runtime: introduce and consistently use setNsec for timespec

The general code for setting a timespec value sometimes used set_nsec
and sometimes used a combination of set_sec and set_nsec. Standardize
on a setNsec function that takes a number of nanoseconds and splits
them up to set the tv_sec and tv_nsec fields. Consistently mark
setNsec as go:nosplit, since it has to be that way on some systems
including Darwin and GNU/Linux. Consistently use timediv on 32-bit
systems to help stay within split-stack limits on processors that
don't have a 64-bit division instruction.

Change-Id: I6396bb7ddbef171a96876bdeaf7a1c585a6d725b
Reviewed-on: https://go-review.googlesource.com/c/go/+/167389
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 2 insertions, 15 deletions

diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go
index a04c995c00..8f3afe0577 100644
--- a/src/runtime/os_linux.go
+++ b/src/runtime/os_linux.go
@@ -35,8 +35,6 @@ const (
 // Don't sleep longer than ns; ns < 0 means forever.
 //go:nosplit
 func futexsleep(addr *uint32, val uint32, ns int64) {
-	var ts timespec
-
 	// Some Linux kernels have a bug where futex of
 	// FUTEX_WAIT returns an internal error code
 	// as an errno. Libpthread ignores the return value
@@ -47,19 +45,8 @@ func futexsleep(addr *uint32, val uint32, ns int64) {
 		return
 	}
 
-	// It's difficult to live within the no-split stack limits here.
-	// On ARM and 386, a 64-bit divide invokes a general software routine
-	// that needs more stack than we can afford. So we use timediv instead.
-	// But on real 64-bit systems, where words are larger but the stack limit
-	// is not, even timediv is too heavy, and we really need to use just an
-	// ordinary machine instruction.
-	if sys.PtrSize == 8 {
-		ts.set_sec(ns / 1000000000)
-		ts.set_nsec(int32(ns % 1000000000))
-	} else {
-		ts.tv_nsec = 0
-		ts.set_sec(int64(timediv(ns, 1000000000, (*int32)(unsafe.Pointer(&ts.tv_nsec)))))
-	}
+	var ts timespec
+	ts.setNsec(ns)
 	futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, unsafe.Pointer(&ts), nil, 0)
 }