From ba667148af04963f5d70c647511ea1fad1add21d Mon Sep 17 00:00:00 2001
From: salmonik <salmonik@tuta.io>
Date: Fri, 31 Jul 2026 16:01:46 +0200
Subject: power: proper shutdown via UEFI ResetSystem (ACPI S5)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- uefi.rs: full EFI_RUNTIME_SERVICES layout with reset_system at index 10
  (spec order); EfiResetSystem type + RESET_* constants
- power.rs: stash the runtime-services table pre-EBS; poweroff() calls
  ResetSystem(EfiResetShutdown) — still callable after ExitBootServices
  because we never call SetVirtualAddressMap, so the pointers keep
  working with physical addresses; falls back to the hlt loop
- shell: 'poweroff' and 'exit' shut the machine down (QEMU exits),
  'halt' keeps the plain hlt loop
---
 rsnix/src/power.rs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 rsnix/src/power.rs

(limited to 'rsnix/src/power.rs')

diff --git a/rsnix/src/power.rs b/rsnix/src/power.rs
new file mode 100644
index 0000000..cb5d296
--- /dev/null
+++ b/rsnix/src/power.rs
@@ -0,0 +1,48 @@
+// ---------------------------------------------------------------------------
+// Power — halt loop and ACPI shutdown via the UEFI ResetSystem runtime
+// service.
+//
+// The firmware's runtime-services table is stashed before ExitBootServices
+// (`init`).  Because we never call SetVirtualAddressMap, the service
+// pointers keep working with physical (identity) addresses after EBS, so
+// poweroff() can ask the firmware to shut the machine down (ACPI S5) — on
+// QEMU this makes the VM exit, on real hardware the power drops.
+// ---------------------------------------------------------------------------
+
+use crate::uefi::{RuntimeServices, EFI_SUCCESS, RESET_SHUTDOWN};
+
+static mut RUNTIME_SERVICES: *mut RuntimeServices = core::ptr::null_mut();
+
+/// Stash the runtime-services table pointer (call in Phase 1, pre-EBS).
+pub fn init(rt: *mut RuntimeServices) {
+    unsafe {
+        RUNTIME_SERVICES = rt;
+    }
+}
+
+/// Halt the CPU forever (interrupts off, hlt loop).
+pub fn halt() -> ! {
+    loop {
+        unsafe {
+            core::arch::asm!("cli; hlt", options(nomem, nostack));
+        }
+    }
+}
+
+/// Shut the machine down through `ResetSystem(EfiResetShutdown)`.  Falls
+/// back to `halt()` if no table was saved or the call failed.
+pub fn poweroff() -> ! {
+    unsafe {
+        let rt = RUNTIME_SERVICES;
+        if rt.is_null() {
+            halt();
+        }
+        let reset = (*rt).reset_system;
+        if reset as usize == 0 {
+            halt();
+        }
+        (reset)(RESET_SHUTDOWN, EFI_SUCCESS, 0, core::ptr::null());
+        // ResetSystem only returns on failure.
+        halt()
+    }
+}
-- 
cgit v1.2.3