syscall: do not use NULL for zero-length read, write
Avoids problems running Linux binaries under QEMU.
R=r, gri
CC=golang-dev
https://golang.org/cl/4151043
diff --git a/src/pkg/syscall/syscall.go b/src/pkg/syscall/syscall.go
index 1647d69..9697537 100644
--- a/src/pkg/syscall/syscall.go
+++ b/src/pkg/syscall/syscall.go
@@ -24,3 +24,7 @@
// StringBytePtr returns a pointer to a NUL-terminated array of bytes
// containing the text of s.
func StringBytePtr(s string) *byte { return &StringByteSlice(s)[0] }
+
+// Single-word zero for use when we need a valid pointer to 0 bytes.
+// See mksyscall.sh.
+var _zero uintptr
