get basic no_std example to build

This commit is contained in:
ahgamut 2022-06-21 12:39:00 +05:30
parent 5a60117dec
commit c504f3e9c6
7 changed files with 240 additions and 0 deletions

7
.gitignore vendored
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# ignore built APE and debug executables
*.com
*.com.dbg
# download cosmo amalgamation
/libcosmo/*
!/libcosmo/README.md
# Generated by Cargo # Generated by Cargo
# will have compiled files and executables # will have compiled files and executables
/target/ /target/

8
Cargo.toml Normal file
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[package]
name = "hello_world"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]

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README.md Normal file
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# Actually Portable Executables with Cosmopolitan Libc and Rust
This repository contains a simple `Hello world!` example in the [Rust][rust]
programming language, that builds with [Cosmopolitan Libc][cosmo].
I created a [custom compilation target][custom-target] for Rust, called
`x86_64-unknown-linux-cosmo`, to provide a build process the Cosmopolitan Libc
amalgamation and `cargo`. I followed the documentation in the [Rust
Embedonomicon][custom-embed] to create the target.
An alternative method to build APEs with Rust would be to avoid `cargo`, just
use `rustc` or equivalent compiler to generate `.o` files, and then write a
shell script that does the linking with the expected flags. I have not tried
this method.
## Build steps
1. Download the Cosmopolitan Libc [amalgamation][amalg-download] into the `libcosmo` folder:
```bash
cd libcosmo
wget https://justine.lol/cosmopolitan/cosmopolitan.zip
unzip cosmopolitan.zip
cd ../
```
2. Download the necessary toolchain(s) and source code for Rust:
```bash
rustup toolchain install nightly-x86_64-unknown-linux-gnu
rustup component add rust-src --toolchain nightly-x86_64-unknown-linux-gnu
```
3. run `cargo build` to get the debug executable. This uses a bash script that
removes unnecessary linker arguments. A recent version of `gcc` and `ld.bfd`
is required.
```bash
cargo +nightly build -Zbuild-std=core,libc --target=./x86_64-unknown-linux-cosmo.json
```
4. run `objcopy` on the debug binary to obtain the APE:
```bash
objcopy -SO binary ./target/x86_64-unknown-linux-cosmo/debug/hello_world.com.dbg ./hello_world.com
```
## What about the `std` crate?
The `std` crate compiles successfully, but fails at the linker stage. Here's how
that can be tested:
1. Change the source code in `src/main.rs` to use the commented out `main`
function and `#![restricted_std]`.
2. In the source code for Rust's `std` crate, change a `cfg_if` in
`$HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/backtrace/src/backtrace/mod.rs`
to not use the `noop` trace instead of depending on `libunwind`.
```diff
--- mod.rs 2022-06-21 12:52:21.724053459 +0530
+++ mod.rs 2022-06-21 13:05:50.948777093 +0530
@@ -132,7 +132,7 @@
pub(crate) mod miri;
use self::miri::trace as trace_imp;
pub(crate) use self::miri::Frame as FrameImp;
- } else if #[cfg(
+ } /* else if #[cfg(
any(
all(
unix,
@@ -154,7 +154,7 @@
pub(crate) use self::dbghelp::Frame as FrameImp;
#[cfg(target_env = "msvc")] // only used in dbghelp symbolize
pub(crate) use self::dbghelp::StackFrame;
- } else {
+ } */ else {
mod noop;
use self::noop::trace as trace_imp;
pub(crate) use self::noop::Frame as FrameImp;
```
I haven't figured out what config I should give to `cargo` so I don't need to do
this. I find it surprising that `std` cannot be built without relying on
`libunwind`.
3. The build command now changes to
```bash
cargo +nightly build -Zbuild-std=core,alloc,panic_abort,libc,std -Zbuild-std-features= --target=./x86_64-unknown-linux-cosmo.json
```
4. At the linker stage you might find some of the following symbols are missing:
- If `Unwind_Backtrace` or similar is missing, you need to check if step 2 is
done properly.
- `open64`, `stat64`, `fstat64`, `__xpg_strerror_r`: these can be added to
Cosmopolitan Libc via aliases of the existing functions.
- `pthread_key_create`,`pthread_setspecific`,`pthread_key_delete`,`pthread_getspecific`
-- these functions should not be needed in a single-threaded program, but
somehow they are still linked. Support for threads is currently being added
to Cosmopolitan Libc, but possibly the related code in the `std` crate can
be changed to avoid this issue.
[rust]: https://rust-lang.org
[cosmo]: https://github.com/jart/cosmopolitan
[amalg-download]: https://justine.lol/cosmopolitan/download.html
[custom-target]: https://doc.rust-lang.org/rustc/targets/custom.html
[custom-embed]: https://docs.rust-embedded.org/embedonomicon/custom-target.html

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gcc-linker-wrapper.bash Executable file
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#!/bin/bash
set -eu
declare -a args
args=()
for o in "$@" ; do
case $o in
"-lunwind") continue;;
"-lutil") continue;;
"-lrt") continue;;
"-lc") continue;;
"-lm") continue;;
"-lpthread") continue;;
"-lgcc") continue;;
"-Wl,-Bdynamic") continue;;
"-Wl,-Bstatic") continue;;
esac
args+=("$o")
done
gcc "${args[@]}"

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libcosmo/README.md Normal file
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src/main.rs Normal file
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#![no_main]
#![no_std]
#![feature(rustc_private)]
extern crate libc;
#[no_mangle]
pub extern "C" fn main(_argc: isize, _argv: *const *const u8) -> isize {
// Since we are passing a C string the final null character is mandatory
const HELLO: &'static str = "Hello, world! %d + %d = %d\n\0";
let x: i32 = 1;
let y: i32 = 2;
unsafe {
libc::printf(HELLO.as_ptr() as *const _, x, y, x+y);
}
0
}
#[panic_handler]
fn my_panic(_info: &core::panic::PanicInfo) -> ! {
loop {}
}
/* std crate requires some external changes
#![feature(restricted_std)]
pub fn main() {
println!("hello pls cosmo rust APE");
}
*/

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{
"llvm-target": "x86_64-unknown-linux-musl",
"target-pointer-width": "64",
"arch": "x86_64",
"data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128",
"cpu": "x86-64",
"os":"linux",
"env": "musl",
"panic-strategy":"abort",
"requires-uwtable":false,
"dynamic-linking": false,
"executables": true,
"exe-suffix": ".com.dbg",
"emit-debug-gdb-scripts":false,
"crt-static-default": true,
"crt-static-respected": false,
"linker-is-gnu":true,
"allows-weak-linkage":true,
"has-rpath": false,
"has-thread-local": false,
"is-builtin": false,
"trap-unreachable":true,
"position-independent-executables": false,
"static-position-independent-executables": false,
"relocation-model": "static",
"disable-redzone":true,
"frame-pointer":"always",
"requires-lto":false,
"eh-frame-header":false,
"no-default-libraries":true,
"max-atomic-width":64,
"linker-flavor":"gcc",
"linker": "./gcc-linker-wrapper.bash",
"late-link-args": {
"gcc": []
},
"pre-link-args": {
"gcc": [
"-static",
"-nostdinc",
"-nostdlib",
"-pg",
"-mnop-mcount"
]
},
"post-link-args": {
"gcc": [
"-Wl,--gc-sections",
"-fuse-ld=bfd",
"-Wl,-T,./libcosmo/ape.lds",
"./libcosmo/crt.o",
"./libcosmo/ape-no-modify-self.o",
"./libcosmo/cosmopolitan.a"
]
},
"stack-probes": {
"kind": "none"
},
"target-family": [
"unix"
]
}