@ class CompileExternItem : public HIRCompileBase,
       ref_locus (ref_locus)
   {}
 
+  template <typename T> static GGC::Ident get_link_name (T &obj)
+  {
+    AST::Attribute *use_attr = nullptr;
+
+    for (auto &attr : obj.get_outer_attrs ())
+      {
+	if (attr.get_path ().as_string () == Values::Attributes::LINK_NAME)
+	  {
+	    // later attributes override earlier ones
+	    // TODO: add warning -- should duplicate
+	    //       attributes be folded elsewhere?
+	    use_attr = &attr;
+	  }
+      }
+
+    if (use_attr)
+      {
+	auto link_name
+	  = Analysis::Attributes::extract_string_literal (*use_attr);
+
+	if (!link_name.has_value ())
+	  rust_error_at (use_attr->get_locus (),
+			 "malformed %<link_name%> attribute input");
+	else
+	  return *link_name;
+      }
+
+    return obj.get_item_name ();
+  }
+
   TyTy::BaseType *concrete;
   tree reference;
   location_t ref_locus;

gcc/rust/util/rust-attribute-values.h

@@ -36,6 +36,7 @@ class Attributes
   static constexpr auto &DOC = "doc";
   static constexpr auto &MUST_USE = "must_use";
   static constexpr auto &LANG = "lang";
+  static constexpr auto &LINK_NAME = "link_name";
   static constexpr auto &LINK_SECTION = "link_section";
   static constexpr auto &NO_MANGLE = "no_mangle";
   static constexpr auto &REPR = "repr";

gcc/rust/util/rust-attributes.cc

@@ -78,6 +78,7 @@ static const BuiltinAttrDefinition __definitions[]
      {Attrs::DOC, HIR_LOWERING},
      {Attrs::MUST_USE, STATIC_ANALYSIS},
      {Attrs::LANG, HIR_LOWERING},
+     {Attrs::LINK_NAME, CODE_GENERATION},
      {Attrs::LINK_SECTION, CODE_GENERATION},
      {Attrs::NO_MANGLE, CODE_GENERATION},
      {Attrs::REPR, CODE_GENERATION},

gcc/rust/util/rust-ggc.cc

@@ -17,6 +17,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-ggc.h"
+#include "rust-ast.h"
 #include "stringpool.h"
 
 namespace Rust {
@@ -29,6 +30,8 @@ Ident::Ident (const std::string &str)
   : inner (get_identifier_with_length (str.c_str (), str.length ()))
 {}
 
+Ident::Ident (const Rust::Identifier &ident) : Ident (ident.as_string ()) {}
+
 bool
 Ident::operator== (const std::string &other) const
 {

gcc/rust/util/rust-ggc.h

@@ -24,6 +24,9 @@
 
 namespace Rust {
 
+// forward declare
+class Identifier;
+
 namespace GGC {
 
 class Ident
@@ -33,6 +36,7 @@ class Ident
 public:
   Ident (const char *str);
   Ident (const std::string &str);
+  Ident (const Rust::Identifier &ident);
 
   bool operator== (const Ident &other) const { return inner == other.inner; }
   bool operator== (const std::string &other) const;

gcc/testsuite/rust/execute/torture/link-name.rs

@@ -0,0 +1,16 @@
+// { dg-additional-options "-fdump-rtl-final" }
+// { dg-final { scan-rtl-dump "printf" "final" } }
+// { dg-output "gcc\r*\n" }
+
+extern "C" {
+    #[link_name = "printf"]
+    fn druckt(fmt: *const i8, ...);
+}
+
+fn main() -> i32 {
+    let a = "gcc\0";
+
+    unsafe { druckt("%s\n\0" as *const str as *const i8, a as *const str as *const i8); }
+
+    0
+}