libgo patch committed: Fix NUL terminator check in socket length

[Ian Lance Taylor via Gcc-patches]

This libgo patch by Nikhil Benesch backports a fix for *BSD unix
sockets from the master sources.  *BSD does not include the null
terminator when in its reported socketlength.  Port the upstream
bugfix for the issue (https://golang.org/issue/6627).  This was likely
missed during the usual upstream merge because the gc and gccgo socket
implementations have diverged quite a bit.  Bootstrapped and ran Go
testsuite on x86_64-pc-linux-gnu.  Committed to mainline.

Ian

1f15bcd13f4019744deec3140b575101fbd651ba
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 8f71939862b..80e702fc3f5 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-fef8afc1876f4a1d5e9a8fd54c21bf5917966e10
+5e76d81ec120e05a59e6c7d173ddf8a3de466bd0
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/libgo/go/syscall/socket_bsd.go b/libgo/go/syscall/socket_bsd.go
index f62457f2bdb..40637bc7818 100644
--- a/libgo/go/syscall/socket_bsd.go
+++ b/libgo/go/syscall/socket_bsd.go
@@ -52,13 +52,19 @@ func (sa *RawSockaddrUnix) setLen(n int) {
 }
 
 func (sa *RawSockaddrUnix) getLen() (int, error) {
-       if sa.Len < 3 || sa.Len > SizeofSockaddrUnix {
+       if sa.Len < 2 || sa.Len > SizeofSockaddrUnix {
                return 0, EINVAL
        }
-       n := int(sa.Len) - 3 // subtract leading Family, Len, terminating NUL.
+
+       // Some BSDs include the trailing NUL in the length, whereas
+       // others do not. Work around this by subtracting the leading
+       // family and len. The path is then scanned to see if a NUL
+       // terminator still exists within the length.
+       n := int(sa.Len) - 2 // subtract leading Family, Len
        for i := 0; i < n; i++ {
                if sa.Path[i] == 0 {
-                       // found early NUL; assume Len is overestimating.
+                       // found early NUL; assume Len included the NUL
+                       // or was overestimating.
                        n = i
                        break
                }