cpu: add gccgo implementation

It uses __get_cpuid_count, provided by cpuid.h.
The xgetbv is implemented after its counterpart in cpu_x86.s.

Change-Id: I97624d7da67ab4ec3c9a53b0bfc4dfcdf7d12c87
Reviewed-on: https://go-review.googlesource.com/116155Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

cpu/cpu_gccgo.c

+// Copyright 2018 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.
+
+// +build 386 amd64 amd64p32
+// +build gccgo
+
+#include <cpuid.h>
+#include <stdint.h>
+
+// Need to wrap __get_cpuid_count because it's declared as static.
+int
+gccgoGetCpuidCount(uint32_t leaf, uint32_t subleaf,
+                   uint32_t *eax, uint32_t *ebx,
+                   uint32_t *ecx, uint32_t *edx)
+{
+	return __get_cpuid_count(leaf, subleaf, eax, ebx, ecx, edx);
+}
+
+// xgetbv reads the contents of an XCR (Extended Control Register)
+// specified in the ECX register into registers EDX:EAX.
+// Currently, the only supported value for XCR is 0.
+//
+// TODO: Replace with a better alternative:
+//
+//     #include <xsaveintrin.h>
+//
+//     #pragma GCC target("xsave")
+//
+//     void gccgoXgetbv(uint32_t *eax, uint32_t *edx) {
+//       unsigned long long x = _xgetbv(0);
+//       *eax = x & 0xffffffff;
+//       *edx = (x >> 32) & 0xffffffff;
+//     }
+//
+// Note that _xgetbv is defined starting with GCC 8.
+void
+gccgoXgetbv(uint32_t *eax, uint32_t *edx)
+{
+	__asm("  xorl %%ecx, %%ecx\n"
+	      "  xgetbv"
+	    : "=a"(*eax), "=d"(*edx));
+}

cpu/cpu_gccgo.go

+// Copyright 2018 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.
+
+// +build 386 amd64 amd64p32
+// +build gccgo
+
+package cpu
+
+//extern gccgoGetCpuidCount
+func gccgoGetCpuidCount(eaxArg, ecxArg uint32, eax, ebx, ecx, edx *uint32)
+
+func cpuid(eaxArg, ecxArg uint32) (eax, ebx, ecx, edx uint32) {
+	var a, b, c, d uint32
+	gccgoGetCpuidCount(eaxArg, ecxArg, &a, &b, &c, &d)
+	return a, b, c, d
+}
+
+//extern gccgoXgetbv
+func gccgoXgetbv(eax, edx *uint32)
+
+func xgetbv() (eax, edx uint32) {
+	var a, d uint32
+	gccgoXgetbv(&a, &d)
+	return a, d
+}

cpu/cpu_x86.go

@@ -8,10 +8,12 @@ package cpu
 
 const cacheLineSize = 64
 
-// cpuid is implemented in cpu_x86.s.
+// cpuid is implemented in cpu_x86.s for gc compiler
+// and in cpu_gccgo.c for gccgo.
 func cpuid(eaxArg, ecxArg uint32) (eax, ebx, ecx, edx uint32)
 
-// xgetbv with ecx = 0 is implemented in cpu_x86.s.
+// xgetbv with ecx = 0 is implemented in cpu_x86.s for gc compiler
+// and in cpu_gccgo.c for gccgo.
 func xgetbv() (eax, edx uint32)
 
 func init() {

cpu/cpu_x86.s

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build 386 amd64 amd64p32
+// +build !gccgo
 
 #include "textflag.h"