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/ktest/BUILD b/core/tools/ktest/BUILD
new file mode 100644
index 0000000..e139a18
--- /dev/null
+++ b/core/tools/ktest/BUILD
@@ -0,0 +1,62 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("//core/tools/kconfig-patcher:kconfig-patcher.bzl", "kconfig_patch")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["main.go"],
+    importpath = "git.monogon.dev/source/nexantic.git/core/tools/ktest",
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "ktest",
+    embed = [":go_default_library"],
+    pure = "on",
+    visibility = ["//visibility:public"],
+)
+
+kconfig_patch(
+    name = "testing-config",
+    src = "//third_party/linux:kernel-config",
+    out = "testing.config",
+    override_configs = {
+        # Unlock command line
+        "CONFIG_CMDLINE_OVERRIDE": "n",
+        "CONFIG_CMDLINE_BOOL": "n",
+        # Shave off 1 second from boot time
+        "CONFIG_SERIO_I8042": "",
+        "CONFIG_KEYBOARD_ATKBD": "",
+        "CONFIG_RTC_DRV_CMOS": "",
+        # Shave off an additional 18ms (half of the boot time)
+        "CONFIG_DEBUG_WX": "",
+    },
+)
+
+genrule(
+    name = "linux-testing",
+    srcs = [
+        "@linux//:all",
+        ":testing-config",
+    ],
+    outs = [
+        "linux-testing.elf",
+    ],
+    cmd = """
+    DIR=external/linux
+
+    mkdir $$DIR/.bin
+
+    cp $(location :testing-config) $$DIR/.config
+
+    (cd $$DIR && make -j $$(nproc) vmlinux >/dev/null)
+
+    cp $$DIR/vmlinux $@
+    """,
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "test-script",
+    srcs = ["run_ktest.sh"],
+    visibility = ["//visibility:public"],
+)