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Merge pull request #575 from phil-opp/update-bootloader-bootimage
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Update to new bootloader 0.5.1 and bootimage 0.7.2
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phil-opp authored Apr 6, 2019
2 parents beb1306 + 6015feb commit 4c01a96
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Expand Up @@ -343,7 +343,7 @@ Instead of writing our own bootloader, which is a project on its own, we use the
# in Cargo.toml

[dependencies]
bootloader = "0.4.0"
bootloader = "0.5.1"
```

Adding the bootloader as dependency is not enough to actually create a bootable disk image. The problem is that we need to combine the bootloader with the kernel after it has been compiled, but cargo has no support for additional build steps after successful compilation (see [this issue][post-build script] for more information).
Expand All @@ -353,20 +353,22 @@ Adding the bootloader as dependency is not enough to actually create a bootable
To solve this problem, we created a tool named `bootimage` that first compiles the kernel and bootloader, and then combines them to create a bootable disk image. To install the tool, execute the following command in your terminal:

```
cargo install bootimage --version "^0.5.0"
cargo install bootimage --version "^0.7.1"
```

The `^0.5.0` is a so-called [_caret requirement_], which means "version `0.5.0` or a later compatible version". So if we find a bug and publish version `0.5.1` or `0.5.2`, cargo would automatically use the latest version, as long as it is still a version `0.5.x`. However, it wouldn't choose version `0.6.0`, because it is not considered as compatible. Note that dependencies in your `Cargo.toml` are caret requirements by default, so the same rules are applied to our bootloader dependency.
The `^0.7.1` is a so-called [_caret requirement_], which means "version `0.7.1` or a later compatible version". So if we find a bug and publish version `0.7.2` or `0.7.3`, cargo would automatically use the latest version, as long as it is still a version `0.7.x`. However, it wouldn't choose version `0.8.0`, because it is not considered as compatible. Note that dependencies in your `Cargo.toml` are caret requirements by default, so the same rules are applied to our bootloader dependency.

[_caret requirement_]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#caret-requirements

After installing the `bootimage` tool, creating a bootable disk image is as easy as executing:
For running `bootimage` and building the bootloader, you need to have the `llvm-tools-preview` rustup component installed. You can do so by executing `rustup component add llvm-tools-preview`.

After installing `bootimage` and adding the `llvm-tools-preview` component, we can create a bootable disk image by executing:

```
> bootimage build --target x86_64-blog_os.json
```

You see that the tool recompiles your kernel using `cargo xbuild`, so it will automatically pick up any changes you make. Afterwards it compiles the bootloader, which might take a while. Like all crate dependencies it is only built once and then cached, so subsequent builds will be much faster. Finally, `bootimage` combines the bootloader and your kernel to a bootable disk image.
We see that the tool recompiles our kernel using `cargo xbuild`, so it will automatically pick up any changes you make. Afterwards it compiles the bootloader, which might take a while. Like all crate dependencies it is only built once and then cached, so subsequent builds will be much faster. Finally, `bootimage` combines the bootloader and your kernel to a bootable disk image.

After executing the command, you should see a bootable disk image named `bootimage-blog_os.bin` in your `target/x86_64-blog_os/debug` directory. You can boot it in a virtual machine or copy it to an USB drive to boot it on real hardware. (Note that this is not a CD image, which have a different format, so burning it to a CD doesn't work).

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Expand Up @@ -47,11 +47,11 @@ To implement the approach, we will need support from the bootloader, so we'll co

### Dependency Updates

This post requires version 0.4.0 or later of the `bootloader` dependency and version 0.5.2 or later of the `x86_64` dependency. You can update the dependencies in your `Cargo.toml`:
This post requires version 0.5.1 or later of the `bootloader` dependency and version 0.5.2 or later of the `x86_64` dependency. You can update the dependencies in your `Cargo.toml`:

```toml
[dependencies]
bootloader = "0.4.0"
bootloader = "0.5.1"
x86_64 = "0.5.2"
```

Expand Down Expand Up @@ -305,7 +305,7 @@ We choose the first approach for our kernel since it is simple, platform-indepen

```toml
[dependencies]
bootloader = { version = "0.4.0", features = ["map_physical_memory"]}
bootloader = { version = "0.5.1", features = ["map_physical_memory"]}
```

With this feature enabled, the bootloader maps the complete physical memory to some unused virtual address range. To communicate the virtual address range to our kernel, the bootloader passes a _boot information_ structure.
Expand Down Expand Up @@ -342,7 +342,7 @@ Since our `_start` function is called externally from the bootloader, no checkin

To make sure that the entry point function has always the correct signature that the bootloader expects, the `bootloader` crate provides an [`entry_point`] macro that provides a type-checked way to define a Rust function as the entry point. Let's rewrite our entry point function to use this macro:

[`entry_point`]: https://docs.rs/bootloader/0.4.0/bootloader/macro.entry_point.html
[`entry_point`]: https://docs.rs/bootloader/0.5.1/bootloader/macro.entry_point.html

```rust
// in src/main.rs
Expand Down Expand Up @@ -889,7 +889,7 @@ This function uses iterator combinator methods to transform the initial `MemoryM
- The third step is the most complicated: We convert each range to an iterator through the `into_iter` method and then choose every 4096th address using [`step_by`]. Since 4096 bytes (= 4 KiB) is the page size, we get the start address of each frame. The bootloader page aligns all usable memory areas so that we don't need any alignment or rounding code here. By using [`flat_map`] instead of `map`, we get an `Iterator<Item = u64>` instead of an `Iterator<Item = Iterator<Item = u64>>`.
- In the final step, we convert the start addresses to `PhysFrame` types to construct the desired `Iterator<Item = PhysFrame>`. We then use this iterator to create and return a new `BootInfoFrameAllocator`.

[`MemoryRegion`]: https://docs.rs/bootloader/0.4.0/bootloader/bootinfo/struct.MemoryRegion.html
[`MemoryRegion`]: https://docs.rs/bootloader/0.5.1/bootloader/bootinfo/struct.MemoryRegion.html
[`filter`]: https://doc.rust-lang.org/core/iter/trait.Iterator.html#method.filter
[`map`]: https://doc.rust-lang.org/core/iter/trait.Iterator.html#method.map
[range syntax]: https://doc.rust-lang.org/core/ops/struct.Range.html
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