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Philipp Oppermann
2019-09-29 15:24:21 +02:00
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blog/content/first-edition/posts/01-multiboot-kernel/index.md
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@@ -187,7 +187,7 @@ Idx Name Size VMA LMA File off Algn
```
_Note_: The `ld` and `objdump` commands are platform specific. If you're _not_ working on x86_64 architecture, you will need to [cross compile binutils]. Then use `x86_64‑elf‑ld` and `x86_64‑elf‑objdump` instead of `ld` and `objdump`.
[cross compile binutils]: ./first-edition/extra/cross-compile-binutils.md
[cross compile binutils]: @/first-edition/extra/cross-compile-binutils.md
## Creating the ISO
All PC BIOSes know how to boot from a CD-ROM, so we want to create a bootable CD-ROM image, containing our kernel and the GRUB bootloader's files, in a single file called an [ISO](https://en.wikipedia.org/wiki/ISO_image). Make the following directory structure and copy the `kernel.bin` to the right place:
@@ -315,7 +315,7 @@ Now we can invoke `make` and all updated assembly files are compiled and linked.
In the [next post] we will create a page table and do some CPU configuration to switch to the 64-bit [long mode].
[next post]: ./first-edition/posts/02-entering-longmode/index.md
[next post]: @/first-edition/posts/02-entering-longmode/index.md
[long mode]: https://en.wikipedia.org/wiki/Long_mode
## Footnotes

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@@ -11,7 +11,7 @@ updated = "2015-10-29"
In the [previous post] we created a minimal multiboot kernel. It just prints `OK` and hangs. The goal is to extend it and call 64-bit [Rust] code. But the CPU is currently in [protected mode] and allows only 32-bit instructions and up to 4GiB memory. So we need to set up _Paging_ and switch to the 64-bit [long mode] first.
[previous post]: ./first-edition/posts/01-multiboot-kernel/index.md
[previous post]: @/first-edition/posts/01-multiboot-kernel/index.md
[Rust]: http://www.rust-lang.org/
[protected mode]: https://en.wikipedia.org/wiki/Protected_mode
[long mode]: https://en.wikipedia.org/wiki/Long_mode
@@ -39,7 +39,7 @@ error:
At address `0xb8000` begins the so-called [VGA text buffer]. It's an array of screen characters that are displayed by the graphics card. A [future post] will cover the VGA buffer in detail and create a Rust interface to it. But for now, manual bit-fiddling is the easiest option.
[VGA text buffer]: https://en.wikipedia.org/wiki/VGA-compatible_text_mode
[future post]: ./first-edition/posts/04-printing-to-screen/index.md
[future post]: @/first-edition/posts/04-printing-to-screen/index.md
A screen character consists of a 8 bit color code and a 8 bit [ASCII] character. We used the color code `4f` for all characters, which means white text on red background. `0x52` is an ASCII `R`, `0x45` is an `E`, `0x3a` is a `:`, and `0x20` is a space. The second space is overwritten by the given ASCII byte. Finally the CPU is stopped with the `hlt` instruction.
@@ -492,8 +492,8 @@ _Congratulations_! You have successfully wrestled through this CPU configuration
#### One Last Thing
Above, we reloaded the code segment register `cs` with the new GDT offset. However, the data segment registers `ss`, `ds`, `es`, `fs`, and `gs` still contain the data segment offsets of the old GDT. This isn't necessarily bad, since they're ignored by almost all instructions in 64-bit mode. However, there are a few instructions that expect a valid data segment descriptor _or the null descriptor_ in those registers. An example is the the [iretq] instruction that we'll need in the [_Returning from Exceptions_] post.
[iretq]: ./first-edition/extra/naked-exceptions/03-returning-from-exceptions/index.md#the
[_Returning from Exceptions_]: ./first-edition/extra/naked-exceptions/03-returning-from-exceptions/index.md
[iretq]: @/first-edition/extra/naked-exceptions/03-returning-from-exceptions/index.md#the
[_Returning from Exceptions_]: @/first-edition/extra/naked-exceptions/03-returning-from-exceptions/index.md
To avoid future problems, we reload all data segment registers with null:
@@ -515,7 +515,7 @@ long_mode_start:
It's time to finally leave assembly behind and switch to [Rust]. Rust is a systems language without garbage collections that guarantees memory safety. Through a real type system and many abstractions it feels like a high-level language but can still be low-level enough for OS development. The [next post] describes the Rust setup.
[Rust]: https://www.rust-lang.org/
[next post]: ./first-edition/posts/03-set-up-rust/index.md
[next post]: @/first-edition/posts/03-set-up-rust/index.md
## Footnotes
[^hardware_lookup]: In the x86 architecture, the page tables are _hardware walked_, so the CPU will look at the table on its own when it needs a translation. Other architectures, for example MIPS, just throw an exception and let the OS translate the virtual address.

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@@ -11,8 +11,8 @@ updated = "2017-04-12"
In the previous posts we created a [minimal Multiboot kernel][multiboot post] and [switched to Long Mode][long mode post]. Now we can finally switch to [Rust] code. Rust is a high-level language without runtime. It allows us to not link the standard library and write bare metal code. Unfortunately the setup is not quite hassle-free yet.
[multiboot post]: ./first-edition/posts/01-multiboot-kernel/index.md
[long mode post]: ./first-edition/posts/02-entering-longmode/index.md
[multiboot post]: @/first-edition/posts/01-multiboot-kernel/index.md
[long mode post]: @/first-edition/posts/02-entering-longmode/index.md
[Rust]: https://www.rust-lang.org/
<!-- more -->
@@ -92,7 +92,7 @@ Let's define some properties of our target system:
- **No SSE**: Our target might not have [SSE] support. Even if it does, we probably don't want to use SSE instructions in our kernel, because it makes interrupt handling much slower. We will explain this in detail in the [“Handling Exceptions”] post.
- **No hardware floats**: The `x86_64` architecture uses SSE instructions for floating point operations, which we don't want to use (see the previous point). So we also need to avoid hardware floating point operations in our kernel. Instead, we will use _soft floats_, which are basically software functions that emulate floating point operations using normal integers.
[“Handling Exceptions”]: ./first-edition/posts/09-handling-exceptions/index.md
[“Handling Exceptions”]: @/first-edition/posts/09-handling-exceptions/index.md
### Target Specifications
Rust allows us to define [custom targets] through a JSON configuration file. A minimal target specification equal to `x86_64-unknown-linux-gnu` (the default 64-bit Linux target) looks like this:
@@ -486,10 +486,10 @@ Some notes:
### Stack Overflows
Since we still use the small 64 byte [stack from the last post], we must be careful not to [overflow] it. Normally, Rust tries to avoid stack overflows through _guard pages_: The page below the stack isn't mapped and such a stack overflow triggers a page fault (instead of silently overwriting random memory). But we can't unmap the page below our stack right now since we currently use only a single big page. Fortunately the stack is located just above the page tables. So some important page table entry would probably get overwritten on stack overflow and then a page fault occurs, too.
[stack from the last post]: ./first-edition/posts/02-entering-longmode/index.md#creating-a-stack
[stack from the last post]: @/first-edition/posts/02-entering-longmode/index.md#creating-a-stack
[overflow]: https://en.wikipedia.org/wiki/Stack_overflow
## What's next?
Until now we write magic bits to some memory location when we want to print something to screen. In the [next post] we create a abstraction for the VGA text buffer that allows us to print strings in different colors and provides a simple interface.
[next post]: ./first-edition/posts/04-printing-to-screen/index.md
[next post]: @/first-edition/posts/04-printing-to-screen/index.md

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@@ -11,7 +11,7 @@ updated = "2016-10-31"
In the [previous post] we switched from assembly to [Rust], a systems programming language that provides great safety. But so far we are using unsafe features like [raw pointers] whenever we want to print to screen. In this post we will create a Rust module that provides a safe and easy-to-use interface for the VGA text buffer. It will support Rust's [formatting macros], too.
[previous post]: ./first-edition/posts/03-set-up-rust/index.md
[previous post]: @/first-edition/posts/03-set-up-rust/index.md
[Rust]: https://www.rust-lang.org/
[raw pointers]: https://doc.rust-lang.org/book/raw-pointers.html
[formatting macros]: https://doc.rust-lang.org/std/fmt/#related-macros
@@ -642,7 +642,7 @@ In the next posts we will map the kernel pages correctly so that accessing `0x0`
The [next post] describes the Multiboot information structure and creates a frame allocator using the information about memory areas.
[next post]: ./first-edition/posts/05-allocating-frames/index.md
[next post]: @/first-edition/posts/05-allocating-frames/index.md
## Other Rust OS Projects
Now that you know the very basics of OS development in Rust, you should also check out the following projects:
@@ -658,7 +658,7 @@ _Note_: You need to [cross compile binutils] to build it (or you create some sym
[Rust Bare-Bones Kernel]: https://github.com/thepowersgang/rust-barebones-kernel
[higher half]: http://wiki.osdev.org/Higher_Half_Kernel
[cross compile binutils]: ./first-edition/extra/cross-compile-binutils.md
[cross compile binutils]: @/first-edition/extra/cross-compile-binutils.md
[RustOS]: https://github.com/RustOS-Fork-Holding-Ground/RustOS
["Tifflin" Experimental Kernel]:https://github.com/thepowersgang/rust_os
[Redox]: https://github.com/redox-os/redox

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@@ -430,10 +430,10 @@ Now we have a working frame allocator. It is a bit rudimentary and cannot free f
## What's next?
The [next post] will be about paging again. We will use the frame allocator to create a safe module that allows us to switch page tables and map pages. Then we will use this module and the information from the Elf-sections tag to remap the kernel correctly.
[next post]: ./first-edition/posts/06-page-tables/index.md
[next post]: @/first-edition/posts/06-page-tables/index.md
## Recommended Posts
Eric Kidd started the [Bare Metal Rust] series last week. Like this post, it builds upon the code from [Printing to Screen], but tries to support keyboard input instead of wrestling through memory management details.
[Bare Metal Rust]: http://www.randomhacks.net/bare-metal-rust/
[Printing to Screen]: ./first-edition/posts/04-printing-to-screen/index.md
[Printing to Screen]: @/first-edition/posts/04-printing-to-screen/index.md

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@@ -52,7 +52,7 @@ pub struct Page {
```
We import the `PAGE_SIZE` and define a constant for the number of entries per table. To make future function signatures more expressive, we can use the type aliases `PhysicalAddress` and `VirtualAddress`. The `Page` struct is similar to the `Frame` struct in the [previous post], but represents a virtual page instead of a physical frame.
[previous post]: ./first-edition/posts/05-allocating-frames/index.md#a-memory-module
[previous post]: @/first-edition/posts/05-allocating-frames/index.md#a-memory-module
### Page Table Entries
To model page table entries, we create a new `entry` submodule:
@@ -652,7 +652,7 @@ pub struct ActivePageTable {
```
We can't store the `Table<Level4>` directly because it needs to be at a special memory location (like the [VGA text buffer]). We could use a raw pointer or `&mut` instead of [Unique], but Unique indicates ownership better.
[VGA text buffer]: ./first-edition/posts/04-printing-to-screen/index.md#the-text-buffer
[VGA text buffer]: @/first-edition/posts/04-printing-to-screen/index.md#the-text-buffer
[Unique]: https://doc.rust-lang.org/1.10.0/core/ptr/struct.Unique.html
Because the `ActivePageTable` owns the unique recursive mapped P4 table, there must be only one `ActivePageTable` instance. Thus we make the constructor function unsafe:
@@ -881,7 +881,7 @@ This post has become pretty long. So let's summarize what we've done:
## What's next?
In the [next post] we will extend this module and add a function to modify inactive page tables. Through that function, we will create a new page table hierarchy that maps the kernel correctly using 4KiB pages. Then we will switch to the new table to get a safer kernel environment.
[next post]: ./first-edition/posts/07-remap-the-kernel/index.md
[next post]: @/first-edition/posts/07-remap-the-kernel/index.md
Afterwards, we will use this paging module to build a heap allocator. This will allow us to use allocation and collection types such as `Box` and `Vec`.

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@@ -21,18 +21,18 @@ As always, you can find the source code on [GitHub]. Don't hesitate to file issu
In the [previous post], we had a strange bug in the `unmap` function. Its reason was a silent stack overflow, which corrupted the page tables. Fortunately, our kernel stack is right above the page tables so that we noticed the overflow relatively quickly. This won't be the case when we add threads with new stacks in the future. Then a silent stack overflow could overwrite some data without us noticing. But eventually some completely unrelated function fails because a variable changed its value.
[previous post]: ./first-edition/posts/06-page-tables/index.md
[previous post]: @/first-edition/posts/06-page-tables/index.md
As you can imagine, these kinds of bugs are horrendous to debug. For that reason we will create a new hierarchical page table in this post, which has _guard page_ below the stack. A guard page is basically an unmapped page that causes a page fault when accessed. Thus we can catch stack overflows right when they happen.
Also, we will use the [information about kernel sections] to map the various sections individually instead of blindly mapping the first gigabyte. To improve safety even further, we will set the correct page table flags for the various sections. Thus it won't be possible to modify the contents of `.text` or to execute code from `.data` anymore.
[information about kernel sections]: ./first-edition/posts/05-allocating-frames/index.md#kernel-elf-sections
[information about kernel sections]: @/first-edition/posts/05-allocating-frames/index.md#kernel-elf-sections
## Preparation
There are many things that can go wrong when we switch to a new table. Therefore it's a good idea to [set up a debugger][set up gdb]. You should not need it when you follow this post, but it's good to know how to debug a problem when it occurs[^fn-debug-notes].
[set up gdb]: ./first-edition/extra/set-up-gdb/index.md
[set up gdb]: @/first-edition/extra/set-up-gdb/index.md
We also update the `Page` and `Frame` types to make our lives easier. The `Page` struct gets some derived traits:
@@ -281,7 +281,7 @@ pub fn map_table_frame(&mut self,
```
This function interprets the given frame as a page table frame and returns a `Table` reference. We return a table of level 1 because it [forbids calling the `next_table` methods][some clever solution]. Calling `next_table` must not be possible since it's not a page of the recursive mapping. To be able to return a `Table<Level1>`, we need to make the `Level1` enum in `memory/paging/table.rs` public.
[some clever solution]: ./first-edition/posts/06-page-tables/index.md#some-clever-solution
[some clever solution]: @/first-edition/posts/06-page-tables/index.md#some-clever-solution
The `unsafe` block is safe since the `VirtualAddress` returned by the `map` function is always valid and the type cast just reinterprets the frame's content.
@@ -554,7 +554,7 @@ First, we create a temporary page at page number `0xcafebabe`. We could use `0xd
Then we use the `with` function to temporary change the recursive mapping and execute the closure as if the `new_table` were active. This allows us to map the sections in the new table without changing the active mapping. To get the kernel sections, we use the [Multiboot information structure].
[Multiboot information structure]: ./first-edition/posts/05-allocating-frames/index.md#the-multiboot-information-structure
[Multiboot information structure]: @/first-edition/posts/05-allocating-frames/index.md#the-multiboot-information-structure
Let's resolve the above `TODO` by identity mapping the sections:
@@ -806,7 +806,7 @@ Let's cross our fingers and run it…
### Debugging
A QEMU boot loop indicates that some CPU exception occurred. We can see all thrown CPU exception by starting QEMU with `-d int` (as described [here][qemu debugging]):
[qemu debugging]: ./first-edition/posts/03-set-up-rust/index.md#debugging
[qemu debugging]: @/first-edition/posts/03-set-up-rust/index.md#debugging
```bash
> qemu-system-x86_64 -d int -no-reboot -cdrom build/os-x86_64.iso
@@ -831,8 +831,8 @@ These lines are the important ones. We can read many useful information from the
[osdev exception overview]: http://wiki.osdev.org/Exceptions
[page fault]: http://wiki.osdev.org/Exceptions#Page_Fault
[page fault error code]: http://wiki.osdev.org/Exceptions#Error_code
[GDT segment]: ./first-edition/posts/02-entering-longmode/index.md#loading-the-gdt
[VGA text buffer]: ./first-edition/posts/04-printing-to-screen/index.md#the-vga-text-buffer
[GDT segment]: @/first-edition/posts/02-entering-longmode/index.md#loading-the-gdt
[VGA text buffer]: @/first-edition/posts/04-printing-to-screen/index.md#the-vga-text-buffer
So let's find out which function caused the exception:
@@ -1030,7 +1030,7 @@ The final step is to create a guard page for our kernel stack.
The decision to place the kernel stack right above the page tables was already useful to detect a silent stack overflow in the [previous post][silent stack overflow]. Now we profit from it again. Let's look at our assembly `.bss` section again to understand why:
[silent stack overflow]: ./first-edition/posts/06-page-tables/index.md#translate
[silent stack overflow]: @/first-edition/posts/06-page-tables/index.md#translate
```nasm
; in src/arch/x86_64/boot.asm
@@ -1091,7 +1091,7 @@ Unfortunately stack probes require compiler support. They already work on Window
## What's next?
Now that we have a (mostly) safe kernel stack and a working page table module, we can add a virtual memory allocator. The [next post] will explore Rust's allocator API and create a very basic allocator. At the end of that post, we will be able to use Rust's allocation and collections types such as [Box], [Vec], or even [BTreeMap].
[next post]: ./first-edition/posts/08-kernel-heap/index.md
[next post]: @/first-edition/posts/08-kernel-heap/index.md
[Box]: https://doc.rust-lang.org/nightly/alloc/boxed/struct.Box.html
[Vec]: https://doc.rust-lang.org/1.10.0/collections/vec/struct.Vec.html
[BTreeMap]: https://doc.rust-lang.org/1.10.0/collections/btree_map/struct.BTreeMap.html

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@@ -10,8 +10,8 @@ template = "first-edition/page.html"
In the previous posts we created a [frame allocator] and a [page table module]. Now we are ready to create a kernel heap and a memory allocator. Thus, we will unlock `Box`, `Vec`, `BTreeMap`, and the rest of the [alloc] crate.
[frame allocator]: ./first-edition/posts/05-allocating-frames/index.md
[page table module]: ./first-edition/posts/06-page-tables/index.md
[frame allocator]: @/first-edition/posts/05-allocating-frames/index.md
[page table module]: @/first-edition/posts/06-page-tables/index.md
[alloc]: https://doc.rust-lang.org/nightly/alloc/index.html
<!-- more -->
@@ -460,8 +460,8 @@ That's it. Now our `memory::init` function can only be called once. The macro wo
### Mapping the Heap
Now we're ready to map the heap pages. In order to do it, we need access to the `ActivePageTable` or `Mapper` instance (see the [page table] and [kernel remapping] posts). For that we return it from the `paging::remap_the_kernel` function:
[page table]: ./first-edition/posts/06-page-tables/index.md
[kernel remapping]: ./first-edition/posts/07-remap-the-kernel/index.md
[page table]: @/first-edition/posts/06-page-tables/index.md
[kernel remapping]: @/first-edition/posts/07-remap-the-kernel/index.md
```rust
// in src/memory/paging/mod.rs
@@ -736,4 +736,4 @@ Now we're able to use heap storage in our kernel without leaking memory. This al
## What's next?
This post concludes the section about memory management for now. We will revisit this topic eventually, but now it's time to explore other topics. The upcoming posts will be about CPU exceptions and interrupts. We will catch all page, double, and triple faults and create a driver to read keyboard input. The [next post] starts by setting up a so-called _Interrupt Descriptor Table_.
[next post]: ./first-edition/posts/09-handling-exceptions/index.md
[next post]: @/first-edition/posts/09-handling-exceptions/index.md

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@@ -229,7 +229,7 @@ The breakpoint exception is commonly used in debuggers: When the user sets a bre
For our use case, we don't need to overwrite any instructions (it wouldn't even be possible since we [set the page table flags] to read-only). Instead, we just want to print a message when the breakpoint instruction is executed and then continue the program.
[set the page table flags]: ./first-edition/posts/07-remap-the-kernel/index.md#using-the-correct-flags
[set the page table flags]: @/first-edition/posts/07-remap-the-kernel/index.md#using-the-correct-flags
So let's create a simple `breakpoint_handler` function and add it to our IDT:
@@ -461,7 +461,7 @@ The documentation of the [`Idt`] struct and the [OSDev Wiki][osdev wiki exceptio
## Too much Magic?
The `x86-interrupt` calling convention and the [`Idt`] type made the exception handling process relatively straightforward and painless. If this was too much magic for you and you like to learn all the gory details of exception handling, we got you covered: Our [“Handling Exceptions with Naked Functions”] series shows how to handle exceptions without the `x86-interrupt` calling convention and also creates its own `Idt` type. Historically, these posts were the main exception handling posts before the `x86-interrupt` calling convention and the `x86_64` crate existed.
[“Handling Exceptions with Naked Functions”]: ./first-edition/extra/naked-exceptions/_index.md
[“Handling Exceptions with Naked Functions”]: @/first-edition/extra/naked-exceptions/_index.md
## What's next?
We've successfully caught our first exception and returned from it! The next step is to add handlers for other common exceptions such as page faults. We also need to make sure that we never cause a [triple fault], since it causes a complete system reset. The next post explains how we can avoid this by correctly catching [double faults].

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@@ -20,7 +20,7 @@ As always, the complete source code is available on [GitHub]. Please file [issue
## What is a Double Fault?
In simplified terms, a double fault is a special exception that occurs when the CPU fails to invoke an exception handler. For example, it occurs when a page fault is triggered but there is no page fault handler registered in the [Interrupt Descriptor Table][IDT] (IDT). So it's kind of similar to catch-all blocks in programming languages with exceptions, e.g. `catch(...)` in C++ or `catch(Exception e)` in Java or C#.
[IDT]: ./first-edition/posts/09-handling-exceptions/index.md#the-interrupt-descriptor-table
[IDT]: @/first-edition/posts/09-handling-exceptions/index.md#the-interrupt-descriptor-table
A double fault behaves like a normal exception. It has the vector number `8` and we can define a normal handler function for it in the IDT. It is really important to provide a double fault handler, because if a double fault is unhandled a fatal _triple fault_ occurs. Triple faults can't be caught and most hardware reacts with a system reset.
@@ -119,7 +119,7 @@ For example, what happens if… :
3. a divide-by-zero handler causes a breakpoint exception, but the breakpoint handler is swapped out?
4. our kernel overflows its stack and the [guard page] is hit?
[guard page]: ./first-edition/posts/07-remap-the-kernel/index.md#creating-a-guard-page
[guard page]: @/first-edition/posts/07-remap-the-kernel/index.md#creating-a-guard-page
Fortunately, the AMD64 manual ([PDF][AMD64 manual]) has an exact definition (in Section 8.2.9). According to it, a “double fault exception _can_ occur when a second exception occurs during the handling of a prior (first) exception handler”. The _“can”_ is important: Only very specific combinations of exceptions lead to a double fault. These combinations are:
@@ -199,7 +199,7 @@ struct InterruptStackTable {
For each exception handler, we can choose a stack from the IST through the `options` field in the corresponding [IDT entry]. For example, we could use the first stack in the IST for our double fault handler. Then the CPU would automatically switch to this stack whenever a double fault occurs. This switch would happen before anything is pushed, so it would prevent the triple fault.
[IDT entry]: ./first-edition/posts/09-handling-exceptions/index.md#the-interrupt-descriptor-table
[IDT entry]: @/first-edition/posts/09-handling-exceptions/index.md#the-interrupt-descriptor-table
### Allocating a new Stack
In order to fill an Interrupt Stack Table later, we need a way to allocate new stacks. Therefore we extend our `memory` module with a new `stack_allocator` submodule:
@@ -230,7 +230,7 @@ impl StackAllocator {
```
We create a simple `StackAllocator` that allocates stacks from a given range of pages (`PageIter` is an Iterator over a range of pages; we introduced it [in the kernel heap post].).
[in the kernel heap post]: ./first-edition/posts/08-kernel-heap/index.md#mapping-the-heap
[in the kernel heap post]: @/first-edition/posts/08-kernel-heap/index.md#mapping-the-heap
We add a `alloc_stack` method that allocates a new stack:
@@ -285,8 +285,8 @@ impl StackAllocator {
```
The method takes mutable references to the [ActivePageTable] and a [FrameAllocator], since it needs to map the new virtual stack pages to physical frames. We define that the stack size is a multiple of the page size.
[ActivePageTable]: ./first-edition/posts/06-page-tables/index.md#page-table-ownership
[FrameAllocator]: ./first-edition/posts/05-allocating-frames/index.md#a-frame-allocator
[ActivePageTable]: @/first-edition/posts/06-page-tables/index.md#page-table-ownership
[FrameAllocator]: @/first-edition/posts/05-allocating-frames/index.md#a-frame-allocator
Instead of operating directly on `self.range`, we [clone] it and only write it back on success. This way, subsequent stack allocations can still succeed if there are pages left (e.g., a call with `size_in_pages = 3` can still succeed after a failed call with `size_in_pages = 100`).
@@ -297,7 +297,7 @@ In order to be able to clone `PageIter`, we add a `#[derive(Clone)]` to its defi
The actual allocation is straightforward: First, we choose the next page as [guard page]. Then we choose the next `size_in_pages` pages as stack pages using [Iterator::nth]. If all three variables are `Some`, the allocation succeeded and we map the stack pages to physical frames using [ActivePageTable::map]. The guard page remains unmapped.
[Iterator::nth]: https://doc.rust-lang.org/nightly/core/iter/trait.Iterator.html#method.nth
[ActivePageTable::map]: ./first-edition/posts/06-page-tables/index.md#more-mapping-functions
[ActivePageTable::map]: @/first-edition/posts/06-page-tables/index.md#more-mapping-functions
Finally, we create and return a new `Stack`, which we define as follows:
@@ -505,7 +505,7 @@ The Global Descriptor Table (GDT) is a relict that was used for [memory segmenta
We already created a GDT [when switching to long mode]. Back then, we used assembly to create valid code and data segment descriptors, which were required to enter 64-bit mode. We could just edit that assembly file and add an additional TSS descriptor. However, we now have the expressiveness of Rust, so let's do it in Rust instead.
[when switching to long mode]: ./first-edition/posts/02-entering-longmode/index.md#the-global-descriptor-table
[when switching to long mode]: @/first-edition/posts/02-entering-longmode/index.md#the-global-descriptor-table
We start by creating a new `interrupts::gdt` submodule. For that we need to rename the `src/interrupts.rs` file to `src/interrupts/mod.rs`. Then we can create a new submodule: