runtime: fix cgo callbacks on windows
Fixes #4955.
R=golang-dev, alex.brainman
CC=golang-dev
https://golang.org/cl/7563043
diff --git a/src/pkg/runtime/sys_windows_amd64.s b/src/pkg/runtime/sys_windows_amd64.s
index fe88f3b..c20a268 100644
--- a/src/pkg/runtime/sys_windows_amd64.s
+++ b/src/pkg/runtime/sys_windows_amd64.s
@@ -346,3 +346,35 @@
TEXT runtime·remove_exception_handler(SB),7,$0
RET
+
+TEXT runtime·osyield(SB),7,$8
+ // Tried NtYieldExecution but it doesn't yield hard enough.
+ // NtWaitForSingleObject being used here as Sleep(0).
+ // The CALL is safe because NtXxx is a system call wrapper:
+ // it puts the right system call number in AX, then does
+ // a SYSENTER and a RET.
+ MOVQ runtime·NtWaitForSingleObject(SB), AX
+ MOVQ $1, BX
+ NEGQ BX
+ MOVQ SP, R8 // ptime
+ MOVQ BX, (R8)
+ MOVQ $-1, CX // handle
+ MOVQ $0, DX // alertable
+ CALL AX
+ RET
+
+TEXT runtime·usleep(SB),7,$8
+ // The CALL is safe because NtXxx is a system call wrapper:
+ // it puts the right system call number in AX, then does
+ // a SYSENTER and a RET.
+ MOVQ runtime·NtWaitForSingleObject(SB), AX
+ // Have 1us units; want negative 100ns units.
+ MOVL usec+0(FP), BX
+ IMULQ $10, BX
+ NEGQ BX
+ MOVQ SP, R8 // ptime
+ MOVQ BX, (R8)
+ MOVQ $-1, CX // handle
+ MOVQ $0, DX // alertable
+ CALL AX
+ RET
