runtime: do not split stacks in syscall status

Split stack checks (morestack) corrupt g->sched,
but g->sched must be preserved consistent for GC/traceback.
The change implements runtime.notetsleepg function,
which does entersyscall/exitsyscall and is carefully arranged
to not call any split functions in between.

R=rsc
CC=golang-dev
https://golang.org/cl/11575044

1 files changed, 30 insertions, 0 deletions

diff --git a/src/pkg/runtime/runtime.c b/src/pkg/runtime/runtime.c
index 9b5f6c8ca3..03a9daf4c2 100644
--- a/src/pkg/runtime/runtime.c
+++ b/src/pkg/runtime/runtime.c
@@ -220,6 +220,9 @@ runtime·check(void)
 	if(offsetof(struct y1, y) != 1) runtime·throw("bad offsetof y1.y");
 	if(sizeof(struct y1) != 2) runtime·throw("bad sizeof y1");
 
+	if(runtime·timediv(12345LL*1000000000+54321, 1000000000, &e) != 12345 || e != 54321)
+		runtime·throw("bad timediv");
+
 	uint32 z;
 	z = 1;
 	if(!runtime·cas(&z, 1, 2))
@@ -407,3 +410,30 @@ runtime·parsedebugvars(void)
 		p++;
 	}
 }
+
+// Poor mans 64-bit division.
+// This is a very special function, do not use it if you are not sure what you are doing.
+// int64 division is lowered into _divv() call on 386, which does not fit into nosplit functions.
+// Handles overflow in a time-specific manner.
+#pragma textflag 7
+int32
+runtime·timediv(int64 v, int32 div, int32 *rem)
+{
+	int32 res, bit;
+
+	if(v >= div*0x7fffffffLL) {
+		if(rem != nil)
+			*rem = 0;
+		return 0x7fffffff;
+	}
+	res = 0;
+	for(bit = 0x40000000; bit != 0; bit >>= 1) {
+		if(v >= (int64)bit*div) {
+			v -= (int64)bit*div;
+			res += bit;
+		}
+	}
+	if(rem != nil)
+		*rem = v;
+	return res;
+}