runtime: move arm hardware division support detection to internal/cpu

Assumes mandatory VFP and VFPv3 support to be present by default
but not IDIVA if AT_HWCAP is not available.

Adds GODEBUGCPU options to disable the use of code paths in the runtime
that use hardware support for division.

Change-Id: Ida02311bd9b9701de3fc120697e69445bf6c0853
Reviewed-on: https://go-review.googlesource.com/114826
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 10 insertions, 9 deletions

diff --git a/src/runtime/os_linux_arm.go b/src/runtime/os_linux_arm.go
index 14f1cfeaef..8f082ba6a0 100644
--- a/src/runtime/os_linux_arm.go
+++ b/src/runtime/os_linux_arm.go
@@ -4,20 +4,20 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"internal/cpu"
+	"unsafe"
+)
 
 const (
 	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
 
 	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
 	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
-	_HWCAP_IDIVA = 1 << 17
 )
 
 var randomNumber uint32
 var armArch uint8 = 6 // we default to ARMv6
-var hwcap uint32      // set by archauxv
-var hardDiv bool      // set if a hardware divider is available
 
 func checkgoarm() {
 	// On Android, /proc/self/auxv might be unreadable and hwcap won't
@@ -26,12 +26,12 @@ func checkgoarm() {
 	if GOOS == "android" {
 		return
 	}
-	if goarm > 5 && hwcap&_HWCAP_VFP == 0 {
+	if goarm > 5 && cpu.HWCap&_HWCAP_VFP == 0 {
 		print("runtime: this CPU has no floating point hardware, so it cannot run\n")
 		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
 		exit(1)
 	}
-	if goarm > 6 && hwcap&_HWCAP_VFPv3 == 0 {
+	if goarm > 6 && cpu.HWCap&_HWCAP_VFPv3 == 0 {
 		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
 		print("this GOARM=", goarm, " binary. Recompile using GOARM=5 or GOARM=6.\n")
 		exit(1)
@@ -53,9 +53,10 @@ func archauxv(tag, val uintptr) {
 			armArch = t - '0'
 		}
 
-	case _AT_HWCAP: // CPU capability bit flags
-		hwcap = uint32(val)
-		hardDiv = (hwcap & _HWCAP_IDIVA) != 0
+	case _AT_HWCAP:
+		cpu.HWCap = uint(val)
+	case _AT_HWCAP2:
+		cpu.HWCap2 = uint(val)
 	}
 }