kernel_loader: return a struct for better naming

The new LoadedKernel structure also splits out the size and end address,
which are both used in different places (x86_64 wants end, aarch64 wants
both).

BUG=b:234155022
TEST=tools/presubmit
TEST=cargo test -p kernel_loader

Change-Id: I86a7e412c983f29a2c614cc9e6896aa11db6ba94
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3673611
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>

aarch64/src/lib.rs

@@ -274,8 +274,9 @@ impl arch::LinuxArch for AArch64 {
                             .map_err(Error::KernelLoadFailure)?;
                     kernel_end = get_kernel_addr().offset() + kernel_size as u64;
                 } else {
-                    kernel_end = elf_result.map_err(Error::LoadElfKernel)?;
-                    kernel_size = kernel_end as usize - get_kernel_addr().offset() as usize;
+                    let loaded_kernel = elf_result.map_err(Error::LoadElfKernel)?;
+                    kernel_size = loaded_kernel.size as usize;
+                    kernel_end = loaded_kernel.end.offset();
                 }
                 initrd = match components.initrd_image {
                     Some(initrd_file) => {

kernel_loader/src/lib.rs

@@ -61,6 +61,16 @@ pub enum Error {
 }
 pub type Result<T> = std::result::Result<T, Error>;
 
+#[derive(Debug, Copy, Clone, PartialEq)]
+/// Information about a kernel loaded with the [`load_kernel`] function.
+pub struct LoadedKernel {
+    /// End address (exclusive) of the kernel.
+    pub end: GuestAddress,
+
+    /// Size of the kernel image in bytes.
+    pub size: u64,
+}
+
 /// Loads a kernel from a vmlinux elf image to a slice
 ///
 /// # Arguments
@@ -72,7 +82,7 @@ pub fn load_kernel<F>(
     guest_mem: &GuestMemory,
     kernel_start: GuestAddress,
     mut kernel_image: &mut F,
-) -> Result<u64>
+) -> Result<LoadedKernel>
 where
     F: Read + Seek + AsRawDescriptor,
 {
@@ -135,7 +145,12 @@ where
             .ok_or(Error::InvalidProgramHeaderMemSize)?;
     }
 
-    Ok(kernel_end)
+    let size = kernel_end - kernel_start.offset();
+
+    Ok(LoadedKernel {
+        end: GuestAddress(kernel_end),
+        size,
+    })
 }
 
 /// Writes the command line string to the given memory slice.
@@ -246,7 +261,9 @@ mod test {
         let gm = create_guest_mem();
         let kernel_addr = GuestAddress(0x0);
         let mut image = make_elf_bin();
-        assert_eq!(Ok(0x20_0035), load_kernel(&gm, kernel_addr, &mut image));
+        let kernel = load_kernel(&gm, kernel_addr, &mut image).expect("failed to load ELF");
+        assert_eq!(kernel.end, GuestAddress(0x20_0035));
+        assert_eq!(kernel.size, 0x20_0035);
     }
 
     #[test]

x86_64/src/lib.rs

@@ -1219,8 +1219,8 @@ impl X8664arch {
             bzimage::load_bzimage(mem, GuestAddress(KERNEL_START_OFFSET), kernel_image)
                 .map_err(Error::LoadBzImage)
         } else {
-            let kernel_end = elf_result.map_err(Error::LoadKernel)?;
-            Ok((Default::default(), kernel_end))
+            let loaded_kernel = elf_result.map_err(Error::LoadKernel)?;
+            Ok((Default::default(), loaded_kernel.end.offset()))
         }
     }