From 01dd57b3125892e0dc2054436f29cafb38b0a3ef Mon Sep 17 00:00:00 2001
From: Julian Phillips <julian@quantumfyre.co.uk>
Date: Tue, 16 Aug 2011 14:56:23 -0400
Subject: [PATCH] cgo: omit duplicate symbols in writeDefs

When the C API being used includes multiple names for the same
underlying symbol (e.g. multiple #define's for the same variable), then
cgo will generate the same placeholder variables for each name.  This
then prevents the code from compiling due to multiple declarations of
the same variable - so change cgo to only create one instance of the
variable for the underlying symbol.

R=rsc
CC=golang-dev
https://golang.org/cl/4826055
---
 misc/cgo/test/Makefile            |  1 +
 misc/cgo/test/duplicate_symbol.go | 21 +++++++++++++++++++++
 src/cmd/cgo/out.go                | 14 +++++++++-----
 3 files changed, 31 insertions(+), 5 deletions(-)
 create mode 100644 misc/cgo/test/duplicate_symbol.go

diff --git a/misc/cgo/test/Makefile b/misc/cgo/test/Makefile
index f26f972898..d4309be3c6 100644
--- a/misc/cgo/test/Makefile
+++ b/misc/cgo/test/Makefile
@@ -15,6 +15,7 @@ CGOFILES=\
 	issue1222.go\
 	issue1328.go\
 	issue1560.go\
+	duplicate_symbol.go\
 
 CGO_OFILES=\
 	callback_c.o\
diff --git a/misc/cgo/test/duplicate_symbol.go b/misc/cgo/test/duplicate_symbol.go
new file mode 100644
index 0000000000..69600de9cb
--- /dev/null
+++ b/misc/cgo/test/duplicate_symbol.go
@@ -0,0 +1,21 @@
+// Copyright 2010 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains test cases for cgo.
+
+package cgotest
+
+/*
+int base_symbol = 0;
+
+#define alias_one base_symbol
+#define alias_two base_symbol
+*/
+import "C"
+
+import "fmt"
+
+func duplicateSymbols() {
+	fmt.Printf("%v %v %v\n", C.base_symbol, C.alias_one, C.alias_two)
+}
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 9c962b8ff9..498ab1566b 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -59,17 +59,21 @@ func (p *Package) writeDefs() {
 
 	fmt.Fprintf(fc, cProlog)
 
-	var cVars []string
+	cVars := make(map[string]bool)
 	for _, n := range p.Name {
 		if n.Kind != "var" {
 			continue
 		}
-		cVars = append(cVars, n.C)
 
-		fmt.Fprintf(fm, "extern char %s[];\n", n.C)
-		fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+		if !cVars[n.C] {
+			fmt.Fprintf(fm, "extern char %s[];\n", n.C)
+			fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+
+			fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
+
+			cVars[n.C] = true
+		}
 
-		fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
 		fmt.Fprintf(fc, "void *·%s = &%s;\n", n.Mangle, n.C)
 		fmt.Fprintf(fc, "\n")
 
-- 
2.48.1