compiler, libgo: Use //extern comments rather than __asm__.

From-SVN: r183981

5 files changed, 76 insertions, 12 deletions

diff --git a/gcc/go/ChangeLog b/gcc/go/ChangeLog
index 04ac6ac..40afb84 100644
--- a/gcc/go/ChangeLog
+++ b/gcc/go/ChangeLog
@@ -1,3 +1,8 @@
+2012-02-07  Ian Lance Taylor  <iant@google.com>
+
+	* gccgo.texi (Function Names): Document //extern instead of
+	__asm__.
+
 2012-02-01  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/52079
diff --git a/gcc/go/gccgo.texi b/gcc/go/gccgo.texi
index dc8b022..13b56fc 100644
--- a/gcc/go/gccgo.texi
+++ b/gcc/go/gccgo.texi
@@ -304,14 +304,20 @@ function is still using it.
 @node Function Names
 @section Function Names
 
-@cindex @code{__asm__}
+@cindex @code{extern}
+@cindex external names
 Go code can call C functions directly using a Go extension implemented
-in @command{gccgo}: a function declaration may be followed by
-@code{__asm__ ("@var{name}")}. For example, here is how the C function
-@code{open} can be declared in Go:
+in @command{gccgo}: a function declaration may be preceded by a
+comment giving the external name.  The comment must be at the
+beginning of the line and must start with @code{//extern}.  This must
+be followed by a space and then the external name of the function.
+The function declaration must be on the line immediately after the
+comment.  For example, here is how the C function @code{open} can be
+declared in Go:
 
 @smallexample
-func c_open(name *byte, mode int, perm int) int __asm__ ("open");
+//extern open
+func c_open(name *byte, mode int, perm int) int
 @end smallexample
 
 The C function naturally expects a nul terminated string, which in Go
@@ -333,7 +339,7 @@ present the name of a Go function that does not have a receiver is
 @option{-fgo-prefix} option used when the package is compiled; if the
 option is not used, the default is simply @code{go}.  To call the
 function from C you must set the name using the @command{gcc}
-extension similar to the @command{gccgo} extension.
+@code{__asm__} extension.
 
 @smallexample
 extern int go_function(int) __asm__ ("myprefix.mypackage.Function");
diff --git a/gcc/go/gofrontend/lex.cc b/gcc/go/gofrontend/lex.cc
index d46334f..53618fc 100644
--- a/gcc/go/gofrontend/lex.cc
+++ b/gcc/go/gofrontend/lex.cc
@@ -442,7 +442,7 @@ Token::print(FILE* file) const
 Lex::Lex(const char* input_file_name, FILE* input_file, Linemap* linemap)
   : input_file_name_(input_file_name), input_file_(input_file),
     linemap_(linemap), linebuf_(NULL), linebufsize_(120), linesize_(0),
-    lineoff_(0), lineno_(0), add_semi_at_eol_(false)
+    lineoff_(0), lineno_(0), add_semi_at_eol_(false), extern_()
 {
   this->linebuf_ = new char[this->linebufsize_];
   this->linemap_->start_file(input_file_name, 0);
@@ -541,6 +541,7 @@ Lex::earlier_location(int chars) const
 Token
 Lex::next_token()
 {
+  bool saw_cpp_comment = false;
   while (true)
     {
       if (!this->require_line())
@@ -552,6 +553,10 @@ Lex::next_token()
 	  return this->make_eof_token();
 	}
 
+      if (!saw_cpp_comment)
+	this->extern_.clear();
+      saw_cpp_comment = false;
+
       const char* p = this->linebuf_ + this->lineoff_;
       const char* pend = this->linebuf_ + this->linesize_;
 
@@ -588,6 +593,7 @@ Lex::next_token()
 		  p = pend;
 		  if (p[-1] == '\n' && this->add_semi_at_eol_)
 		    --p;
+		  saw_cpp_comment = true;
 		}
 	      else if (p[1] == '*')
 		{
@@ -1606,6 +1612,10 @@ Lex::skip_c_comment()
 void
 Lex::skip_cpp_comment()
 {
+  // Ensure that if EXTERN_ is set, it means that we just saw a
+  // //extern comment.
+  this->extern_.clear();
+
   const char* p = this->linebuf_ + this->lineoff_;
   const char* pend = this->linebuf_ + this->linesize_;
 
@@ -1648,12 +1658,35 @@ Lex::skip_cpp_comment()
 	}
     }
 
+  // As a special gccgo extension, a C++ comment at the start of the
+  // line of the form
+  //   //extern NAME
+  // which immediately precedes a function declaration means that the
+  // external name of the function declaration is NAME.  This is
+  // normally used to permit Go code to call a C function.
+  if (this->lineoff_ == 2
+      && pend - p > 7
+      && memcmp(p, "extern ", 7) == 0)
+    {
+      p += 7;
+      while (p < pend && (*p == ' ' || *p == '\t'))
+	++p;
+      const char* plend = pend;
+      while (plend > p
+	     && (plend[-1] == ' ' || plend[-1] == '\t' || plend[-1] == '\n'))
+	--plend;
+      if (plend > p)
+	this->extern_ = std::string(p, plend - p);
+    }
+
   while (p < pend)
     {
       this->lineoff_ = p - this->linebuf_;
       unsigned int c;
       bool issued_error;
       p = this->advance_one_utf8_char(p, &c, &issued_error);
+      if (issued_error)
+	this->extern_.clear();
     }
 }
 
diff --git a/gcc/go/gofrontend/lex.h b/gcc/go/gofrontend/lex.h
index b184b1e..8858e73 100644
--- a/gcc/go/gofrontend/lex.h
+++ b/gcc/go/gofrontend/lex.h
@@ -344,6 +344,11 @@ class Lex
   Token
   next_token();
 
+  // Return the contents of any current //extern comment.
+  const std::string&
+  extern_name() const
+  { return this->extern_; }
+
   // Return whether the identifier NAME should be exported.  NAME is a
   // mangled name which includes only ASCII characters.
   static bool
@@ -474,6 +479,9 @@ class Lex
   size_t lineno_;
   // Whether to add a semicolon if we see a newline now.
   bool add_semi_at_eol_;
+  // The external name to use for a function declaration, from a magic
+  // //extern comment.
+  std::string extern_;
 };
 
 #endif // !defined(GO_LEX_H)
diff --git a/gcc/go/gofrontend/parse.cc b/gcc/go/gofrontend/parse.cc
index 10abfc0..6eb1981 100644
--- a/gcc/go/gofrontend/parse.cc
+++ b/gcc/go/gofrontend/parse.cc
@@ -2093,17 +2093,19 @@ Parse::simple_var_decl_or_assignment(const std::string& name,
 // FunctionDecl = "func" identifier Signature [ Block ] .
 // MethodDecl = "func" Receiver identifier Signature [ Block ] .
 
-// gcc extension:
+// Deprecated gcc extension:
 //   FunctionDecl = "func" identifier Signature
 //                    __asm__ "(" string_lit ")" .
 // This extension means a function whose real name is the identifier
-// inside the asm.
+// inside the asm.  This extension will be removed at some future
+// date.  It has been replaced with //extern comments.
 
 void
 Parse::function_decl()
 {
   go_assert(this->peek_token()->is_keyword(KEYWORD_FUNC));
   Location location = this->location();
+  std::string extern_name = this->lex_->extern_name();
   const Token* token = this->advance_token();
 
   Typed_identifier* rec = NULL;
@@ -2173,10 +2175,20 @@ Parse::function_decl()
     {
       if (named_object == NULL && !Gogo::is_sink_name(name))
 	{
-	  if (fntype != NULL)
-	    this->gogo_->declare_function(name, fntype, location);
-	  else
+	  if (fntype == NULL)
 	    this->gogo_->add_erroneous_name(name);
+	  else
+	    {
+	      named_object = this->gogo_->declare_function(name, fntype,
+							   location);
+	      if (!extern_name.empty()
+		  && named_object->is_function_declaration())
+		{
+		  Function_declaration* fd =
+		    named_object->func_declaration_value();
+		  fd->set_asm_name(extern_name);
+		}
+	    }
 	}
     }
   else