Writing an OS in Rust (First Edition)

Philipp Oppermann's blog

Set Up Rust

No longer updated! You are viewing the a post of the first edition of “Writing an OS in Rust”, which is no longer updated. You can find the second edition here.

In the previous posts we created a minimal Multiboot kernel and switched to Long Mode. 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.

This blog post tries to set up Rust step-by-step and point out the different problems. If you have any questions, problems, or suggestions please file an issue or create a comment at the bottom. The code from this post is in a Github repository, too.

🔗Installing Rust

We need a nightly compiler, as we will use many unstable features. To manage Rust installations I highly recommend rustup. It allows you to install nightly, beta, and stable compilers side-by-side and makes it easy to update them. To use a nightly compiler for the current directory, you can run rustup override add nightly. Alternatively, you can add a file called rust-toolchain to the project’s root directory:


🔗Creating a Cargo project

Cargo is Rust’s excellent package manager. Normally you would call cargo new when you want to create a new project folder. We can’t use it because our folder already exists, so we need to do it manually. Fortunately we only need to add a cargo configuration file named Cargo.toml:

name = "blog_os"
version = "0.1.0"
authors = ["Philipp Oppermann <dev@phil-opp.com>"]

crate-type = ["staticlib"]

The package section contains required project metadata such as the semantic crate version. The lib section specifies that we want to build a static library, i.e. a library that contains all of its dependencies. This is required to link the Rust project with our kernel.

Now we place our root source file in src/lib.rs:


pub extern fn rust_main() {}

#[lang = "eh_personality"] #[no_mangle] pub extern fn eh_personality() {}
#[lang = "panic_fmt"] #[no_mangle] pub extern fn panic_fmt() -> ! {loop{}}

Let’s break it down:

🔗Building Rust

We can now build it using cargo build, which creates a static library at target/debug/libblog_os.a. However, the resulting library is specific to our host operating system. This is undesirable, because our target system might be different.

Let’s define some properties of our target system:

🔗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:

  "llvm-target": "x86_64-unknown-linux-gnu",
  "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
  "linker-flavor": "gcc",
  "target-endian": "little",
  "target-pointer-width": "64",
  "target-c-int-width": "32",
  "arch": "x86_64",
  "os": "linux"

The llvm-target field specifies the target triple that is passed to LLVM. Target triples are a naming convention that define the CPU architecture (e.g., x86_64 or arm), the vendor (e.g., apple or unknown), the operating system (e.g., windows or linux), and the ABI (e.g., gnu or msvc). For example, the target triple for 64-bit Linux is x86_64-unknown-linux-gnu and for 32-bit Windows the target triple is i686-pc-windows-msvc.

The data-layout field is also passed to LLVM and specifies how data should be laid out in memory. It consists of various specifications separated by a - character. For example, the e means little endian and S128 specifies that the stack should be 128 bits (= 16 byte) aligned. The format is described in detail in the LLVM documentation but there shouldn’t be a reason to change this string.

The linker-flavor field was recently introduced in #40018 with the intention to add support for the LLVM linker LLD, which is platform independent. In the future, this might allow easy cross compilation without the need to install a gcc cross compiler for linking.

The other fields are used for conditional compilation. This allows crate authors to use cfg variables to write special code for depending on the OS or the architecture. There isn’t any up-to-date documentation about these fields but the corresponding source code is quite readable.

🔗A Kernel Target Specification

For our target system, we define the following JSON configuration in a file named x86_64-blog_os.json:

  "llvm-target": "x86_64-unknown-none",
  "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
  "linker-flavor": "gcc",
  "target-endian": "little",
  "target-pointer-width": "64",
  "target-c-int-width": "32",
  "arch": "x86_64",
  "os": "none",
  "disable-redzone": true,
  "features": "-mmx,-sse,+soft-float"

As llvm-target we use x86_64-unknown-none, which defines the x86_64 architecture, an unknown vendor, and no operating system (none). The ABI doesn’t matter for us, so we just leave it off. The data-layout field is just copied from the x86_64-unknown-linux-gnu target. We also use the same values for the target-endian, target-pointer-width, target-c-int-width, and arch fields. For the os field we choose none, since our kernel runs on bare metal.

🔗The Red Zone

The red zone is an optimization of the System V ABI that allows functions to temporary use the 128 bytes below its stack frame without adjusting the stack pointer:

stack frame with red zone

The image shows the stack frame of a function with n local variables. On function entry, the stack pointer is adjusted to make room on the stack for the local variables.

The red zone is defined as the 128 bytes below the adjusted stack pointer. The function can use this area for temporary data that’s not needed across function calls. Thus, the two instructions for adjusting the stack pointer can be avoided in some cases (e.g. in small leaf functions).

However, this optimization leads to huge problems with exceptions or hardware interrupts. Let’s assume that an exception occurs while a function uses the red zone:

red zone overwritten by exception handler

The CPU and the exception handler overwrite the data in red zone. But this data is still needed by the interrupted function. So the function won’t work correctly anymore when we return from the exception handler. This might lead to strange bugs that take weeks to debug.

To avoid such bugs when we implement exception handling in the future, we disable the red zone right from the beginning. This is achieved by adding the "disable-redzone": true line to our target configuration file.

🔗SIMD Extensions

The features field enables/disables target features. We disable the mmx and sse features by prefixing them with a minus and enable the soft-float feature by prefixing it with a plus. The mmx and sse features determine support for Single Instruction Multiple Data (SIMD) instructions, which simultaneously perform an operation (e.g. addition) on multiple data words. The x86 architecture supports the following standards:

By using such SIMD standards, programs can often speed up significantly. Good compilers are able to transform normal loops into such SIMD code automatically through a process called auto-vectorization.

However, the large SIMD registers lead to problems in OS kernels. The reason is that the kernel has to backup all registers that it uses on each hardware interrupt (we will look into this in the “Handling Exceptions” post). So if the kernel uses SIMD registers, it has to backup a lot more data, which noticeably decreases performance. To avoid this performance loss, we disable the sse and mmx features (the avx feature is disabled by default).

As noted above, floating point operations on x86_64 use SSE registers, so floats are no longer usable without SSE. Unfortunately, the Rust core library already uses floats (e.g., it implements traits for f32 and f64), so we need an alternative way to implement float operations. The soft-float feature solves this problem by emulating all floating point operations through software functions based on normal integers.


To build our kernel for our new target, we pass the configuration file’s name as --target argument. There is currently an open bug for custom target specifications, so you also need to set the RUST_TARGET_PATH environment variable to the current directory, otherwise Rust doesn’t find your target. The full command is:

RUST_TARGET_PATH=$(pwd) cargo build --target x86_64-blog_os

However, the following error occurs:

error[E0463]: can't find crate for `core`
  = note: the `x86_64-blog_os` target may not be installed

The error tells us that the Rust compiler no longer finds the core library. The core library is implicitly linked to all no_std crates and contains things such as Result, Option, and iterators.

The problem is that the core library is distributed together with the Rust compiler as a precompiled library. So it is only valid for the host triple (e.g., x86_64-unknown-linux-gnu) but not for our custom target. If we want to compile code for other targets, we need to recompile core for these targets first.


That’s where xargo comes in. It is a wrapper for cargo that eases cross compilation. We can install it by executing:

cargo install xargo

Xargo depends on the rust source code, which we can install with rustup component add rust-src.

Xargo is “a drop-in replacement for cargo”, so every cargo command also works with xargo. You can do e.g. xargo --help, xargo clean, or xargo doc. However, the build command gains additional functionality: xargo build will automatically cross compile the core library when compiling for custom targets.

Let’s try it:

> RUST_TARGET_PATH=$(pwd) xargo build --target=x86_64-blog_os
   Compiling core v0.0.0 (file:///…/rust/src/libcore)
    Finished release [optimized] target(s) in 22.87 secs
   Compiling blog_os v0.1.0 (file:///…/blog_os/tags)
    Finished dev [unoptimized + debuginfo] target(s) in 0.29 secs

It worked! We see that xargo cross-compiled the core library for our new custom target and then continued to compile our blog_os crate. After compilation, we can find a static library at target/x86_64-blog_os/debug/libblog_os.a, which can be linked with our assembly kernel.

🔗Integrating Rust

Let’s try to integrate our Rust library into our assembly kernel so that we can call the rust_main function. For that we need to pass the libblog_os.a file to the linker, together with the assembly object files.

🔗Adjusting the Makefile

To build and link the rust library on make, we extend our Makefile(full file):

# ...
target ?= $(arch)-blog_os
rust_os := target/$(target)/debug/libblog_os.a
# ...
.PHONY: all clean run iso kernel
# ...
$(kernel): kernel $(rust_os) $(assembly_object_files) $(linker_script)
	@ld -n -T $(linker_script) -o $(kernel) \
		$(assembly_object_files) $(rust_os)

	@RUST_TARGET_PATH=$(shell pwd) xargo build --target $(target)

We add a new kernel target that just executes xargo build and modify the $(kernel) target to link the created static lib. We also add the new kernel target to the .PHONY list, since it does not belong to a file with that name.

But now xargo build is executed on every make, even if no source file was changed. And the ISO is recreated on every make iso/make run, too. We could try to avoid this by adding dependencies on all rust source and cargo configuration files to the kernel target, but the ISO creation takes only half a second on my machine and most of the time we will have changed a Rust file when we run make. So we keep it simple for now and let cargo do the bookkeeping of changed files (it does it anyway).

🔗Calling Rust

Now we can call the main method in long_mode_start:

bits 64

    ; call the rust main
    extern rust_main     ; new
    call rust_main       ; new

    ; print `OKAY` to screen
    mov rax, 0x2f592f412f4b2f4f
    mov qword [0xb8000], rax

By defining rust_main as extern we tell nasm that the function is defined in another file. As the linker takes care of linking them together, we’ll get a linker error if we have a typo in the name or forget to mark the rust function as pub extern.

If we’ve done everything right, we should still see the green OKAY when executing make run. That means that we successfully called the Rust function and returned back to assembly.

🔗Fixing Linker Errors

Now we can try some Rust code:

pub extern fn rust_main() {
    let x = ["Hello", "World", "!"];
    let y = x;

When we test it using make run, it fails with undefined reference to 'memcpy'. The memcpy function is one of the basic functions of the C library (libc). Usually the libc crate is linked to every Rust program together with the standard library, but we opted out through #![no_std]. We could try to fix this by adding the libc crate as extern crate. But libc is just a wrapper for the system libc, for example glibc on Linux, so this won’t work for us. Instead we need to recreate the basic libc functions such as memcpy, memmove, memset, and memcmp in Rust.


Fortunately there already is a crate for that: rlibc. When we look at its source code we see that it contains no magic, just some raw pointer operations in a while loop. To add rlibc as a dependency we just need to add two lines to the Cargo.toml:

rlibc = "1.0"

and an extern crate definition in our src/lib.rs:

extern crate rlibc;

pub extern fn rust_main() {

Now make run doesn’t complain about memcpy anymore. Instead it will show a pile of new ugly linker errors:

    In function `_$LT$f32$u20$as$u20$core..num..dec2flt..
    undefined reference to `__floatundisf'
    In function `_$LT$f64$u20$as$u20$core..num..dec2flt..rawfp..
    undefined reference to `__floatundidf'
    In function `core::num::from_str_radix::h09b12650704e0508':
    undefined reference to `__muloti4'


The new errors are linker errors about various missing functions such as __floatundisf or __muloti4. These functions are part of LLVM’s compiler-rt builtins and are normally linked by the standard library. For no_std crates like ours, one has to link the compiler-rt library manually. Unfortunately, this library is implemented in C and the build process is a bit cumbersome. Alternatively, there is the compiler-builtins crate that tries to port the library to Rust, but it isn’t complete yet.

In our case, there is a much simpler solution, since our kernel doesn’t really need any of those functions yet. So we can just tell the linker to remove unused program sections and hopefully all references to these functions will disappear. Removing unused sections is generally a good idea as it reduces kernel size. The magic linker flag for this is --gc-sections, which stands for “garbage collect sections”. Let’s add it to the $(kernel) target in our Makefile:

$(kernel): xargo $(rust_os) $(assembly_object_files) $(linker_script)
	@ld -n --gc-sections -T $(linker_script) -o $(kernel) \
		$(assembly_object_files) $(rust_os)

Now we can do a make run again and it compiles without errors again. However, it doesn’t boot anymore:

GRUB error: no multiboot header found.

What happened? Well, the linker removed unused sections. And since we don’t use the Multiboot section anywhere, ld removes it, too. So we need to tell the linker explicitly that it should keep this section. The KEEP command does exactly that, so we add it to the linker script (linker.ld):

.boot :
    /* ensure that the multiboot header is at the beginning */

Now everything should work again (the green OKAY). But there is another linking issue, which is triggered by some other example code.

🔗panic = “abort”

The following snippet still fails:

    let test = (0..3).flat_map(|x| 0..x).zip(0..);

The error is a linker error again (hence the ugly error message):

    In function `core::ptr::drop_in_place<core::iter::Zip<
        core::iter::FlatMap<core::ops::Range<i32>, core::ops::Range<i32>,
        closure>, core::ops::RangeFrom<i32>>>':
    undefined reference to `_Unwind_Resume'
    In function `core::iter::iterator::Iterator::zip<core::iter::FlatMap<
        core::ops::Range<i32>, core::ops::Range<i32>, closure>,
    undefined reference to `_Unwind_Resume'

So the linker can’t find a function named _Unwind_Resume that is referenced e.g. in iter/iterator.rs:389 in libcore. This reference is not really there at line 389 of libcore’s iterator.rs. Instead, it is a compiler inserted landing pad, which is used for panic handling.

By default, the destructors of all stack variables are run when a panic occurs. This is called unwinding and allows parent threads to recover from panics. However, it requires a platform specific gcc library, which isn’t available in our kernel.

Fortunately, Rust allows us to disable unwinding for our target. For that we add the following line to our x86_64-blog_os.json file:

  "panic-strategy": "abort"

By setting the panic strategy to abort instead of the default unwind, we disable all unwinding in our kernel. Let’s try make run again:

   Compiling core v0.0.0 (file:///…/rust/src/libcore)
    Finished release [optimized] target(s) in 22.24 secs
    Finished dev [unoptimized + debuginfo] target(s) in 0.5 secs
    In function `core::ptr::drop_in_place<…>':
    undefined reference to `_Unwind_Resume'

We see that xargo recompiles the core crate, but the _Unwind_Resume error still occurs. This is because our blog_os crate was not recompiled somehow and thus still references the unwinding function. To fix this, we need to force a recompile using cargo clean:

> cargo clean
> make run
   Compiling rlibc v1.0.0
   Compiling blog_os v0.1.0 (file:///home/philipp/Documents/blog_os/tags)
warning: unused variable: `test` […]

    Finished dev [unoptimized + debuginfo] target(s) in 0.60 secs

It worked! We no longer see linker errors and our kernel prints OKAY again.

🔗Hello World!

Finally, it’s time for a Hello World! from Rust:

pub extern fn rust_main() {
    // ATTENTION: we have a very small stack and no guard page

    let hello = b"Hello World!";
    let color_byte = 0x1f; // white foreground, blue background

    let mut hello_colored = [color_byte; 24];
    for (i, char_byte) in hello.into_iter().enumerate() {
        hello_colored[i*2] = *char_byte;

    // write `Hello World!` to the center of the VGA text buffer
    let buffer_ptr = (0xb8000 + 1988) as *mut _;
    unsafe { *buffer_ptr = hello_colored };


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.

🔗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.

Comments (Archived)


If you decide to add interrupt support to your OS (for keyboard input, for example), you may not want Rust to be generating SSE code. If you use SEE code in the kernel, then you need to save SSE registers in interrupts, and saving SSE registers is slow and takes a lot of RAM. As far as I can tell, a lot of kernels simply avoid floating point to help keep interrupts and system calls efficient.

Also, as you noted in your bug on GitHub, you'll also want to set no-redzone to prevent memory corruption during interrupts.

Since we need to set a bunch of compiler flags for all generated code, including libcore, the right answer may be to replace the target x86_64-unknown-linux-gnu with a custom target that uses the right options by default. There's a discussion here and an example target file in the zinc OS.


OK, it took almost a day, but I think I've got this figured out. This is probably overkill for your great blog posts, but I'll leave it here for the next person to pass this way.

Here's the basic strategy to getting an SSE-free, redzone-free kernel:

1. Define a new target x86_64-unknown-none-gnu, where none means running on bare metal without an OS. This can be done by creating a file x86_64-unknown-none-gnu.json and filling it in with the right options. See below. You can just drop this in your top-level build directory and Rust will find it.

2. Check out the same Rust you're compiling with, and patch libcore to remove floating point. You can usually find a current libcore patch in thepowersgang/rust-barebones-kernel on GitHub.

3. Build libcore with --target $(target) --cfg disable_float, and put it in ~/.multirust/toolchains/nightly/lib/rustlib/$(target)/lib.

4. Run cargo normally, specifying your custom target with --target $(target).

Here's my custom x86_64-unknown-none-gnu.json file

"llvm-target": "x86_64-unknown-none-gnu",
"target-endian": "little",
"target-pointer-width": "64",
"os": "none",
"arch": "x86_64",
"data-layout": "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128",
"pre-link-args": [ "-m64" ],
"cpu": "x86-64",
"features": "-mmx,-sse,-sse2,-sse3,-ssse3",
"disable-redzone": true,
"eliminate-frame-pointer": false,
"linker-is-gnu": true,
"no-compiler-rt": true,
"archive-format": "gnu"

This seems like a good approach, because I'm not compiling Rust code for the Linux user-space, and then trying to convince it to run on bare metal. Instead, I'm compiling Rust code against a properly-configured bare metal target, and if I don't like the compiler options, I can quickly change them for all crates. And if any floating point code tries to sneak into kernel space, I'll get an error immediately, instead of finding it when floating point registers get clobbered by an interrupt that used MMX code.

The osdev wiki claims that this the harder but wiser course of action:

Common examples [of beginner mistakes] include being too lazy to use a Cross-Compiler, developing in Real Mode instead of Protected Mode or Long Mode, relying on BIOS calls rather than writing real hardware drivers, using flat binaries instead of ELF, and so on.

Since they know way more about this than I do, I'm going with their suggestions for now. :-)

Philipp Oppermann

Why does your target.json file include

"features": "-mmx,-sse,-sse2,-sse3,-ssse3"

And doesn't Rust use the `xmm` registers to optimize non-floating-point code, too?


In theory, "-mmx" means "disable mmx", and so on. I'm attempting to convince Rust and LLVM to leave all those registers alone in kernel space, and to never generate any code which uses them. The goal here is not to need to save that huge block of registers (plus FPU state) on every interrupt. This seems to be a popular choice for x86 kernels.

Does it work? We'll see.

Philipp Oppermann

Ah, I see... It seems like there is no documentation about this. Hopefully the libcore-without-sse issue gets resolved soon. Manually patching libcore seems like a really ugly solution.

I think I will choose the "slow" solution and just save the sse registers on every interrupt. It's required anyway when switching between (user) processes.

In my opinion the best solution would be an annotation to disable SSE just for the interrupt handlers.

Alister Lee

This is currently also hard on ARM, because I can't work out the features to disable to avoid emitting fpu instructions. I've raised a bug on llvm to seek clarification: https://llvm.org/bugs/show_...


Thanks heaps Phil. Just a comment for others that the rlib dependency strategy you describe won't work under a cross-compiling (ie. arm / r-pi) because the multirust nightly won't include the libcore necessary for the dependant crates to build, and they won't refer to the ones inside /target. See here: https://github.com/rust-lan...

Alister Lee

Right, have learned a lot in the last month, following you on ARM. I expect I'll need rlibc, but I haven't yet.

What I have needed is `compiler-rt`, which you have avoided because you are building on a (tier 3) supported build target which is [not the case](http://stackoverflow.com/qu...) for `arm-none-eabi`.

Philipp Oppermann

You can avoid compiler-rt by using a custom target file that contains `"no-compiler-rt": true`.

You can then use nightly-libcore to cross compile libcore for your new target.


For OS X/Darwin users who have made it this far:


It's been a good run, but Apple's modifications to clang and ld for the Darwin system completely destroy rust's existing cross-compile capabilities, which means building an x86_64-compatibile libcore simply isn't possible without monumental amounts of work.

Aaron D

You might want to try again, I've been following along with all of the latest posts on macOS 10.11 without problems.

Doesn't the linker problem still exist? Most of the options used by GNU 'ld' are not supported by macOS 10.11 'ld'. May be you used cross compiled 'ld' ?

Jeff Westfahl

I guess there's a reason you can't enable SSE in your 32-bit assembly file before you switch to long mode?

Philipp Oppermann

It should be totally possible to do it in the 32-bit file. I just tested it and it works without problems. I think I used to do more things in the `long_mode_init` file in a previous system so that there was already an error function. But since it's now the only function that needs the 64-bit error function, we could remove that function if we moved the `setup_SEE` function.

Thanks for the hint! I opened an issue for this.

stephane geneix

on my box, I couldn't reproduce the SSE error. It looks like "a += 1;" doesn't generate SSE instructions anymore by default.

objdump still shows some in what looks like exception handling code but seems to never execute
~/dev/rustOS/$rustc --version
rustc 1.7.0-nightly (81dd3824f 2015-12-11)
~/dev/rustOS/$cargo --version
cargo 0.8.0-nightly (028ac34 2015-12-10)

Thank you very much for this series though, it's probably one of the most interesting ways I've seen to learn about OS boot sequence I've seen

Philipp Oppermann

Thanks a lot! I opened an issue for this.

How about the following example?:

let mut a = ("hello", 42);
a.1 += 1;

stephane geneix

yes, that one breaks down without SSE

Philipp Oppermann

Perfect! I will update it


so much fun ! Thanks for this 💥🍾🍻 ! Can we have a emoji Hello World ? Just kidding.

Philipp Oppermann

Actually there are two smileys in code page 437.

Smiley Hello World:

let hello = b"\x02\x01 Hello World! \x01\x02";
let color_byte = 0x1f;

let mut hello_colored = [color_byte; 36];


omg. this is brilliant, almost forgot about these (ascii?) codes. Thanks !

Aleksey Kladov

Awesome! I've made a buffer overrun error, because I've added a comma to the "Hello, World!", and Rust have actually caught it at run time, and started looping.


#[lang = "panic_fmt" ]
extern fn panic_fmt() -> ! {
let buffer_ptr = (0xb8000) as *mut _;
let red = 0x4f;
unsafe {
*buffer_ptr = [b'P', red, b'a', red, b'n', red, b'i', red, b'c', red, b'!', red];
loop { }

Helped a lot.


Using the most recent nightly build for this, the no-landing-pads snippet also generates SSE, so it's a bit of a two-for-one. :)

Philipp Oppermann

Thanks a lot! I fixed it by removing the superfluous let mut a = ("hello", 42); a.1 += 1; snippet (see PR #153).


I think that libcore needs both SSE and SSE2 to be supported. Shouldn't you check the SSE2 CPUID flag to be sure that both SSE and SSE2 is present? Not sure if it could cause any problems within libcore later on

Philipp Oppermann

Good catch! However, SSE2 should always be available if the long mode is available. Citing the OSDev wiki:

When the X86-64 architecture was introduced, AMD demanded a minimum level of SSE support to simplify OS code. Any system capable of long mode should support at least SSE and SSE2

So SSE and SSE2 should always be available in our case (if the wiki is correct). So we could even remove the SSE check. However, I think it's better to leave it in, because we enable SSE before switching to long mode.

Don Rowe

Thanks again for sharing this! FYI, the link https://doc.rust-lang.org/std/rt/unwind/ in http://os.phil-opp.com/set-... is broken.

Philipp Oppermann

Thanks! I've fixed it in #207.

Sorry for the delay, your comment got buried in my inbox somehow…


If you want text that is moving around the screen like a snake, get that code and replace you rust_main function with it:

pub extern fn rust_main() {

let color_byte: u16 = 0x1f;
let ascii_byte: u16 = 32;
let empty_2byte_character: u16 = (color_byte << 8) | ascii_byte;

let mut poz = 0;
while poz < 4000
let buffer = (0xb8000 + poz ) as *mut _;
unsafe{*buffer = empty_2byte_character };

let text = b"ANIMATED TEXT!!!! ->";
let color_byte = 0x1f;

let mut text_colored = [color_byte; 44];
for(i, char_byte) in text.into_iter().enumerate(){
text_colored[i*2] = *char_byte;

let mut offset = 0;
let mut done = false;
let mut delay_counter = 0;

while !done
let poprzedni = (0xb8000 + offset) as *mut _;
unsafe{*poprzedni = empty_2byte_character };


let buffer_ptr = (0xb8000 + offset) as *mut _;
unsafe{*buffer_ptr = text_colored };

if offset == (4000-44)
done = true;
while delay_counter < 10000000
delay_counter = 0;




Aaron D

With the latest rust nightly I was getting linker errors after pulling in in the rlibc crate:

target/x86_64-unknown-linux-gnu/debug/libblog_os.a(core-93f19628b61beb76.0.o): In function `core::panicking::panic_fmt':
/buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libcore/panicking.rs:69: undefined reference to `rust_begin_unwind'
make: *** [build/kernel-x86_64.bin] Error 1

Apparently the later versions of the compiler are pretty strict about mangling almost anything they can for optimization. Usually the panic_fmt symbol becomes rust_begin_unwind (for some reason), but now it's getting mangled and so the linker can't find that symbol - it's a pretty cryptic error with discussion at https://github.com/rust-lan...

To fix it, you need to mark panic_fmt with no_mangle as well, so the line in lib.rs becomes:
#[lang = "panic_fmt"] #[no_mangle] extern fn panic_fmt() -> ! {loop{}}

This allows it to build properly.


Thank you for that!


Hello, I have reached the stage of panic = "abort", but when I make run I get this error: target/x86_64-os/debug/libos.a(core-9a5ada2b08448709.0.o): In function core::panicking::panic_fmt': core.cgu-0.rs:(.text.cold._ZN4core9panicking9panic_fmt17h6b6d64bae0e8a2c2E+0x88): undefined reference torust_begin_unwind', I really have no clue what is happening here as I have exactly the same code as you do above.

EDIT: I have read some of the above comments, turns out that other people were having the same issue as me and I have used their solutions. Sorry to waste your time.


There is an error when changing the makefile(roughly in the middle of this post). This part

which stands for “garbage collect sections”. Let's add it to the $(kernel) target in our Makefile: $(kernel): xargo $(rust_os) $(assembly_object_files) $(linker_script) @ld -n --gc-sections -T $(linker_script) -o $(kernel) \ $(assembly_object_files) $(rust_os)

results in "no rule to make target 'xargo'

when changing it to this it works again:

$(kernel): kernel $(rust_os) $(assembly_object_files) $(linker_script) @ld -n --gc-sections -T $(linker_script) -o $(kernel) \ $(assembly_object_files) $(rust_os)

Hey, loving the tutorials :) though I'm running into an issue when using xargo build. When I do xargo build --target=x86_64-blog_os, I get the following error:

error: failed to parse manifest at '/home/max/TesterOS/src/Cargo.toml'

caused by: can't find library 'blog_os', rename file to 'src/lib.rs' or specify lib.path

Could this be because of where I've saved my files? Because when I saw src/lib.rs in the tutorial, I just saved lib.rs in the src file we created. Is it something to do with where I placed my Cargo.toml or/and x86_64-blog_os.json file?

Really confused here.

Philipp Oppermann

Cargo assumes that the lib.rs file is in a subfolder named src. So it doesn't work if you put the lib.rs next to the Cargo.toml.

Thanks a million, it's all sorted now :). One more issue though. About the rlibc... make run seems to work fine without extern crate rlibc... But fails when I do add it in, saying it can't compile rlibc.

Sorry to be a bother lol I'm a newb.

Philipp Oppermann

There is currently a problem with cargo/xargo, maybe this is affects you: https://github.com/phil-opp/blog_os/issues/379