From e636f6f51c073b7539b01fc2fcc7c17e25e29294 Mon Sep 17 00:00:00 2001
From: Mikio Hara <mikioh.mikioh@gmail.com>
Date: Thu, 22 Dec 2011 23:18:34 +0900
Subject: [PATCH] cmd/gc: make sure use of pthread for gcc-4.5 and beyond

R=golang-dev, rsc, n13m3y3r, rogpeppe
CC=golang-dev
https://golang.org/cl/5501060
---
 src/cmd/go/build.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index b79a522dc90..62c8d90d304 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -912,6 +912,16 @@ func (b *builder) gccCmd(objdir string, flags []string, args ...string) []string
 	case "6":
 		a = append(a, "-m64")
 	}
+	// gcc-4.5 and beyond require explicit "-pthread" flag
+	// for multithreading with pthread library.
+	if build.DefaultContext.CgoEnabled {
+		switch b.goos {
+		case "windows":
+			a = append(a, "-mthread")
+		default:
+			a = append(a, "-pthread")
+		}
+	}
 	a = append(a, flags...)
 	return append(a, args...)
 }