Parse bootloader configuration from kernel's Cargo.toml

Cargo.toml

@@ -26,10 +26,11 @@ optional = true
 
 [build-dependencies]
 llvm-tools = { version = "0.1", optional = true }
+toml = { version = "0.5.1", optional = true }
 
 [features]
 default = []
-binary = ["xmas-elf", "x86_64", "usize_conversions", "fixedvec", "llvm-tools"]
+binary = ["xmas-elf", "x86_64", "usize_conversions", "fixedvec", "llvm-tools", "toml"]
 vga_320x200 = ["font8x8"]
 recursive_page_table = []
 map_physical_memory = []

README.md

@@ -10,18 +10,43 @@ Written for the [second edition](https://github.com/phil-opp/blog_os/issues/360)
 
 TODO
 
+## Configuration
+
+The bootloader exposes a few variables which can be configured through the `Cargo.toml` of your kernel:
+
+```toml
+[package.metadata.bootloader]
+# The address at which the kernel stack is placed. If not provided, the bootloader
+# dynamically searches for a location.
+kernel-stack-address = "0xFFFFFF8000000000"
+
+# The size of the kernel stack, given in number of 4KiB pages. Defaults to 512.
+kernel-stack-size = 128
+
+# The virtual address offset from which physical memory is mapped, as described in
+# https://os.phil-opp.com/paging-implementation/#map-the-complete-physical-memory
+# Only applies if the `map_physical_memory` feature of the crate is enabled.
+# If not provided, the bootloader dynamically searches for a location.
+physical-memory-offset = "0xFFFF800000000000"
+```
+
+Note that the addresses **must** be given as strings (in either hex or decimal format), as [TOML](https://github.com/toml-lang/toml) does not support unsigned 64-bit integers.
+
 ## Requirements
 
 You need a nightly [Rust](https://www.rust-lang.org) compiler and [cargo xbuild](https://github.com/rust-osdev/cargo-xbuild). You also need the `llvm-tools-preview` component, which can be installed through `rustup component add llvm-tools-preview`.
 
 ## Build
 
-The simplest way to use the bootloader is in combination with the [bootimage](https://github.com/rust-osdev/bootimage) tool. This crate **requires at least bootimage 0.7.6**. With the tool installed, you can add a normal cargo dependency on the `bootloader` crate to your kernel and then run `bootimage build` to create a bootable disk image. You can also execute `bootimage run` to run your kernel in [QEMU](https://www.qemu.org/) (needs to be installed).
+The simplest way to use the bootloader is in combination with the [bootimage](https://github.com/rust-osdev/bootimage) tool. This crate **requires at least bootimage 0.7.7**. With the tool installed, you can add a normal cargo dependency on the `bootloader` crate to your kernel and then run `bootimage build` to create a bootable disk image. You can also execute `bootimage run` to run your kernel in [QEMU](https://www.qemu.org/) (needs to be installed).
 
-To compile the bootloader manually, you need to invoke `cargo xbuild` with a `KERNEL` environment variable that points to your kernel executable (in the ELF format):
+To compile the bootloader manually, you need to invoke `cargo xbuild` with two environment variables:
+* `KERNEL`: points to your kernel executable (in the ELF format)
+* `KERNEL_MANIFEST`: points to the `Cargo.toml` describing your kernel
 
+For example: 
 ```
-KERNEL=/path/to/your/kernel/target/debug/your_kernel cargo xbuild
+KERNEL=/path/to/your/kernel/target/debug/your_kernel KERNEL_MANIFEST=/path/to/your/kernel/Cargo.toml cargo xbuild
 ```
 
 As an example, you can build the bootloader with example kernel from the `example-kernel` directory with the following commands:
@@ -30,7 +55,7 @@ As an example, you can build the bootloader with example kernel from the `exampl
 cd example-kernel
 cargo xbuild
 cd ..
-KERNEL=example-kernel/target/x86_64-example-kernel/debug/example-kernel cargo xbuild --release --features binary
+KERNEL=example-kernel/target/x86_64-example-kernel/debug/example-kernel KERNEL_MANIFEST=example-kernel/Cargo.toml cargo xbuild --release --features binary
 ```
 
 The `binary` feature is required to enable the dependencies required for compiling the bootloader executable. The command results in a bootloader executable at `target/x86_64-bootloader.json/release/bootloader`. This executable is still an ELF file, which can't be run directly.
@@ -64,7 +89,7 @@ The bootloader crate can be configured through some cargo features:
 - `vga_320x200`: This feature switches the VGA hardware to mode 0x13, a graphics mode with resolution 320x200 and 256 colors per pixel. The framebuffer is linear and lives at address `0xa0000`.
 - `recursive_page_table`: Maps the level 4 page table recursively and adds the [`recursive_page_table_address`](https://docs.rs/bootloader/0.4.0/bootloader/bootinfo/struct.BootInfo.html#structfield.recursive_page_table_addr) field to the passed `BootInfo`.
 - `map_physical_memory`: Maps the complete physical memory in the virtual address space and passes a [`physical_memory_offset`](https://docs.rs/bootloader/0.4.0/bootloader/bootinfo/struct.BootInfo.html#structfield.physical_memory_offset) field in the `BootInfo`.
-  - The virtual address where the physical memory should be mapped is configurable by setting the `BOOTLOADER_PHYSICAL_MEMORY_OFFSET` environment variable (supports decimal and hex numbers (prefixed with `0x`)).
+  - The virtual address where the physical memory should be mapped is configurable by setting the `physical-memory-offset` field in the kernel's `Cargo.toml`, as explained in [Configuration](#Configuration).
 
 ## Advanced Documentation
 See these guides for advanced usage of this crate:

azure-pipelines.yml

@@ -96,7 +96,9 @@ steps:
 
 - script: cargo xbuild --bin bootloader --features binary --release
   displayName: 'Build Bootloader'
-  env: { KERNEL: "test-kernel/target/x86_64-test-kernel/debug/test-kernel" }
+  env:
+    KERNEL: "test-kernel/target/x86_64-test-kernel/debug/test-kernel"
+    KERNEL_MANIFEST: "test-kernel/Cargo.toml"
 
 - script: cargo objcopy -- -I elf64-x86-64 -O binary --binary-architecture=i386:x86-64 target/x86_64-bootloader/release/bootloader target/x86_64-bootloader/release/bootloader.bin
   displayName: 'Convert Bootloader ELF to Binary'

build.rs

@@ -11,34 +11,79 @@ fn main() {
 }
 
 #[cfg(feature = "binary")]
-fn num_from_env(env: &'static str, aligned: bool) -> Option<u64> {
-    use std::env;
-    match env::var(env) {
-        Err(env::VarError::NotPresent) => None,
-        Err(env::VarError::NotUnicode(_)) => {
-            panic!("The `{}` environment variable must be valid unicode", env,)
-        }
-        Ok(s) => {
-            let num = if s.starts_with("0x") {
-                u64::from_str_radix(&s[2..], 16)
-            } else {
-                u64::from_str_radix(&s, 10)
-            };
-
-            let num = num.expect(&format!(
-                "The `{}` environment variable must be an integer\
-                 (is `{}`).",
-                env, s
-            ));
+#[derive(Default)]
+struct BootloaderConfig {
+    physical_memory_offset: Option<u64>,
+    kernel_stack_address: Option<u64>,
+    kernel_stack_size: Option<u64>,
+}
+
+#[cfg(feature = "binary")]
+fn parse_aligned_addr(key: &str, value: &str) -> u64 {
+    let num = if value.starts_with("0x") {
+        u64::from_str_radix(&value[2..], 16)
+    } else {
+        u64::from_str_radix(&value, 10)
+    };
 
-            if aligned && num % 0x1000 != 0 {
+    let num = num.expect(&format!(
+        "`{}` in the kernel manifest must be an integer (is `{}`)",
+        key, value
+    ));
+
+    if num % 0x1000 != 0 {
+        panic!(
+            "`{}` in the kernel manifest must be aligned to 4KiB (is `{}`)",
+            key, value
+        );
+    } else {
+        num
+    }
+}
+
+#[cfg(feature = "binary")]
+fn parse_to_config(cfg: &mut BootloaderConfig, table: &toml::value::Table) {
+    use toml::Value;
+
+    for (key, value) in table {
+        match (key.as_str(), value.clone()) {
+            ("kernel-stack-address", Value::Integer(i))
+            | ("physical-memory-offset", Value::Integer(i)) => {
                 panic!(
-                    "The `{}` environment variable must be aligned to 0x1000 (is `{:#x}`).",
-                    env, num
+                    "`{0}` in the kernel manifest must be given as a string, \
+                     as toml does not support unsigned 64-bit integers (try `{0} = \"{1}\"`)",
+                    key.as_str(),
+                    i
+                );
+            }
+            ("kernel-stack-address", Value::String(s)) => {
+                cfg.kernel_stack_address = Some(parse_aligned_addr(key.as_str(), &s));
+            }
+            #[cfg(not(feature = "map_physical_memory"))]
+            ("physical-memory-offset", Value::String(_)) => {
+                panic!(
+                    "`physical-memory-offset` is only supported when the `map_physical_memory` \
+                     feature of the crate is enabled"
+                );
+            }
+            #[cfg(feature = "map_physical_memory")]
+            ("physical-memory-offset", Value::String(s)) => {
+                cfg.physical_memory_offset = Some(parse_aligned_addr(key.as_str(), &s));
+            }
+            ("kernel-stack-size", Value::Integer(i)) => {
+                if i <= 0 {
+                    panic!("`kernel-stack-size` in kernel manifest must be positive");
+                } else {
+                    cfg.kernel_stack_size = Some(i as u64);
+                }
+            }
+            (s, _) => {
+                panic!(
+                    "unknown key '{}' in kernel manifest \
+                     - you may need to update the bootloader crate",
+                    s
                 );
             }
-
-            Some(num)
         }
     }
 }
@@ -47,11 +92,12 @@ fn num_from_env(env: &'static str, aligned: bool) -> Option<u64> {
 fn main() {
     use std::{
         env,
-        fs::File,
+        fs::{self, File},
         io::Write,
         path::{Path, PathBuf},
         process::{self, Command},
     };
+    use toml::Value;
 
     let target = env::var("TARGET").expect("TARGET not set");
     if Path::new(&target)
@@ -185,22 +231,55 @@ fn main() {
         process::exit(1);
     }
 
+    // Parse the kernel's Cargo.toml which is given to us by bootimage
+    let mut bootloader_config = BootloaderConfig::default();
+
+    match env::var("KERNEL_MANIFEST") {
+        Err(env::VarError::NotPresent) => {
+            panic!("The KERNEL_MANIFEST environment variable must be set for building the bootloader.\n\n\
+                 If you use `bootimage` for building you need at least version 0.7.7. You can \
+                 update `bootimage` by running `cargo install bootimage --force`.");
+        }
+        Err(env::VarError::NotUnicode(_)) => {
+            panic!("The KERNEL_MANIFEST environment variable contains invalid unicode")
+        }
+        Ok(path) => {
+            println!("cargo:rerun-if-changed={}", path);
+
+            let contents = fs::read_to_string(&path).expect(&format!(
+                "failed to read kernel manifest file (path: {})",
+                path
+            ));
+
+            let manifest = contents
+                .parse::<Value>()
+                .expect("failed to parse kernel's Cargo.toml");
+
+            let table = manifest
+                .get("package")
+                .and_then(|table| table.get("metadata"))
+                .and_then(|table| table.get("bootloader"))
+                .and_then(|table| table.as_table());
+
+            if let Some(table) = table {
+                parse_to_config(&mut bootloader_config, table);
+            }
+        }
+    }
+
     // Configure constants for the bootloader
     // We leave some variables as Option<T> rather than hardcoding their defaults so that they
     // can be calculated dynamically by the bootloader.
     let file_path = out_dir.join("bootloader_config.rs");
     let mut file = File::create(file_path).expect("failed to create bootloader_config.rs");
-    let physical_memory_offset = num_from_env("BOOTLOADER_PHYSICAL_MEMORY_OFFSET", true);
-    let kernel_stack_address = num_from_env("BOOTLOADER_KERNEL_STACK_ADDRESS", true);
-    let kernel_stack_size = num_from_env("BOOTLOADER_KERNEL_STACK_SIZE", false);
     file.write_all(
         format!(
             "const PHYSICAL_MEMORY_OFFSET: Option<u64> = {:?};
             const KERNEL_STACK_ADDRESS: Option<u64> = {:?};
             const KERNEL_STACK_SIZE: u64 = {};",
-            physical_memory_offset,
-            kernel_stack_address,
-            kernel_stack_size.unwrap_or(512), // size is in number of pages
+            bootloader_config.physical_memory_offset,
+            bootloader_config.kernel_stack_address,
+            bootloader_config.kernel_stack_size.unwrap_or(512), // size is in number of pages
         )
         .as_bytes(),
     )
@@ -214,9 +293,7 @@ fn main() {
     );
 
     println!("cargo:rerun-if-env-changed=KERNEL");
-    println!("cargo:rerun-if-env-changed=BOOTLOADER_PHYSICAL_MEMORY_OFFSET");
-    println!("cargo:rerun-if-env-changed=BOOTLOADER_KERNEL_STACK_ADDRESS");
-    println!("cargo:rerun-if-env-changed=BOOTLOADER_KERNEL_STACK_SIZE");
+    println!("cargo:rerun-if-env-changed=KERNEL_MANIFEST");
     println!("cargo:rerun-if-changed={}", kernel.display());
     println!("cargo:rerun-if-changed=build.rs");
 }