[dev.cc] runtime: convert operating system support code from C to Go

The conversion was done with an automated tool and then
modified only as necessary to make it compile and run.

[This CL is part of the removal of C code from package runtime.
See golang.org/s/dev.cc for an overview.]

LGTM=r
R=r
CC=austin, dvyukov, golang-codereviews, iant, khr
https://codereview.appspot.com/174830044

1 files changed, 75 insertions, 0 deletions

diff --git a/src/runtime/os_linux_arm.go b/src/runtime/os_linux_arm.go
new file mode 100644
index 000000000..9b0ade614
--- /dev/null
+++ b/src/runtime/os_linux_arm.go
@@ -0,0 +1,75 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "unsafe"
+
+const (
+	_AT_NULL     = 0
+	_AT_PLATFORM = 15 //  introduced in at least 2.6.11
+	_AT_HWCAP    = 16 // introduced in at least 2.6.11
+	_AT_RANDOM   = 25 // introduced in 2.6.29
+
+	_HWCAP_VFP   = 1 << 6  // introduced in at least 2.6.11
+	_HWCAP_VFPv3 = 1 << 13 // introduced in 2.6.30
+)
+
+var randomNumber uint32
+var armArch uint8 = 6 // we default to ARMv6
+var hwcap uint32      // set by setup_auxv
+var goarm uint8       // set by 5l
+
+func checkgoarm() {
+	if goarm > 5 && 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 {
+		print("runtime: this CPU has no VFPv3 floating point hardware, so it cannot run\n")
+		print("this GOARM=", goarm, " binary. Recompile using GOARM=5.\n")
+		exit(1)
+	}
+}
+
+//go:nosplit
+func setup_auxv(argc int32, argv **byte) {
+	// skip over argv, envv to get to auxv
+	n := argc + 1
+	for argv_index(argv, n) != nil {
+		n++
+	}
+	n++
+	auxv := (*[1 << 28]uint32)(add(unsafe.Pointer(argv), uintptr(n)*ptrSize))
+
+	for i := 0; auxv[i] != _AT_NULL; i += 2 {
+		switch auxv[i] {
+		case _AT_RANDOM: // kernel provided 16-byte worth of random data
+			if auxv[i+1] != 0 {
+				randomNumber = *(*uint32)(unsafe.Pointer(uintptr(auxv[i+1])))
+			}
+
+		case _AT_PLATFORM: // v5l, v6l, v7l
+			t := *(*uint8)(unsafe.Pointer(uintptr(auxv[i+1] + 1)))
+			if '5' <= t && t <= '7' {
+				armArch = t - '0'
+			}
+
+		case _AT_HWCAP: // CPU capability bit flags
+			hwcap = auxv[i+1]
+		}
+	}
+}
+
+func cputicks() int64 {
+	// Currently cputicks() is used in blocking profiler and to seed fastrand1().
+	// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
+	// randomNumber provides better seeding of fastrand1.
+	return nanotime() + int64(randomNumber)
+}