uefi: Drop duplicate global system table pointer

Now that `uefi::table` has a pointer to the system table, drop the pointer from
`uefi::helpers`.

Author: nicholasbishop

uefi/src/helpers/mod.rs

@@ -19,14 +19,9 @@
 //! [println_macro]: uefi::println!
 
 use crate::prelude::{Boot, SystemTable};
-use crate::Result;
-use crate::StatusExt;
-use core::ffi::c_void;
-use core::ptr;
-use core::sync::atomic::{AtomicPtr, Ordering};
+use crate::{table, Result};
 #[doc(hidden)]
 pub use println::_print;
-use uefi_raw::Status;
 
 #[cfg(feature = "global_allocator")]
 mod global_allocator;
@@ -36,25 +31,6 @@ mod logger;
 mod panic_handler;
 mod println;
 
-/// Reference to the system table.
-///
-/// This table is only fully safe to use until UEFI boot services have been exited.
-/// After that, some fields and methods are unsafe to use, see the documentation of
-/// UEFI's ExitBootServices entry point for more details.
-static SYSTEM_TABLE: AtomicPtr<c_void> = AtomicPtr::new(core::ptr::null_mut());
-
-#[must_use]
-fn system_table_opt() -> Option<SystemTable<Boot>> {
-    let ptr = SYSTEM_TABLE.load(Ordering::Acquire);
-    // Safety: the `SYSTEM_TABLE` pointer either be null or a valid system
-    // table.
-    //
-    // Null is the initial value, as well as the value set when exiting boot
-    // services. Otherwise, the value is set by the call to `init`, which
-    // requires a valid system table reference as input.
-    unsafe { SystemTable::from_ptr(ptr) }
-}
-
 /// Obtains a pointer to the system table.
 ///
 /// This is meant to be used by higher-level libraries,
@@ -66,7 +42,7 @@ fn system_table_opt() -> Option<SystemTable<Boot>> {
 #[must_use]
 // TODO do we want to keep this public?
 pub fn system_table() -> SystemTable<Boot> {
-    system_table_opt().expect("The system table handle is not available")
+    table::system_table_boot().expect("boot services are not active")
 }
 
 /// Initialize all helpers defined in [`uefi::helpers`] whose Cargo features
@@ -78,15 +54,8 @@ pub fn system_table() -> SystemTable<Boot> {
 /// **PLEASE NOTE** that these helpers are meant for the pre exit boot service
 /// epoch. Limited functionality might work after exiting them, such as logging
 /// to the debugcon device.
+#[allow(unused_variables)] // `st` is unused if logger and allocator are disabled
 pub fn init(st: &mut SystemTable<Boot>) -> Result<()> {
-    if system_table_opt().is_some() {
-        // Avoid double initialization.
-        return Status::SUCCESS.to_result_with_val(|| ());
-    }
-
-    // Setup the system table singleton
-    SYSTEM_TABLE.store(st.as_ptr().cast_mut(), Ordering::Release);
-
     // Setup logging and memory allocation
 
     #[cfg(feature = "logger")]
@@ -103,14 +72,6 @@ pub fn init(st: &mut SystemTable<Boot>) -> Result<()> {
 }
 
 pub(crate) fn exit() {
-    // DEBUG: The UEFI spec does not guarantee that this printout will work, as
-    //        the services used by logging might already have been shut down.
-    //        But it works on current OVMF, and can be used as a handy way to
-    //        check that the callback does get called.
-    //
-    // info!("Shutting down the UEFI utility library");
-    SYSTEM_TABLE.store(ptr::null_mut(), Ordering::Release);
-
     #[cfg(feature = "logger")]
     logger::disable();
 

uefi/src/helpers/panic_handler.rs

@@ -1,13 +1,13 @@
-use crate::helpers::system_table_opt;
 use crate::println;
+use crate::table::system_table_boot;
 use cfg_if::cfg_if;
 
 #[panic_handler]
 fn panic_handler(info: &core::panic::PanicInfo) -> ! {
     println!("[PANIC]: {}", info);
 
     // Give the user some time to read the message
-    if let Some(st) = system_table_opt() {
+    if let Some(st) = system_table_boot() {
         st.boot_services().stall(10_000_000);
     } else {
         let mut dummy = 0u64;
@@ -28,7 +28,7 @@ fn panic_handler(info: &core::panic::PanicInfo) -> ! {
             qemu_exit_handle.exit_failure();
         } else {
             // If the system table is available, use UEFI's standard shutdown mechanism
-            if let Some(st) = system_table_opt() {
+            if let Some(st) = system_table_boot() {
                 use crate::table::runtime::ResetType;
                 st.runtime_services()
                     .reset(ResetType::SHUTDOWN, crate::Status::ABORTED, None);

uefi/src/helpers/println.rs

@@ -1,10 +1,11 @@
-use crate::helpers::system_table;
+use crate::table::system_table_boot;
 use core::fmt::Write;
 
 /// INTERNAL API! Helper for print macros.
 #[doc(hidden)]
 pub fn _print(args: core::fmt::Arguments) {
-    system_table()
+    system_table_boot()
+        .expect("boot services are not active")
         .stdout()
         .write_fmt(args)
         .expect("Failed to write to stdout");