pkg/ifuzz: fix generate/build

Currently the commands we have in go:generate first create an empty file
and then write final contents. This breaks any parallel builds of the source.
Even running go generate ./... does not work.
Write output files atomically.

2 files changed, 11 insertions, 5 deletions

diff --git a/pkg/ifuzz/arm64/arm64.go b/pkg/ifuzz/arm64/arm64.go
index 3b835566f..a2d326339 100644
--- a/pkg/ifuzz/arm64/arm64.go
+++ b/pkg/ifuzz/arm64/arm64.go
@@ -1,7 +1,7 @@
 // Copyright 2024 syzkaller project authors. All rights reserved.
 // Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
 
-//go:generate bash -c "go run gen/gen.go gen/json/arm64.json | gofmt > generated/insns.go"
+//go:generate go run gen/gen.go gen/json/arm64.json generated/insns.go
 
 // Package arm64 allows to generate and mutate arm64 machine code.
 package arm64
diff --git a/pkg/ifuzz/arm64/gen/gen.go b/pkg/ifuzz/arm64/gen/gen.go
index 659fea202..ef5afbd46 100644
--- a/pkg/ifuzz/arm64/gen/gen.go
+++ b/pkg/ifuzz/arm64/gen/gen.go
@@ -5,6 +5,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -12,13 +13,14 @@ import (
 	"strings"
 
 	"github.com/google/syzkaller/pkg/ifuzz/arm64"
+	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/pkg/serializer"
 	"github.com/google/syzkaller/pkg/tool"
 )
 
 func main() {
-	if len(os.Args) != 2 {
-		tool.Failf("usage: gen arm64.json")
+	if len(os.Args) != 3 {
+		tool.Failf("usage: gen arm64.json output.file")
 	}
 	jsonStr, err := os.ReadFile(os.Args[1])
 	if err != nil {
@@ -26,7 +28,8 @@ func main() {
 	}
 	insns := JSONToInsns(jsonStr)
 
-	fmt.Printf(`// Code generated by pkg/ifuzz/gen. DO NOT EDIT.
+	out := new(bytes.Buffer)
+	fmt.Fprintf(out, `// Code generated by pkg/ifuzz/gen. DO NOT EDIT.
 
 // go:build !codeanalysis
 
@@ -42,7 +45,10 @@ func init() {
 
 var insns_arm64 = 
 `)
-	serializer.Write(os.Stdout, insns)
+	serializer.Write(out, insns)
+	if err := osutil.WriteFileAtomically(os.Args[2], out.Bytes()); err != nil {
+		tool.Fail(err)
+	}
 
 	fmt.Fprintf(os.Stderr, "handled %v\n", len(insns))
 }