Let auto splitters hand in the Unity runtime module (#174)

src/game_engine/unity/il2cpp/mod.rs

@@ -86,6 +86,25 @@ impl Module {
         Self::attach_with(process, il2cpp_module, format, profile)
     }
 
+    /// Tries attaching to a Unity game that is using the IL2CPP backend, in
+    /// the module at `il2cpp_module`, with the provided measured [`Profile`].
+    /// Use this when the runtime sits in a module [`attach`](Self::attach)
+    /// doesn't look for, such as a renamed `GameAssembly.dll`.
+    /// [`Process::get_module_address`] finds a module by its name without
+    /// allocating. The module must be a PE or an ELF image whose pointer width
+    /// matches the profile.
+    pub fn attach_to_module(
+        process: &Process,
+        il2cpp_module: Address,
+        profile: Profile,
+    ) -> Option<Self> {
+        let (il2cpp_module, format) = super::module_at(process, il2cpp_module)?;
+        let pointer_size = Self::pointer_size(process, il2cpp_module, format)?;
+        (pointer_size == profile.pointer_size).then_some(())?;
+
+        Self::attach_with(process, il2cpp_module, format, profile)
+    }
+
     /// Finds the module the runtime is compiled into, which is
     /// `GameAssembly.dll` on Windows and `GameAssembly.so` on Linux.
     fn find_runtime_module(process: &Process) -> Option<((Address, u64), BinaryFormat)> {
@@ -480,6 +499,20 @@ impl Module {
         retry(|| Self::attach(process, profile)).await
     }
 
+    /// Attaches to a Unity game that is using the IL2CPP backend, in the
+    /// module at `il2cpp_module`, with the provided measured [`Profile`].
+    ///
+    /// This is the `await`able version of
+    /// [`attach_to_module`](Self::attach_to_module), yielding back to the
+    /// runtime between each try.
+    pub async fn wait_attach_to_module(
+        process: &Process,
+        il2cpp_module: Address,
+        profile: Profile,
+    ) -> Module {
+        retry(|| Self::attach_to_module(process, il2cpp_module, profile)).await
+    }
+
     /// Looks for the specified binary [image](Image) inside the target process.
     /// An [image](Image) is a .NET DLL that is loaded
     /// by the game. The `Assembly-CSharp` [image](Image) is the main game

src/game_engine/unity/il2cpp/walk_tests.rs

@@ -220,6 +220,30 @@ fn attach_auto_detect_uses_a_measured_build() {
     assert_eq!(module.profile.class.static_fields, 0xA0);
 }
 
+// A runtime under a file name `attach` doesn't look for still attaches
+// through the module the auto splitter hands in. An address that holds no
+// module doesn't attach.
+#[test]
+fn a_given_module_attaches_under_any_name() {
+    let image = Player::game_assembly();
+    with_modules(
+        &[(GAME_ASSEMBLY, &image)],
+        &[("GameAssembly_x64.dll", GAME_ASSEMBLY, 0x1000)],
+        |process| {
+            let profile = super::profiles::UNITY_6000_5_0F1_X86_64;
+            assert!(Module::attach(process, profile).is_none());
+            let module = process.get_module_address("GameAssembly_x64.dll").unwrap();
+            let attached = Module::attach_to_module(process, module, profile).unwrap();
+            assert_eq!(attached.profile, profile);
+            assert!(Module::attach_to_module(process, module + 0x800, profile).is_none());
+            assert!(matches!(
+                poll_once(Module::wait_attach_to_module(process, module, profile)),
+                Poll::Ready(_)
+            ));
+        },
+    );
+}
+
 #[test]
 fn attach_uses_the_explicit_profile_and_checks_its_width() {
     let player = Player {

src/game_engine/unity/mod.rs

@@ -89,7 +89,14 @@ pub use managed::{DictionaryOffsets, HashSetOffsets, ListOffsets, ManagedString}
 pub mod mono;
 pub mod scene_manager;
 
-use crate::{signature::Signature, Address, Process};
+#[cfg(all(test, not(target_family = "wasm")))]
+mod module_tests;
+
+use crate::{
+    file_format::{elf, pe},
+    signature::Signature,
+    Address, Process,
+};
 
 const CSTR: usize = 128;
 
@@ -102,6 +109,19 @@ enum BinaryFormat {
     MachO,
 }
 
+/// Reads the format and the size of the module at `address` from its
+/// header. A PE image spans the size of image its optional header gives and
+/// an ELF image runs to the end of its last load segment. asr has no reader
+/// for a Mach-O image's size, so a Mach-O image gives `None` like any header
+/// it doesn't know.
+fn module_at(process: &Process, address: Address) -> Option<((Address, u64), BinaryFormat)> {
+    if let Some(size) = pe::read_size_of_image(process, address) {
+        return Some(((address, size as u64), BinaryFormat::PE));
+    }
+    let size = elf::read_size_of_image(process, address)?;
+    Some(((address, size), BinaryFormat::ELF))
+}
+
 /// Finds the Unity version string in a player, `2021.3.11f1` for
 /// example, and returns its three numbers. The fourth part of a file
 /// version has no equal in the string, so it is 0. A NUL heads the

src/game_engine/unity/module_tests.rs

@@ -0,0 +1,61 @@
+//! Tests reading a module's format and size from its header, for auto
+//! splitters that hand in the module themselves.
+
+use super::{module_at, BinaryFormat};
+use crate::{runtime::mock::with_process, Address};
+
+use std::vec;
+
+const BASE: u64 = 0x7FF6_1000_0000;
+
+fn put(image: &mut [u8], at: usize, bytes: &[u8]) {
+    image[at..at + bytes.len()].copy_from_slice(bytes);
+}
+
+#[test]
+fn pe_module_spans_its_size_of_image() {
+    // The DOS header points at the COFF header, which is followed by a PE32+
+    // optional header that says the image is 0x5000 bytes.
+    let mut image = vec![0; 0x400];
+    put(&mut image, 0, b"MZ");
+    put(&mut image, 0x3C, &0x80_u32.to_le_bytes());
+    put(&mut image, 0x80, b"PE\0\0");
+    put(&mut image, 0x84, &0x8664_u16.to_le_bytes());
+    put(&mut image, 0x94, &0xF0_u16.to_le_bytes());
+    put(&mut image, 0x98, &0x20B_u16.to_le_bytes());
+    put(&mut image, 0x98 + 0x38, &0x5000_u32.to_le_bytes());
+    with_process(&[(BASE, &image)], |process| {
+        assert_eq!(
+            module_at(process, Address::new(BASE)),
+            Some(((Address::new(BASE), 0x5000), BinaryFormat::PE))
+        );
+    });
+}
+
+#[test]
+fn elf_module_spans_to_its_last_load_segment() {
+    // An ELF64 header with one program header, a load segment that runs to
+    // 0x3000 in memory.
+    let mut image = vec![0; 0x400];
+    put(&mut image, 0, b"\x7fELF\x02\x01\x01");
+    put(&mut image, 0x10, &3_u16.to_le_bytes());
+    put(&mut image, 0x20, &0x40_u64.to_le_bytes());
+    put(&mut image, 0x36, &56_u16.to_le_bytes());
+    put(&mut image, 0x38, &1_u16.to_le_bytes());
+    put(&mut image, 0x40, &1_u32.to_le_bytes());
+    put(&mut image, 0x68, &0x3000_u64.to_le_bytes());
+    with_process(&[(BASE, &image)], |process| {
+        assert_eq!(
+            module_at(process, Address::new(BASE)),
+            Some(((Address::new(BASE), 0x3000), BinaryFormat::ELF))
+        );
+    });
+}
+
+#[test]
+fn unknown_header_gives_no_module() {
+    let image = vec![0; 0x400];
+    with_process(&[(BASE, &image)], |process| {
+        assert_eq!(module_at(process, Address::new(BASE)), None);
+    });
+}

src/game_engine/unity/mono/attachment_tests.rs

@@ -111,3 +111,29 @@ fn an_unknown_legacy_runtime_uses_the_executables_version() {
         },
     );
 }
+
+// A runtime under a file name `attach` doesn't look for still attaches
+// through the module the auto splitter hands in, which doesn't need `alloc`.
+// An address that holds no module doesn't attach.
+#[test]
+fn a_given_module_attaches_under_any_name() {
+    let runtime = runtime();
+    with_modules(
+        &[(RUNTIME, &runtime)],
+        &[("libmono-game.so", RUNTIME, runtime.len() as u64)],
+        |process| {
+            let profile = profiles::UNITY_5_6_0F1_LINUX_MONO_X86_64;
+            assert!(Module::attach(process, profile).is_none());
+            let module = process.get_module_address("libmono-game.so").unwrap();
+            let attached = Module::attach_to_module(process, module, profile).unwrap();
+            assert_eq!(attached.profile, profile);
+            assert!(Module::attach_to_module(process, module + 0x1000, profile).is_none());
+            let Poll::Ready(attached) =
+                poll_once(Module::wait_attach_to_module(process, module, profile))
+            else {
+                panic!("the given module should attach immediately");
+            };
+            assert_eq!(attached.profile, profile);
+        },
+    );
+}

src/game_engine/unity/mono/mod.rs

@@ -5,7 +5,9 @@
 //! a separate player module can be identified through its executable. A
 //! `no_std` auto splitter using allocation must provide a global allocator. Use
 //! [`Module::attach`] or [`Module::wait_attach`] with a known [`Profile`] to
-//! attach without allocation on Windows and Linux. macOS support requires
+//! attach without allocation on Windows and Linux.
+//! [`Module::attach_to_module`] does the same for a runtime the auto splitter
+//! finds itself. macOS support requires
 //! `alloc` for Mach-O symbol lookup even with an explicit profile.
 
 #[cfg(feature = "alloc")]
@@ -228,6 +230,28 @@ impl Module {
         Self::attach_with(process, module_range, format, profile)
     }
 
+    /// Tries attaching to a Unity game that is using the standard Mono
+    /// backend, in the module at `mono_module`, with the provided measured
+    /// [`Profile`]. Use this when the runtime sits in a module
+    /// [`attach`](Self::attach) doesn't look for, such as a renamed runtime
+    /// library. [`Process::get_module_address`] finds a module by its name
+    /// without allocating. The module must be a PE or an ELF image whose
+    /// pointer width matches the profile and the profile's library must be
+    /// the runtime the module holds.
+    pub fn attach_to_module(
+        process: &Process,
+        mono_module: Address,
+        profile: Profile,
+    ) -> Option<Self> {
+        let (module_range, format) = super::module_at(process, mono_module)?;
+        let pointer_size = Self::pointer_size(process, module_range, format)?;
+        if pointer_size != profile.pointer_size {
+            return None;
+        }
+
+        Self::attach_with(process, module_range, format, profile)
+    }
+
     fn find_runtime_module(
         process: &Process,
     ) -> Option<((Address, u64), BinaryFormat, &'static str, Library)> {
@@ -739,6 +763,20 @@ impl Module {
         retry(|| Self::attach(process, profile)).await
     }
 
+    /// Attaches to a Unity game that is using the standard Mono backend, in
+    /// the module at `mono_module`, with the provided measured [`Profile`].
+    ///
+    /// This is the `await`able version of
+    /// [`attach_to_module`](Self::attach_to_module), yielding back to the
+    /// runtime between each try.
+    pub async fn wait_attach_to_module(
+        process: &Process,
+        mono_module: Address,
+        profile: Profile,
+    ) -> Self {
+        retry(|| Self::attach_to_module(process, mono_module, profile)).await
+    }
+
     /// Looks for the specified binary [image](Image) inside the target process.
     /// An [image](Image) is a .NET DLL that is loaded
     /// by the game. The `Assembly-CSharp` [image](Image) is the main game