// SPDX-License-Identifier: GPL-2.0
//! The custom target specification file generator for `rustc`.
//!
//! To configure a target from scratch, a JSON-encoded file has to be passed
//! to `rustc` (introduced in [RFC 131]). These options and the file itself are
//! unstable. Eventually, `rustc` should provide a way to do this in a stable
//! manner. For instance, via command-line arguments. Therefore, this file
//! should avoid using keys which can be set via `-C` or `-Z` options.
//!
//! [RFC 131]: https://rust-lang.github.io/rfcs/0131-target-specification.html
use std::{
collections::HashMap,
fmt::{Display, Formatter, Result},
io::BufRead,
};
enum Value {
Boolean(bool),
Number(i32),
String(String),
Array(Vec<Value>),
Object(Object),
}
type Object = Vec<(String, Value)>;
fn comma_sep<T>(
seq: &[T],
formatter: &mut Formatter<'_>,
f: impl Fn(&mut Formatter<'_>, &T) -> Result,
) -> Result {
if let [ref rest @ .., ref last] = seq[..] {
for v in rest {
f(formatter, v)?;
formatter.write_str(",")?;
}
f(formatter, last)?;
}
Ok(())
}
/// Minimal "almost JSON" generator (e.g. no `null`s, no escaping),
/// enough for this purpose.
impl Display for Value {
fn fmt(&self, formatter: &mut Formatter<'_>) -> Result {
match self {
Value::Boolean(boolean) => write!(formatter, "{}", boolean),
Value::Number(number) => write!(formatter, "{}", number),
Value::String(string) => write!(formatter, "\"{}\"", string),
Value::Array(values) => {
formatter.write_str("[")?;
comma_sep(&values[..], formatter, |formatter, v| v.fmt(formatter))?;
formatter.write_str("]")
}
Value::Object(object) => {
formatter.write_str("{")?;
comma_sep(&object[..], formatter, |formatter, v| {
write!(formatter, "\"{}\": {}", v.0, v.1)
})?;
formatter.write_str("}")
}
}
}
}
impl From<bool> for Value {
fn from(value: bool) -> Self {
Self::Boolean(value)
}
}
impl From<i32> for Value {
fn from(value: i32) -> Self {
Self::Number(value)
}
}
impl From<String> for Value {
fn from(value: String) -> Self {
Self::String(value)
}
}
impl From<&str> for Value {
fn from(value: &str) -> Self {
Self::String(value.to_string())
}
}
impl From<Object> for Value {
fn from(object: Object) -> Self {
Self::Object(object)
}
}
impl<T: Into<Value>, const N: usize> From<[T; N]> for Value {
fn from(i: [T; N]) -> Self {
Self::Array(i.into_iter().map(|v| v.into()).collect())
}
}
struct TargetSpec(Object);
impl TargetSpec {
fn new() -> TargetSpec {
TargetSpec(Vec::new())
}
fn push(&mut self, key: &str, value: impl Into<Value>) {
self.0.push((key.to_string(), value.into()));
}
}
impl Display for TargetSpec {
fn fmt(&self, formatter: &mut Formatter<'_>) -> Result {
// We add some newlines for clarity.
formatter.write_str("{\n")?;
if let [ref rest @ .., ref last] = self.0[..] {
for (key, value) in rest {
write!(formatter, " \"{}\": {},\n", key, value)?;
}
write!(formatter, " \"{}\": {}\n", last.0, last.1)?;
}
formatter.write_str("}")
}
}
struct KernelConfig(HashMap<String, String>);
impl KernelConfig {
/// Parses `include/config/auto.conf` from `stdin`.
fn from_stdin() -> KernelConfig {
let mut result = HashMap::new();
let stdin = std::io::stdin();
let mut handle = stdin.lock();
let mut line = String::new();
loop {
line.clear();
if handle.read_line(&mut line).unwrap() == 0 {
break;
}
if line.starts_with('#') {
continue;
}
let (key, value) = line.split_once('=').expect("Missing `=` in line.");
result.insert(key.to_string(), value.trim_end_matches('\n').to_string());
}
KernelConfig(result)
}
/// Does the option exist in the configuration (any value)?
///
/// The argument must be passed without the `CONFIG_` prefix.
/// This avoids repetition and it also avoids `fixdep` making us
/// depend on it.
fn has(&self, option: &str) -> bool {
let option = "CONFIG_".to_owned() + option;
self.0.contains_key(&option)
}
}
fn main() {
let cfg = KernelConfig::from_stdin();
let mut ts = TargetSpec::new();
// `llvm-target`s are taken from `scripts/Makefile.clang`.
if cfg.has("ARM64") {
panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
} else if cfg.has("RISCV") {
if cfg.has("64BIT") {
panic!("64-bit RISC-V uses the builtin rustc riscv64-unknown-none-elf target");
} else {
panic!("32-bit RISC-V is an unsupported architecture");
}
} else if cfg.has("X86_64") {
ts.push("arch", "x86_64");
ts.push(
"data-layout",
"e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
);
let mut features = "-mmx,+soft-float".to_string();
if cfg.has("MITIGATION_RETPOLINE") {
// The kernel uses `-mretpoline-external-thunk` (for Clang), which Clang maps to the
// target feature of the same name plus the other two target features in
// `clang/lib/Driver/ToolChains/Arch/X86.cpp`. These should be eventually enabled via
// `-Ctarget-feature` when `rustc` starts recognizing them (or via a new dedicated
// flag); see https://github.com/rust-lang/rust/issues/116852.
features += ",+retpoline-external-thunk";
features += ",+retpoline-indirect-branches";
features += ",+retpoline-indirect-calls";
}
if cfg.has("MITIGATION_SLS") {
// The kernel uses `-mharden-sls=all`, which Clang maps to both these target features in
// `clang/lib/Driver/ToolChains/Arch/X86.cpp`. These should be eventually enabled via
// `-Ctarget-feature` when `rustc` starts recognizing them (or via a new dedicated
// flag); see https://github.com/rust-lang/rust/issues/116851.
features += ",+harden-sls-ijmp";
features += ",+harden-sls-ret";
}
ts.push("features", features);
ts.push("llvm-target", "x86_64-linux-gnu");
ts.push("supported-sanitizers", ["kcfi", "kernel-address"]);
ts.push("target-pointer-width", "64");
} else if cfg.has("X86_32") {
// This only works on UML, as i386 otherwise needs regparm support in rustc
if !cfg.has("UML") {
panic!("32-bit x86 only works under UML");
}
ts.push("arch", "x86");
ts.push(
"data-layout",
"e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128",
);
let mut features = "-mmx,+soft-float".to_string();
if cfg.has("MITIGATION_RETPOLINE") {
features += ",+retpoline-external-thunk";
}
ts.push("features", features);
ts.push("llvm-target", "i386-unknown-linux-gnu");
ts.push("target-pointer-width", "32");
} else if cfg.has("LOONGARCH") {
panic!("loongarch uses the builtin rustc loongarch64-unknown-none-softfloat target");
} else {
panic!("Unsupported architecture");
}
ts.push("emit-debug-gdb-scripts", false);
ts.push("frame-pointer", "may-omit");
ts.push(
"stack-probes",
vec![("kind".to_string(), Value::String("none".to_string()))],
);
// Everything else is LE, whether `CPU_LITTLE_ENDIAN` is declared or not
// (e.g. x86). It is also `rustc`'s default.
if cfg.has("CPU_BIG_ENDIAN") {
ts.push("target-endian", "big");
}
println!("{}", ts);
}
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