Merge pull request #280 from rust-osdev/deserialize-errors

Add basic error strings for deserialization errors

Author: phil-opp

README.md

@@ -12,6 +12,12 @@ You need a nightly [Rust](https://www.rust-lang.org) compiler with the `llvm-too
 
 ## Usage
 
+To use this crate, you need to adjust your kernel to be bootable first. Then you can create a bootable disk image from your compiled kernel. These steps are explained in detail below.
+
+If you're already using an older version of the `bootloader` crate, follow our [migration guides](doc/migration).
+
+### Kernel
+
 To make your kernel compatible with `bootloader`:
 
 - Add a dependency on the `bootloader_api` crate in your kernel's `Cargo.toml`.
@@ -29,24 +35,37 @@ To make your kernel compatible with `bootloader`:
     };
     bootloader_api::entry_point!(kernel_main, config = &CONFIG);
     ```
-- Compile your kernel as normal to an ELF executable. The executable will contain a special section with metadata and the serialized config, which will enable the `bootloader` crate to load it.
+- Compile your kernel to an ELF executable by running **`cargo build --target x86_64-unknown-none`**. You might need to run `rustup target add x86_64-unknown-none` before to download precompiled versions of the `core` and `alloc` crates.
+- Thanks to the `entry_point` macro, the compiled executable contains a special section with metadata and the serialized config, which will enable the `bootloader` crate to load it.
+
+### Booting
 
 To combine your kernel with a bootloader and create a bootable disk image, follow these steps:
 
-- Create a new runner crate, e.g. through `cargo new runner --bin`.
-- Add the `bootloader` crate as a `dependency` in the `runner/Cargo.toml`.
-- In the `main.rs`, invoke the build commands for your kernel.
-  - Alternatively, you can set up an [artifact dependency](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies) on your kernel, provided that you use a `rustup`-supported target for your kernel:
-    ```toml
-    [dependencies]
-    my-kernel = { path = "..", artifact = "bin", target = "x86_64-unknown-none" }
-    ```
-- After building your kernel, obtain the path to the kernel executable.
-  - When using an artifact dependency, you can retrieve this path using `env!("CARGO_BIN_FILE_MY_KERNEL_my-kernel")`
-- Use the `bootloader::create_boot_partition` function to create a bootable FAT partition at some chosen path.
-- Use one or multiple `bootloader::create_*_disk_image` functions to transform the bootable FAT partition into a disk image.
-  - Use the `bootloader::create_uefi_disk_image` function to create an UEFI-compatible GPT-formatted disk image.
-  - Use the `bootloader::create_bios_disk_image` function to create a BIOS-compatible MBR-formatted disk image.
+- Move your full kernel code into a `kernel` subdirectory.
+- Create a new `os` crate at the top level that defines a [workspace](https://doc.rust-lang.org/cargo/reference/workspaces.html).
+- Add a `build-dependencies` on the `bootloader` crate.
+- Create a [`build.rs`](https://doc.rust-lang.org/cargo/reference/build-scripts.html) build script.
+- Set up an [artifact dependency](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies) to add your `kernel` crate as a `build-dependency`:
+  ```toml
+  # in Cargo.toml
+  [build-dependencies]
+  kernel = { path = "kernel", artifact = "bin", target = "x86_64-unknown-none" }
+  ```
+  ```toml
+  # .cargo/config.toml
+
+  [unstable]
+  # enable the unstable artifact-dependencies feature, see
+  # https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies
+  bindeps = true
+  ```
+  Alternatively, you can use [`std::process::Command`](https://doc.rust-lang.org/stable/std/process/struct.Command.html) to invoke the build command of your kernel in the `build.rs` script. 
+- Obtain the path to the kernel executable. When using an artifact dependency, you can retrieve this path using `env!("CARGO_BIN_FILE_MY_KERNEL_my-kernel")`
+- Use `bootloader::UefiBoot` and/or `bootloader::BiosBoot` to create a bootable disk image with your kernel.
+- Do something with the bootable disk images in your `main.rs` function. For example, run them with QEMU.
+
+See our [disk image creation template](doc/create-disk-image.md) for a more detailed example.
 
 ## Architecture
 

api/src/config.rs

@@ -149,16 +149,16 @@ impl BootloaderConfig {
     /// ELF file.
     ///
     /// TODO: return error enum
-    pub fn deserialize(serialized: &[u8]) -> Result<Self, ()> {
+    pub fn deserialize(serialized: &[u8]) -> Result<Self, &'static str> {
         if serialized.len() != Self::SERIALIZED_LEN {
-            return Err(());
+            return Err("invalid len");
         }
 
         let s = serialized;
 
         let (uuid, s) = split_array_ref(s);
         if uuid != &Self::UUID {
-            return Err(());
+            return Err("invalid UUID");
         }
 
         let (version, s) = {
@@ -169,7 +169,7 @@ impl BootloaderConfig {
             let pre = match pre {
                 [0] => false,
                 [1] => true,
-                _ => return Err(()),
+                _ => return Err("invalid pre version"),
             };
 
             let version = ApiVersion {
@@ -206,27 +206,27 @@ impl BootloaderConfig {
                 physical_memory: match physical_memory_some {
                     [0] if physical_memory == [0; 9] => Option::None,
                     [1] => Option::Some(Mapping::deserialize(&physical_memory)?),
-                    _ => return Err(()),
+                    _ => return Err("invalid phys memory value"),
                 },
                 page_table_recursive: match page_table_recursive_some {
                     [0] if page_table_recursive == [0; 9] => Option::None,
                     [1] => Option::Some(Mapping::deserialize(&page_table_recursive)?),
-                    _ => return Err(()),
+                    _ => return Err("invalid page table recursive value"),
                 },
                 aslr: match alsr {
                     1 => true,
                     0 => false,
-                    _ => return Err(()),
+                    _ => return Err("invalid aslr value"),
                 },
                 dynamic_range_start: match dynamic_range_start_some {
                     [0] if dynamic_range_start == [0; 8] => Option::None,
                     [1] => Option::Some(u64::from_le_bytes(dynamic_range_start)),
-                    _ => return Err(()),
+                    _ => return Err("invalid dynamic range start value"),
                 },
                 dynamic_range_end: match dynamic_range_end_some {
                     [0] if dynamic_range_end == [0; 8] => Option::None,
                     [1] => Option::Some(u64::from_le_bytes(dynamic_range_end)),
-                    _ => return Err(()),
+                    _ => return Err("invalid dynamic range end value"),
                 },
             };
             (mappings, s)
@@ -242,19 +242,19 @@ impl BootloaderConfig {
                 minimum_framebuffer_height: match min_framebuffer_height_some {
                     [0] if min_framebuffer_height == [0; 8] => Option::None,
                     [1] => Option::Some(u64::from_le_bytes(min_framebuffer_height)),
-                    _ => return Err(()),
+                    _ => return Err("minimum_framebuffer_height invalid"),
                 },
                 minimum_framebuffer_width: match min_framebuffer_width_some {
                     [0] if min_framebuffer_width == [0; 8] => Option::None,
                     [1] => Option::Some(u64::from_le_bytes(min_framebuffer_width)),
-                    _ => return Err(()),
+                    _ => return Err("minimum_framebuffer_width invalid"),
                 },
             };
             (frame_buffer, s)
         };
 
         if !s.is_empty() {
-            return Err(());
+            return Err("unexpected rest");
         }
 
         Ok(Self {
@@ -509,17 +509,17 @@ impl Mapping {
         }
     }
 
-    fn deserialize(serialized: &[u8; 9]) -> Result<Self, ()> {
+    fn deserialize(serialized: &[u8; 9]) -> Result<Self, &'static str> {
         let (&variant, s) = split_array_ref(serialized);
         let (&addr, s) = split_array_ref(s);
         if !s.is_empty() {
-            return Err(());
+            return Err("invalid mapping format");
         }
 
         match variant {
             [0] if addr == [0; 8] => Ok(Mapping::Dynamic),
             [1] => Ok(Mapping::FixedAddress(u64::from_le_bytes(addr))),
-            _ => Err(()),
+            _ => Err("invalid mapping value"),
         }
     }
 }

doc/chainloading.md renamed to docs/chainloading.md

@@ -0,0 +1,85 @@
+# Template: Create a Disk Image
+
+The [`bootloader`](https://docs.rs/bootloader/0.11) crate provides simple functions to create bootable disk images from a kernel. The basic idea is to build your kernel first and then invoke a builder function that calls the disk image creation functions of the `bootloader` crate.
+
+A good way to implement this is to move your kernel into a `kernel` subdirectory. Then you can create 
+a new `os` crate at the top level that defines a [workspace](https://doc.rust-lang.org/cargo/reference/workspaces.html). The root package has build-dependencies on the `kernel` [artifact](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies) and on the bootloader crate. This allows you to create the bootable disk image in a [cargo build script](https://doc.rust-lang.org/cargo/reference/build-scripts.html) and launch the created image in QEMU in the `main` function.
+
+The files could look like this:
+
+```toml
+# .cargo/config.toml
+
+[unstable]
+# enable the unstable artifact-dependencies feature, see
+# https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies
+bindeps = true
+```
+
+```toml
+# Cargo.toml
+
+[package]
+name = "os"         # or any other name
+version = "0.1.0"
+
+[build-dependencies]
+bootloader = "0.11"
+test-kernel = { path = "kernel", artifact = "bin", target = "x86_64-unknown-none" }
+
+[dependencies]
+# used for UEFI booting in QEMU
+ovmf_prebuilt = "0.1.0-alpha.1"
+
+[workspace]
+members = ["kernel"]
+```
+
+```rust
+// build.rs
+
+fn main() {
+    // set by cargo, build scripts should use this directory for output files
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    // set by cargo's artifact dependency feature, see
+    // https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#artifact-dependencies
+    let kernel = env!("CARGO_BIN_FILE_KERNEL_kernel");
+
+    // create an UEFI disk image (optional)
+    let uefi_path = out_dir.join("uefi.img");
+    bootloader::UefiBoot::new(&kernel).create_disk_image(uefi_path).unwrap();
+
+    // create a BIOS disk image (optional)
+    let out_bios_path = out_dir.join("bios.img");
+    bootloader::BiosBoot::new(&kernel).create_disk_image(uefi_path).unwrap();
+
+    // pass the disk image paths as env variables to the `main.rs`
+    println!("cargo:rustc-env=UEFI_PATH={}", uefi_path.display());
+    println!("cargo:rustc-env=BIOS_PATH={}", bios_path.display());
+}
+```
+
+```rust
+// src/main.rs
+
+fn main() {
+    // read env variables that were set in build script
+    let uefi_path = env!("UEFI_PATH");
+    let bios_path = env!("BIOS_PATH");
+    
+    // choose whether to start the UEFI or BIOS image
+    let uefi = true;
+
+    let mut cmd = std::process::Command::new("qemu-system-x86_64");
+    if uefi {
+        cmd.arg("-bios").arg(ovmf_prebuilt::ovmf_pure_efi());
+        cmd.arg("-drive").arg(format!("format=raw,file={uefi_path}"));
+    } else {
+        cmd.arg("-drive").arg(format!("format=raw,file={bios_path}"));
+    }
+    let mut child = cmd.spawn()?;
+    child.wait()?;
+}
+```
+
+Now you should be able to use `cargo build` to create a bootable disk image and `cargo run` to run in QEMU. Your kernel is automatically recompiled when it changes. For more advanced usage, you can add command-line arguments to your `main.rs` to e.g. pass additional arguments to QEMU or to copy the disk images to some path to make it easier to find them (e.g. for copying them to an thumb drive).

docs/create-disk-image.md

@@ -0,0 +1,41 @@
+# Migration from bootloader `v0.10`
+
+This guide summarizes the steps for migrating from `bootloader v0.10.X` to `bootloader v0.11`.
+
+## Kernel
+
+- Replace the `bootloader` dependency of your kernel with a dependency on the `bootloader_api` crate and adjust the import path in your `main.rs`:
+  ```diff
+   # in Cargo.toml
+
+  -bootloader = { version = "0.10.13" }
+  +bootloader_api = "0.11"
+  ```
+  ```diff
+   // in main.rs
+
+  -use bootloader::{entry_point, BootInfo};
+  +use bootloader_api::{entry_point, BootInfo};
+  ```
+- If you used optional features, such as `map-physical-memory`, you can enable them again through the `entry_point` macro:
+  ```rust
+  use bootloader_api::config::{BootloaderConfig, Mapping};
+
+  pub static BOOTLOADER_CONFIG: BootloaderConfig = {
+      let mut config = BootloaderConfig::new_default();
+      config.mappings.physical_memory = Some(Mapping::Dynamic);
+      config
+  };
+
+  // add a `config` argument to the `entry_point` macro call
+  entry_point!(kernel_main, config = &BOOTLOADER_CONFIG);
+  ```
+  See the [`BootloaderConfig`](https://docs.rs/bootloader_api/0.11/bootloader_api/config/struct.BootloaderConfig.html) struct for all configuration options.
+
+To build your kernel, run **`cargo build --target x86_64-unknown-none`**. Since the `x86_64-unknown-none` target is a Tier-2 target, there is no need for `bootimage`, `cargo-xbuild`, or `xargo` anymore. Instead, you can run `rustup target add x86_64-unknown-none` to download precompiled versions of the `core` and `alloc` crates. There is no need for custom JSON-based target files anymore.
+
+## Booting
+
+The `bootloader v0.11` release simplifies the disk image creation. The [`bootloader`](https://docs.rs/bootloader/0.11) crate now provides simple functions to create bootable disk images from a kernel. The basic idea is to build your kernel first and then invoke a builder function that calls the disk image creation functions of the `bootloader` crate.
+
+See our [disk image creation template](../create-disk-image.md) for a detailed explanation of the new build process.

docs/migration/v0.10.md

@@ -0,0 +1,49 @@
+# Migration from bootloader `v0.9`
+
+This guide summarizes the steps for migrating from `bootloader v0.9.X` to `bootloader v0.11`. Note that some bigger changes are required to support UEFI booting (to support the framebuffer and APIC).
+
+## Kernel
+
+- Replace the `bootloader` dependency of your kernel with a dependency on the `bootloader_api` crate:
+  ```diff
+  -bootloader = { version = "0.9.23", features = [...]}
+  +bootloader_api = "0.11"
+  ```
+- In your `main.rs`, adjust the import path and change the signature of the entry point function:
+  ```diff
+  -use bootloader::{entry_point, BootInfo};
+  +use bootloader_api::{entry_point, BootInfo};
+  
+   entry_point!(kernel_main);
+
+  -fn kernel_main(boot_info: &'static BootInfo) -> ! {
+  +fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
+  ```
+- If you used optional features, such as `map_physical_memory`, you can enable them again through the `entry_point` macro:
+  ```rust
+  use bootloader_api::config::{BootloaderConfig, Mapping};
+
+  pub static BOOTLOADER_CONFIG: BootloaderConfig = {
+      let mut config = BootloaderConfig::new_default();
+      config.mappings.physical_memory = Some(Mapping::Dynamic);
+      config
+  };
+
+  // add a `config` argument to the `entry_point` macro call
+  entry_point!(kernel_main, config = &BOOTLOADER_CONFIG);
+  ```
+  See the [`BootloaderConfig`](https://docs.rs/bootloader_api/0.11/bootloader_api/config/struct.BootloaderConfig.html) struct for all configuration options.
+- The `v0.11` version of the bootloader sets up a pixel-based framebuffer instead of using the VGA text mode. This means that you have to rewrite your screen output code. See the [`common/logger.rs`](../../common/src/logger.rs) module for an example implementation based on the [`noto-sans-mono-bitmap`](https://docs.rs/noto-sans-mono-bitmap/latest/noto_sans_mono_bitmap/index.html) and [`log`](https://docs.rs/log/latest) crates.
+- If you want to use UEFI booting, you cannot use the [legacy PIC](https://wiki.osdev.org/8259_PIC) for interrupt handling. Instead, you have to set up the [`APIC`](https://wiki.osdev.org/APIC). Unfortunately, we don't have a guide for this yet, but the basic steps are:
+  - The `boot_info.rsdp_addr` field will tell you the physical address of the [`RSDP`](https://wiki.osdev.org/RSDP) structure, which is part of the [`ACPI`](https://en.wikipedia.org/wiki/ACPI) standard. Note that `ACPI` (_Advanced Configuration and Power Interface_) and `APIC` (_Advanced Programmable Interrupt Controller_) are completely different things that just have confusingly similar acronyms.
+  - Use the [`acpi`](https://docs.rs/acpi/4.1.1/acpi/index.html) crate and its [`AcpiTables::from_rsdp`](https://docs.rs/acpi/4.1.1/acpi/struct.AcpiTables.html#method.from_rsdp) function to load the ACPI tables. Then use the [`platform_info`](https://docs.rs/acpi/4.1.1/acpi/struct.AcpiTables.html#method.platform_info) method and read the [`interrupt_model`](https://docs.rs/acpi/4.1.1/acpi/platform/struct.PlatformInfo.html#structfield.interrupt_model) field of the returned `PlatformInfo`. This field gives you all the necessary information about the system's interrupt controller.
+  - Parse and set up the local and IO APIC. We're working on a [crate](https://github.com/rust-osdev/apic) for that, but it's still in a very early state. We would love contributions! Alternatively, there are some other crates on crates.io that might work too.
+- If you reload the GDT at some point, ensure that all segment registers are written, including `ss` and `ds`. The `v0.9` version of the bootloader used to initialize some of them to 0, but this is no longer the case. If you don't do this, [a general protection fault might happen on `iretq`](https://github.com/rust-osdev/bootloader/issues/196).
+
+To build your kernel, run **`cargo build --target x86_64-unknown-none`**. Since the `x86_64-unknown-none` target is a Tier-2 target, there is no need for `bootimage`, `cargo-xbuild`, or `xargo` anymore. Instead, you can run `rustup target add x86_64-unknown-none` to download precompiled versions of the `core` and `alloc` crates. There is no need for custom JSON-based target files anymore.
+
+## Booting
+
+The `bootloader v0.11` release does not use the `bootimage` tool anymore. Instead, the [`bootloader`](https://docs.rs/bootloader/0.11) crate provides functions to create bootable disk images from a kernel. The basic idea is to build your kernel first and then invoke a builder function that calls the disk image creation functions of the `bootloader` crate.
+
+See our [disk image creation template](../create-disk-image.md) for a detailed explanation of the new build process.