Move nmspinning address lookup to dynamic facts render

This removes the need to check the offset every release.

I've also removed the negative build tag from runtime_amd64.go, which less
obviously correct. In theory, we should check that this package's use of
nmspinning is still valid in each release, but there is no way to automate that
and I don't realistically seeing checking happening beyond verifying tests
work. Additionally, the existing use is already suspect. :)

The good news is the misuse is likely to cause scheduling issues, not memory
corruption.

PiperOrigin-RevId: 505114683

pkg/sync/BUILD

@@ -1,10 +1,33 @@
-load("//tools:defs.bzl", "go_library", "go_test")
+load("//tools:defs.bzl", "arch_genrule", "go_library", "go_test", "select_arch")
+load("//tools/nogo:defs.bzl", "nogo_facts")
 
 package(
     default_visibility = ["//:sandbox"],
     licenses = ["notice"],
 )
 
+nogo_facts(
+    name = "runtime_spinning_impl",
+    srcs = ["runtime.go"],
+    output = "runtime_spinning_impl.s",
+    template = select_arch(
+        amd64 = "runtime_spinning_amd64.s",
+        arm64 = "runtime_spinning_other.s",
+    ),
+)
+
+# For arm64 (or any !amd64), this will generate runtime_spinning_impl_arm64.s,
+# which is a copy of the (empty) runtime_spinning_other.s.
+#
+# On the go branch, only amd64 and arm64 will have have files, other arches
+# won't select any of these files. That is fine because the contents only
+# matter for amd64 anyway.
+arch_genrule(
+    name = "runtime_spinning_impl_arch",
+    src = ":runtime_spinning_impl",
+    template = "runtime_spinning_impl_%s.s",
+)
+
 go_library(
     name = "sync",
     srcs = [
@@ -21,12 +44,12 @@ go_library(
         "race_arm64.s",
         "race_unsafe.go",
         "runtime_amd64.go",
-        "runtime_amd64.s",
         "runtime_other.go",
         "runtime_unsafe.go",
         "rwmutex_unsafe.go",
         "seqcount.go",
         "sync.go",
+        ":runtime_spinning_impl_arch",
     ],
     marshal = False,
     stateify = False,

pkg/sync/runtime.go

@@ -0,0 +1,22 @@
+// Copyright 2023 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sync
+
+import (
+	"runtime"
+)
+
+// Dummy reference for facts.
+const _ = runtime.Compiler

pkg/sync/runtime_amd64.go

@@ -3,8 +3,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build amd64 && go1.8 && !go1.21 && !goexperiment.staticlockranking
-// +build amd64,go1.8,!go1.21,!goexperiment.staticlockranking
+//go:build amd64
 
 package sync
 

pkg/sync/runtime_spinning_amd64.s

@@ -12,14 +12,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build amd64 && go1.14 && !go1.21 && !goexperiment.staticlockranking
-// +build amd64,go1.14,!go1.21,!goexperiment.staticlockranking
+//go:build amd64
 
 #include "textflag.h"
 
+#define NMSPINNING_OFFSET {{ .import.runtime.schedt.nmspinning.Offset }}
+
 TEXT ·addrOfSpinning(SB),NOSPLIT,$0-8
-	// The offset specified here is the nmspinning value in sched.
 	LEAQ runtime·sched(SB), AX
-	ADDQ $92, AX
+	ADDQ $NMSPINNING_OFFSET, AX
 	MOVQ AX, ret+0(FP)
 	RET

pkg/sync/runtime_spinning_other.s

@@ -0,0 +1,18 @@
+// Copyright 2023 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !amd64
+
+// This file is intentionally left blank. Other arches don't use
+// addrOfSpinning, but we still need an input to the nogo temlate rule.