Overhaul Dealing with UEFI ZSTs

A complete rewrite of VariableSizeType wrapper to match the
semantics of Box.

This commit is a part of a series of commits to clean up the
`std::os::uefi` namespace.

Signed-off-by: Ayush <ayushsingh1325@gmail.com>

Author: Ayush1325

library/std/src/lib.rs

@@ -243,8 +243,10 @@
 #![feature(c_unwind)]
 #![feature(cfg_target_thread_local)]
 #![feature(concat_idents)]
+#![feature(const_deref)]
 #![feature(const_mut_refs)]
 #![feature(const_trait_impl)]
+#![feature(const_try)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
 #![feature(doc_cfg)]
@@ -309,6 +311,7 @@
 #![feature(prelude_2024)]
 #![feature(provide_any)]
 #![feature(ptr_as_uninit)]
+#![feature(ptr_internals)]
 #![feature(raw_os_nonzero)]
 #![feature(slice_internals)]
 #![feature(slice_ptr_get)]
@@ -323,6 +326,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(get_mut_unchecked)]
+#![feature(const_alloc_error)]
 #![feature(map_try_insert)]
 #![feature(new_uninit)]
 #![feature(thin_box)]

library/std/src/os/uefi/mod.rs

@@ -6,5 +6,4 @@ pub mod env;
 pub mod ffi;
 pub mod io;
 pub mod net;
-pub mod path;
 pub mod raw;

library/std/src/os/uefi/path.rs

@@ -1,63 +1,3 @@
 //! This module just re-exports stuff from r-efi crate
 
 pub use r_efi::efi::{BootServices, Guid, RuntimeServices, SystemTable};
-
-use crate::alloc::{Allocator, Global, Layout};
-use crate::io;
-use crate::ptr::NonNull;
-use crate::sys_common::AsInner;
-
-// A type to make working with Variable Sized Types easier
-pub(crate) struct VariableSizeType<T> {
-    inner: NonNull<T>,
-    layout: Layout,
-}
-
-impl<T> VariableSizeType<T> {
-    const ALIGNMENT: usize = 8;
-
-    pub(crate) fn new(inner: NonNull<T>, layout: Layout) -> Self {
-        Self { inner, layout }
-    }
-
-    pub(crate) fn from_size(size: usize) -> io::Result<Self> {
-        let layout = Layout::from_size_align(size, Self::ALIGNMENT).map_err(|_| {
-            io::error::const_io_error!(io::ErrorKind::Uncategorized, "Invalid buffer size")
-        })?;
-        let inner: NonNull<T> = Global
-            .allocate(layout)
-            .map_err(|_| {
-                io::error::const_io_error!(
-                    io::ErrorKind::Uncategorized,
-                    "Failed to allocate Buffer"
-                )
-            })?
-            .cast();
-        Ok(Self::new(inner, layout))
-    }
-
-    pub(crate) fn as_ptr(&self) -> *mut T {
-        self.inner.as_ptr()
-    }
-
-    // Callers responsibility to ensure that it has been inintialized beforehand
-    pub(crate) fn as_ref(&self) -> &T {
-        unsafe { self.inner.as_ref() }
-    }
-
-    pub(crate) fn size(&self) -> usize {
-        self.layout.size()
-    }
-}
-
-impl<T> AsInner<NonNull<T>> for VariableSizeType<T> {
-    fn as_inner(&self) -> &NonNull<T> {
-        &self.inner
-    }
-}
-
-impl<T> Drop for VariableSizeType<T> {
-    fn drop(&mut self) {
-        unsafe { Global.deallocate(self.inner.cast(), self.layout) }
-    }
-}

library/std/src/os/uefi/raw.rs

@@ -5,7 +5,7 @@
 use crate::alloc::{GlobalAlloc, Layout, System};
 use crate::os::uefi;
 
-const POOL_ALIGNMENT: usize = 8;
+pub(crate) const POOL_ALIGNMENT: usize = 8;
 // FIXME: Maybe allow chaing the MEMORY_TYPE. However, since allocation is done even before main,
 // there will be a few allocations with the default MEMORY_TYPE.
 const MEMORY_TYPE: u32 = r_efi::efi::LOADER_DATA;