uef-raw: add MemoryDescriptor::uefi_desc_size()

This helps to create unit tests for the memory map which are closer to a real
world scenario.

Author: phip1611

uefi-raw/CHANGELOG.md

@@ -1,5 +1,8 @@
 # uefi-raw - [Unreleased]
 
+## Added
+- `MemoryDescriptor::uefi_desc_size`
+
 ## Changed
 - `maximum_capsule_size` of `query_capsule_capabilities` now takes a *mut u64 instead of a *mut usize.
 - `ResetType` now derives the `Default` trait.

uefi-raw/src/table/boot.rs

@@ -5,6 +5,7 @@ use crate::table::Header;
 use crate::{Char16, Event, Guid, Handle, PhysicalAddress, Status, VirtualAddress};
 use bitflags::bitflags;
 use core::ffi::c_void;
+use core::mem;
 
 /// Table of pointers to all the boot services.
 #[derive(Debug)]
@@ -363,6 +364,25 @@ pub struct MemoryDescriptor {
 impl MemoryDescriptor {
     /// Memory descriptor version number.
     pub const VERSION: u32 = 1;
+
+    /// Returns a best-effort **guess** of the `desc_size` that UEFI will
+    /// report for a [`MemoryDescriptor`]. You may use this in unit testing. In
+    /// integration tests and real world scenarios, refrain from using this, and
+    /// use the actual reported `desc_size` reported from `UEFI#GetMemoryMap()`
+    /// instead.
+    ///
+    /// # Safety
+    /// Unsafe because you should always use the `desc_size` that is associated
+    /// with the memory map.
+    #[must_use]
+    pub const unsafe fn uefi_desc_size() -> usize {
+        let size_base = mem::size_of::<Self>();
+        // Taken from https://github.com/tianocore/edk2/blob/7142e648416ff5d3eac6c6d607874805f5de0ca8/MdeModulePkg/Core/PiSmmCore/Page.c#L1059
+        let desc_size_diff = mem::size_of::<u64>() - size_base % mem::size_of::<u64>();
+        let desc_size = size_base + desc_size_diff;
+        assert!(desc_size > size_base);
+        desc_size
+    }
 }
 
 impl Default for MemoryDescriptor {
@@ -466,3 +486,17 @@ pub enum Tpl: usize => {
     /// Even processor interrupts are disable at this level.
     HIGH_LEVEL  = 31,
 }}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// This refers to the ABI of the MemoryDescriptor version 1 a
+    #[test]
+    fn test_abi_v1() {
+        assert_eq!(MemoryDescriptor::VERSION, 1);
+        assert_eq!(mem::size_of::<MemoryDescriptor>(), 40);
+        // This is what GetMemoryMap from UEFI usually returns.
+        assert_eq!(unsafe { MemoryDescriptor::uefi_desc_size() }, 48);
+    }
+}