runtime: stop plan9/amd64 build from crashing

LGTM=iant
R=rsc, 0intro, alex.brainman, iant
CC=golang-codereviews
https://golang.org/cl/140460044

diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 1a106dc1f1d4a3876093a5c36f7bb85a06b69403..e5702d074c0550603cc53cc0aaa7746121dd260a 100644 (file)
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -272,6 +272,7 @@ onm:
 // record an argument size. For that purpose, it has no arguments.
 TEXT runtime·morestack(SB),NOSPLIT,$0-0
        // Cannot grow scheduler stack (m->g0).
+       get_tls(CX)
        MOVQ    g(CX), BX
        MOVQ    g_m(BX), BX
        MOVQ    m_g0(BX), SI