Add in-kernel test runner

This adds a way to run tests inside the Smalltown kernel.

Improvements to the Bazel part of this are tracked in T726

Test Plan: Tested by intentionally failing the test.

X-Origin-Diff: phab/D485
GitOrigin-RevId: e4aad7f28d122d82a7fcb6699e678cbe022e2f73
diff --git a/core/tools/kconfig-patcher/main.go b/core/tools/kconfig-patcher/main.go
new file mode 100644
index 0000000..27c33e9
--- /dev/null
+++ b/core/tools/kconfig-patcher/main.go
@@ -0,0 +1,95 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// 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 main
+
+import (
+	"bufio"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+var (
+	inPath  = flag.String("in", "", "Path to input Kconfig")
+	outPath = flag.String("out", "", "Path to output Kconfig")
+)
+
+func main() {
+	flag.Parse()
+	if *inPath == "" || *outPath == "" {
+		flag.PrintDefaults()
+		os.Exit(2)
+	}
+	inFile, err := os.Open(*inPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to open input Kconfig: %v\n", err)
+		os.Exit(1)
+	}
+	outFile, err := os.Create(*outPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to create output Kconfig: %v\n", err)
+		os.Exit(1)
+	}
+	var config struct {
+		Overrides map[string]string `json:"overrides"`
+	}
+	if err := json.Unmarshal([]byte(flag.Arg(0)), &config); err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to parse overrides: %v\n", err)
+		os.Exit(1)
+	}
+	err = patchKconfig(inFile, outFile, config.Overrides)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to patch: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func patchKconfig(inFile io.Reader, outFile io.Writer, overrides map[string]string) error {
+	scanner := bufio.NewScanner(inFile)
+	for scanner.Scan() {
+		line := scanner.Text()
+		cleanLine := strings.TrimSpace(line)
+		if strings.HasPrefix(cleanLine, "#") || cleanLine == "" {
+			// Pass through comments and empty lines
+			fmt.Fprintln(outFile, line)
+		} else {
+			// Line contains a configuration option
+			parts := strings.SplitN(line, "=", 2)
+			keyName := parts[0]
+			if overrideVal, ok := overrides[strings.TrimSpace(keyName)]; ok {
+				// Override it
+				if overrideVal == "" {
+					fmt.Fprintf(outFile, "# %v is not set\n", keyName)
+				} else {
+					fmt.Fprintf(outFile, "%v=%v\n", keyName, overrideVal)
+				}
+				delete(overrides, keyName)
+			} else {
+				// Pass through unchanged
+				fmt.Fprintln(outFile, line)
+			}
+		}
+	}
+	// Process left over overrides
+	for key, val := range overrides {
+		fmt.Fprintf(outFile, "%v=%v\n", key, val)
+	}
+	return nil
+}