From 0673ef9b42c189b25b93da7d543950290faf4146 Mon Sep 17 00:00:00 2001
From: Hiroki Tokunaga <tokusan441@gmail.com>
Date: Sat, 26 Jun 2021 16:58:19 +0900
Subject: [PATCH] feat(bootx64): jump to the kernel (#81)

---
 bootloader/bootx64/src/elf.rs    |  9 +++++++--
 bootloader/bootx64/src/main.rs   | 13 ++++++++-----
 bootloader/bootx64/src/paging.rs |  5 +++--
 kernel/src/main.rs               |  4 +++-
 4 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/bootloader/bootx64/src/elf.rs b/bootloader/bootx64/src/elf.rs
index 97492fee..9a798ecd 100644
--- a/bootloader/bootx64/src/elf.rs
+++ b/bootloader/bootx64/src/elf.rs
@@ -19,7 +19,7 @@ use x86_64::VirtAddr;
 /// The caller must ensure that
 /// - The recursive paging address `0xff7f_bfdf_e000` is accessible.
 /// - There is no reference to one of the all working page tables.
-pub unsafe fn load(binary: &[u8], mmap: &mut [MemoryDescriptor]) {
+pub unsafe fn load(binary: &[u8], mmap: &mut [MemoryDescriptor]) -> VirtAddr {
     // SAFETY: The all rules are satisfied.
     paging::edit_page_tables(|| unsafe { load_without_disabling_page_table_protects(binary, mmap) })
 }
@@ -29,7 +29,10 @@ pub unsafe fn load(binary: &[u8], mmap: &mut [MemoryDescriptor]) {
 /// The caller must ensure that
 /// - The recursive paging address `0xff7f_bfdf_e000` is accessible.
 /// - There is no reference to one of the all working page tables.
-unsafe fn load_without_disabling_page_table_protects(binary: &[u8], mmap: &mut [MemoryDescriptor]) {
+unsafe fn load_without_disabling_page_table_protects(
+    binary: &[u8],
+    mmap: &mut [MemoryDescriptor],
+) -> VirtAddr {
     let mut allocator = Allocator::new(mmap);
 
     // SAFETY: The caller ensures that the recursive paging is enabled and there is no reference to
@@ -43,6 +46,8 @@ unsafe fn load_without_disabling_page_table_protects(binary: &[u8], mmap: &mut [
 
     let r = elf.load(&mut loader);
     r.expect("Failed to load a ELF file.");
+
+    VirtAddr::new(elf.entry_point())
 }
 
 struct Loader<'a> {
diff --git a/bootloader/bootx64/src/main.rs b/bootloader/bootx64/src/main.rs
index bcabf288..8bf92470 100644
--- a/bootloader/bootx64/src/main.rs
+++ b/bootloader/bootx64/src/main.rs
@@ -11,7 +11,7 @@ use bootx64::paging;
 use bootx64::{fs, uefi_println};
 
 #[no_mangle]
-pub extern "win64" fn efi_main(h: uefi_wrapper::Handle, mut st: bootx64::SystemTable) -> ! {
+extern "win64" fn efi_main(h: uefi_wrapper::Handle, mut st: bootx64::SystemTable) -> ! {
     let resolution = gop::set_preferred_resolution(&mut st);
     uefi_println!(&mut st, "GOP info: {:?}", resolution);
 
@@ -24,9 +24,12 @@ pub extern "win64" fn efi_main(h: uefi_wrapper::Handle, mut st: bootx64::SystemT
     unsafe { paging::enable_recursive_paging() };
 
     // SAFETY: Yes, the recursive paging is enabled and there are no references to the PML4.
-    unsafe { elf::load(bytes, mmap) };
+    let entry = unsafe { elf::load(bytes, mmap) };
+    assert!(!entry.is_null(), "The entry address is null.");
 
-    loop {
-        x86_64::instructions::hlt();
-    }
+    // SAFETY: Safe as described in
+    // https://rust-lang.github.io/unsafe-code-guidelines/layout/function-pointers.html#representation.
+    let entry: fn() -> ! = unsafe { core::mem::transmute(entry) };
+
+    (entry)()
 }
diff --git a/bootloader/bootx64/src/paging.rs b/bootloader/bootx64/src/paging.rs
index 1fa1726b..0dfff039 100644
--- a/bootloader/bootx64/src/paging.rs
+++ b/bootloader/bootx64/src/paging.rs
@@ -5,10 +5,11 @@ use x86_64::structures::paging::PageTableFlags;
 use x86_64::PhysAddr;
 use x86_64::VirtAddr;
 
-pub(crate) fn edit_page_tables(f: impl FnOnce()) {
+pub(crate) fn edit_page_tables<T>(f: impl FnOnce() -> T) -> T {
     disable_write_protect();
-    f();
+    let r = f();
     enable_write_protect();
+    r
 }
 
 /// # Safety
diff --git a/kernel/src/main.rs b/kernel/src/main.rs
index 365a8dbc..5849fd5c 100644
--- a/kernel/src/main.rs
+++ b/kernel/src/main.rs
@@ -7,6 +7,8 @@ extern crate kernel as _;
 #[no_mangle]
 fn main() {
     unsafe {
-        *(0x334 as *mut u8) = 3_u8;
+        loop {
+            *(0x334 as *mut u8) = 3_u8;
+        }
     }
 }