Kernel: Separate panic behavior from bootmode

Bootmode used to control panic behavior and SystemServer.
This patch factors panic behavior control into a separate flag.

.github/workflows/cmake.yml

@@ -183,7 +183,7 @@ jobs:
         working-directory: ${{ github.workspace }}/Build/${{ matrix.arch }}
         env:
           SERENITY_QEMU_CPU: "max,vmx=off"
-          SERENITY_KERNEL_CMDLINE: "fbdev=off boot_mode=self-test"
+          SERENITY_KERNEL_CMDLINE: "fbdev=off panic=shutdown boot_mode=self-test"
           SERENITY_RUN: "ci"
         run: |
           echo "::group::ninja run # Qemu output"

Base/usr/share/man/man7/boot_parameters.md

@@ -51,6 +51,8 @@ List of options:
 * **`init_args`** - This parameter expects a set of arguments to pass to the **`init`** program.
   The value should be a set of strings separated by `,` characters.
 
+* **`panic`** - This parameter expects **`halt`** or **`shutdown`**. This is particularly useful in CI contexts.
+
 * **`pci_ecam`** - This parameter expects **`on`** or **`off`**.
 
 * **`root`** - This parameter configures the device to use as the root file system. It defaults to **`/dev/hda`** if unspecified.

Documentation/RunningTests.md

@@ -110,7 +110,8 @@ the serial debug output to `./debug.log` so that both stdout of the tests and th
 captured.
 
 To run with CI's TestRunner system server entry, SerenityOS needs booted in self-test mode. Running the following shell
-lines will boot SerenityOS in self-test mode, run tests, and exit.
+lines will boot SerenityOS in self-test mode, run tests, and exit. Note that CI also sets `panic=shutdown` to terminate qemu;
+the default value `halt` keeps qemu around, which allows you to inspect the state.
 
 ```sh
 export SERENITY_RUN=ci

Kernel/CommandLine.cpp

@@ -38,8 +38,9 @@ UNMAP_AFTER_INIT void CommandLine::initialize()
     VERIFY(!s_the);
     s_the = new CommandLine(s_cmd_line);
     dmesgln("Kernel Commandline: {}", kernel_command_line().string());
-    // Validate the boot mode the user passed in.
+    // Validate the modes the user passed in.
     (void)s_the->boot_mode(Validate::Yes);
+    (void)s_the->panic_mode(Validate::Yes);
 }
 
 UNMAP_AFTER_INIT void CommandLine::build_commandline(const String& cmdline_from_bootloader)
@@ -214,6 +215,21 @@ BootMode CommandLine::boot_mode(Validate should_validate) const
     return BootMode::Unknown;
 }
 
+PanicMode CommandLine::panic_mode(Validate should_validate) const
+{
+    const auto panic_mode = lookup("panic"sv).value_or("halt"sv);
+    if (panic_mode == "halt"sv) {
+        return PanicMode::Halt;
+    } else if (panic_mode == "shutdown"sv) {
+        return PanicMode::Shutdown;
+    }
+
+    if (should_validate == Validate::Yes)
+        PANIC("Unknown PanicMode: {}", panic_mode);
+
+    return PanicMode::Halt;
+}
+
 UNMAP_AFTER_INIT bool CommandLine::are_framebuffer_devices_enabled() const
 {
     return lookup("fbdev"sv).value_or("on"sv) == "on"sv;

Kernel/CommandLine.h

@@ -22,6 +22,11 @@ enum class BootMode {
     Unknown,
 };
 
+enum class PanicMode {
+    Halt,
+    Shutdown,
+};
+
 enum class HPETMode {
     Periodic,
     NonPeriodic
@@ -70,6 +75,7 @@ public:
     [[nodiscard]] bool is_force_pio() const;
     [[nodiscard]] AcpiFeatureLevel acpi_feature_level() const;
     [[nodiscard]] BootMode boot_mode(Validate should_validate = Validate::No) const;
+    [[nodiscard]] PanicMode panic_mode(Validate should_validate = Validate::No) const;
     [[nodiscard]] HPETMode hpet_mode() const;
     [[nodiscard]] bool disable_physical_storage() const;
     [[nodiscard]] bool disable_ps2_controller() const;

Kernel/Panic.cpp

@@ -33,9 +33,13 @@ void __panic(const char* file, unsigned int line, const char* function)
 
     critical_dmesgln("at {}:{} in {}", file, line, function);
     dump_backtrace(PrintToScreen::Yes);
-    if (kernel_command_line().boot_mode() == BootMode::SelfTest)
+    switch (kernel_command_line().panic_mode()) {
+    case PanicMode::Shutdown:
         __shutdown();
-    else
+    case PanicMode::Halt:
+        [[fallthrough]];
+    default:
         Processor::halt();
+    }
 }
 }

Meta/Azure/Serenity.yml

@@ -80,7 +80,7 @@ jobs:
       timeoutInMinutes: 60
       env:
         SERENITY_QEMU_CPU: 'max,vmx=off'
-        SERENITY_KERNEL_CMDLINE: 'fbdev=off boot_mode=self-test'
+        SERENITY_KERNEL_CMDLINE: 'fbdev=off panic=shutdown boot_mode=self-test'
         SERENITY_RUN: 'ci'
 
     - script: |

Meta/serenity.sh

@@ -358,6 +358,8 @@ if [[ "$CMD" =~ ^(build|install|image|copy-src|run|gdb|test|rebuild|recreate|kad
             else
                 build_target install
                 build_target image
+                # In contrast to CI, we don't set 'panic=shutdown' here,
+                # in case the user wants to inspect qemu some more.
                 export SERENITY_KERNEL_CMDLINE="fbdev=off boot_mode=self-test"
                 export SERENITY_RUN="ci"
                 build_target run