From 2c44538f72b063dcfa8dc19a908c7e2fd47c7a4d Mon Sep 17 00:00:00 2001
From: Artemis Tosini <me@artem.ist>
Date: Wed, 31 Jul 2024 21:49:51 +0000
Subject: [PATCH] allocate buffer, don't actually do anything with it

---
 Cargo.lock     | 45 +++++++--------------------------------------
 Cargo.toml     |  2 +-
 src/main.rs    | 37 ++++++++++++++++++++++++++++++++-----
 src/staging.rs | 36 ++++++++++++++++++++++++++++++++++++
 4 files changed, 76 insertions(+), 44 deletions(-)
 create mode 100644 src/staging.rs

diff --git a/Cargo.lock b/Cargo.lock
index 30a555e..7d7c7e2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -20,38 +20,27 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "elf"
+version = "0.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4445909572dbd556c457c849c4ca58623d84b27c8fff1e74b0b4227d8b90d17b"
+
 [[package]]
 name = "freeloader"
 version = "0.1.0"
 dependencies = [
- "goblin",
+ "elf",
  "log",
  "uefi",
 ]
 
-[[package]]
-name = "goblin"
-version = "0.8.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b363a30c165f666402fe6a3024d3bec7ebc898f96a4a23bd1c99f8dbf3f4f47"
-dependencies = [
- "log",
- "plain",
- "scroll",
-]
-
 [[package]]
 name = "log"
 version = "0.4.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
 
-[[package]]
-name = "plain"
-version = "0.2.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b4596b6d070b27117e987119b4dac604f3c58cfb0b191112e24771b2faeac1a6"
-
 [[package]]
 name = "proc-macro2"
 version = "1.0.86"
@@ -90,26 +79,6 @@ dependencies = [
  "proc-macro2",
 ]
 
-[[package]]
-name = "scroll"
-version = "0.12.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6ab8598aa408498679922eff7fa985c25d58a90771bd6be794434c5277eab1a6"
-dependencies = [
- "scroll_derive",
-]
-
-[[package]]
-name = "scroll_derive"
-version = "0.12.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f81c2fde025af7e69b1d1420531c8a8811ca898919db177141a85313b1cb932"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 2.0.72",
-]
-
 [[package]]
 name = "syn"
 version = "1.0.109"
diff --git a/Cargo.toml b/Cargo.toml
index 97badc6..e47be2c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,4 +6,4 @@ edition = "2021"
 [dependencies]
 uefi = { version = "0.29.0", default-features = false, features = [ "alloc", "global_allocator", "panic_handler", "logger" ] }
 log = { version = "0.4.22", default-features = false }
-goblin = { version = "0.8.2", default_features = false, features = [ "elf32", "elf64", "alloc" ] }
+elf = { version = "0.7.4", default_features = false }
diff --git a/src/main.rs b/src/main.rs
index 42591aa..b4dc398 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,14 +2,41 @@
 #![no_std]
 
 mod abi;
+mod staging;
 
+use elf::endian::NativeEndian;
 use log::info;
-use uefi::prelude::*;
+use uefi::{fs::FileSystem, prelude::*};
 
 #[entry]
-fn main(_image_handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
+fn main(image_handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
     uefi::helpers::init(&mut system_table).unwrap();
-    info!("Hello, world!");
-    system_table.boot_services().stall(10_000_000);
-    Status::SUCCESS
+
+    info!("Starting freeloader");
+
+    let staging_buf = staging::allocate_staging(system_table.boot_services());
+
+    let mut esp = FileSystem::new(
+        system_table
+            .boot_services()
+            .get_image_file_system(image_handle)
+            .expect("Failed to get ESP handle"),
+    );
+
+    let kernel = esp
+        .read(cstr16!("efi\\freebsd\\kernel"))
+        .expect("Failed to read kernel");
+
+    info!("Loaded kernel");
+
+    staging_buf[..kernel.len()].copy_from_slice(&kernel);
+
+    let header =
+        elf::ElfBytes::<NativeEndian>::minimal_parse(&staging_buf).expect("Failed to parse kernel");
+
+    info!("Kernel is {:?}", header.ehdr.class);
+
+    loop {
+        system_table.boot_services().stall(10_000_000);
+    }
 }
diff --git a/src/staging.rs b/src/staging.rs
new file mode 100644
index 0000000..3ff8ccc
--- /dev/null
+++ b/src/staging.rs
@@ -0,0 +1,36 @@
+use log::info;
+use uefi::table::boot::{AllocateType, BootServices, MemoryType};
+
+/// Size of the staging buffer for preloaded files
+const STAGING_BUF_SIZE: usize = 64 * 1024 * 1024;
+const STAGING_BUF_NUM_PAGES: usize = STAGING_BUF_SIZE / uefi::table::boot::PAGE_SIZE;
+
+const ADDR_ROUND: u64 = 2 * 1024 * 1024;
+
+pub fn allocate_staging(boot_services: &BootServices) -> &'static mut [u8] {
+    let allocation_type = if cfg!(target_arch = "x86_64") {
+        // Must be under 4GiB because we need to pass a 32-bit pointer
+        AllocateType::MaxAddress(4 * 1024 * 1024 * 1024)
+    } else {
+        AllocateType::AnyPages
+    };
+
+    let base = boot_services
+        .allocate_pages(
+            allocation_type,
+            MemoryType::LOADER_CODE,
+            STAGING_BUF_NUM_PAGES,
+        )
+        .expect("Unable to allocate staging area");
+
+    // Some architectures want a kernel on a 2MiB boundary, do it everywhere
+    let rounded = ((base + ADDR_ROUND - 1) / ADDR_ROUND) * ADDR_ROUND;
+
+    let available_size = STAGING_BUF_SIZE - ((rounded - base) as usize);
+    info!(
+        "Allocated {:#018x} byte staging buffer at {:#018x}",
+        available_size, rounded
+    );
+
+    unsafe { core::slice::from_raw_parts_mut(rounded as *mut u8, available_size) }
+}