1
linux/scripts/generate_rust_target.rs

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Rust
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// 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",
rust: upgrade to Rust 1.78.0 This is the next upgrade to the Rust toolchain, from 1.77.1 to 1.78.0 (i.e. the latest) [1]. See the upgrade policy [2] and the comments on the first upgrade in commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2"). It is much smaller than previous upgrades, since the `alloc` fork was dropped in commit 9d0441bab775 ("rust: alloc: remove our fork of the `alloc` crate") [3]. # Unstable features There have been no changes to the set of unstable features used in our own code. Therefore, the only unstable features allowed to be used outside the `kernel` crate is still `new_uninit`. However, since we finally dropped our `alloc` fork [3], all the unstable features used by `alloc` (~30 language ones, ~60 library ones) are not a concern anymore. This reduces the maintenance burden, increases the chances of new compiler versions working without changes and gets us closer to the goal of supporting several compiler versions. It also means that, ignoring non-language/library features, we are currently left with just the few language features needed to implement the kernel `Arc`, the `new_uninit` library feature, the `compiler_builtins` marker and the few `no_*` `cfg`s we pass when compiling `core`/`alloc`. Please see [4] for details. # Required changes ## LLVM's data layout Rust 1.77.0 (i.e. the previous upgrade) introduced a check for matching LLVM data layouts [5]. Then, Rust 1.78.0 upgraded LLVM's bundled major version from 17 to 18 [6], which changed the data layout in x86 [7]. Thus update the data layout in our custom target specification for x86 so that the compiler does not complain about the mismatch: error: data-layout for target `target-5559158138856098584`, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128`, differs from LLVM target's `x86_64-linux-gnu` default layout, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128` In the future, the goal is to drop the custom target specifications. Meanwhile, if we want to support other LLVM versions used in `rustc` (e.g. for LTO), we will need to add some extra logic (e.g. conditional on LLVM's version, or extracting the data layout from an existing built-in target specification). ## `unused_imports` Rust's `unused_imports` lint covers both unused and redundant imports. Now, in 1.78.0, the lint detects more cases of redundant imports [8]. Thus one of the previous patches cleaned them up. ## Clippy's `new_without_default` Clippy now suggests to implement `Default` even when `new()` is `const`, since `Default::default()` may call `const` functions even if it is not `const` itself [9]. Thus one of the previous patches implemented it. # Other changes in Rust Rust 1.78.0 introduced `feature(asm_goto)` [10] [11]. This feature was discussed in the past [12]. Rust 1.78.0 introduced `feature(const_refs_to_static)` [13] to allow referencing statics in constants and extended `feature(const_mut_refs)` to allow raw mutable pointers in constants. Together, this should cover the kernel's `VTABLE` use case. In fact, the implementation [14] in upstream Rust added a test case for it [15]. Rust 1.78.0 with debug assertions enabled (i.e. `-Cdebug-assertions=y`, kernel's `CONFIG_RUST_DEBUG_ASSERTIONS=y`) now always checks all unsafe preconditions, though without a way to opt-out for particular cases [16]. It would be ideal to have a way to selectively disable certain checks per-call site for this one (i.e. not just per check but for particular instances of a check), even if the vast majority of the checks remain in place [17]. Rust 1.78.0 also improved a couple issues we reported when giving feedback for the new `--check-cfg` feature [18] [19]. # `alloc` upgrade and reviewing As mentioned above, compiler upgrades will not update `alloc` anymore, since we dropped our `alloc` fork [3]. Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1780-2024-05-02 [1] Link: https://rust-for-linux.com/rust-version-policy [2] Link: https://lore.kernel.org/rust-for-linux/20240328013603.206764-1-wedsonaf@gmail.com/ [3] Link: https://github.com/Rust-for-Linux/linux/issues/2 [4] Link: https://github.com/rust-lang/rust/pull/120062 [5] Link: https://github.com/rust-lang/rust/pull/120055 [6] Link: https://reviews.llvm.org/D86310 [7] Link: https://github.com/rust-lang/rust/pull/117772 [8] Link: https://github.com/rust-lang/rust-clippy/pull/10903 [9] Link: https://github.com/rust-lang/rust/pull/119365 [10] Link: https://github.com/rust-lang/rust/issues/119364 [11] Link: https://lore.kernel.org/rust-for-linux/ZWipTZysC2YL7qsq@Boquns-Mac-mini.home/ [12] Link: https://github.com/rust-lang/rust/issues/119618 [13] Link: https://github.com/rust-lang/rust/pull/120932 [14] Link: https://github.com/rust-lang/rust/pull/120932/files#diff-e6fc1622c46054cd46b1d225c5386c5554564b3b0fa8a03c2dc2d8627a1079d9 [15] Link: https://github.com/rust-lang/rust/issues/120969 [16] Link: https://github.com/Rust-for-Linux/linux/issues/354 [17] Link: https://github.com/rust-lang/rust/pull/121202 [18] Link: https://github.com/rust-lang/rust/pull/121237 [19] Reviewed-by: Alice Ryhl <aliceryhl@google.com> Link: https://lore.kernel.org/r/20240401212303.537355-4-ojeda@kernel.org [ Added a few more details and links I mentioned in the list. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-04-01 14:23:03 -07:00
"e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
);
rust: x86: remove `-3dnow{,a}` from target features LLVM 19 is dropping support for 3DNow! in commit f0eb5587ceeb ("Remove support for 3DNow!, both intrinsics and builtins. (#96246)"): Remove support for 3DNow!, both intrinsics and builtins. (#96246) This set of instructions was only supported by AMD chips starting in the K6-2 (introduced 1998), and before the "Bulldozer" family (2011). They were never much used, as they were effectively superseded by the more-widely-implemented SSE (first implemented on the AMD side in Athlon XP in 2001). This is being done as a predecessor towards general removal of MMX register usage. Since there is almost no usage of the 3DNow! intrinsics, and no modern hardware even implements them, simple removal seems like the best option. Thus we should avoid passing these to the backend, since otherwise we get a diagnostic about it: '-3dnow' is not a recognized feature for this target (ignoring feature) '-3dnowa' is not a recognized feature for this target (ignoring feature) We could try to disable them only up to LLVM 19 (not the C side one, but the one used by `rustc`, which may be built with a range of LLVMs). However, to avoid more complexity, we can likely just remove them altogether. According to Nikita [2]: > I don't think it's needed because LLVM should not generate 3dnow > instructions unless specifically asked to, using intrinsics that > Rust does not provide in the first place. Thus do so, like Rust did for one of their builtin targets [3]. For those curious: Clang will warn only about trying to enable them (`-m3dnow{,a}`), but not about disabling them (`-mno-3dnow{,a}`), so there is no change needed there. Cc: Nikita Popov <github@npopov.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: x86@kernel.org Link: https://github.com/llvm/llvm-project/commit/f0eb5587ceeb641445b64cb264c822b4751de04a [1] Link: https://github.com/rust-lang/rust/pull/127864#issuecomment-2235898760 [2] Link: https://github.com/rust-lang/rust/pull/127864 [3] Closes: https://github.com/Rust-for-Linux/linux/issues/1094 Tested-by: Benno Lossin <benno.lossin@proton.me> Tested-by: Alice Ryhl <aliceryhl@google.com> Link: https://lore.kernel.org/r/20240806144558.114461-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-08-06 07:45:58 -07:00
let mut features = "-mmx,+soft-float".to_string();
if cfg.has("MITIGATION_RETPOLINE") {
x86/rust: support MITIGATION_RETPOLINE Support `MITIGATION_RETPOLINE` by enabling the target features that Clang does. The existing target feature being enabled was a leftover from our old `rust` branch, and it is not enough: the target feature `retpoline-external-thunk` only implies `retpoline-indirect-calls`, but not `retpoline-indirect-branches` (see LLVM's `X86.td`), unlike Clang's flag of the same name `-mretpoline-external-thunk` which does imply both (see Clang's `lib/Driver/ToolChains/Arch/X86.cpp`). Without this, `objtool` would complain if enabled for Rust, e.g.: rust/core.o: warning: objtool: _R...escape_default+0x13: indirect jump found in RETPOLINE build In addition, change the comment to note that LLVM is the one disabling jump tables when retpoline is enabled, thus we do not need to use `-Zno-jump-tables` for Rust here -- see commit c58f2166ab39 ("Introduce the "retpoline" x86 mitigation technique ...") [1]: The goal is simple: avoid generating code which contains an indirect branch that could have its prediction poisoned by an attacker. In many cases, the compiler can simply use directed conditional branches and a small search tree. LLVM already has support for lowering switches in this way and the first step of this patch is to disable jump-table lowering of switches and introduce a pass to rewrite explicit indirectbr sequences into a switch over integers. As well as a live example at [2]. These should be eventually enabled via `-Ctarget-feature` when `rustc` starts recognizing them (or via a new dedicated flag) [3]. Cc: Daniel Borkmann <daniel@iogearbox.net> Link: https://github.com/llvm/llvm-project/commit/c58f2166ab3987f37cb0d7815b561bff5a20a69a [1] Link: https://godbolt.org/z/G4YPr58qG [2] Link: https://github.com/rust-lang/rust/issues/116852 [3] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Link: https://github.com/Rust-for-Linux/linux/issues/945 Link: https://lore.kernel.org/r/20240725183325.122827-3-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-07-25 11:33:19 -07:00
// 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";
x86/rust: support MITIGATION_RETPOLINE Support `MITIGATION_RETPOLINE` by enabling the target features that Clang does. The existing target feature being enabled was a leftover from our old `rust` branch, and it is not enough: the target feature `retpoline-external-thunk` only implies `retpoline-indirect-calls`, but not `retpoline-indirect-branches` (see LLVM's `X86.td`), unlike Clang's flag of the same name `-mretpoline-external-thunk` which does imply both (see Clang's `lib/Driver/ToolChains/Arch/X86.cpp`). Without this, `objtool` would complain if enabled for Rust, e.g.: rust/core.o: warning: objtool: _R...escape_default+0x13: indirect jump found in RETPOLINE build In addition, change the comment to note that LLVM is the one disabling jump tables when retpoline is enabled, thus we do not need to use `-Zno-jump-tables` for Rust here -- see commit c58f2166ab39 ("Introduce the "retpoline" x86 mitigation technique ...") [1]: The goal is simple: avoid generating code which contains an indirect branch that could have its prediction poisoned by an attacker. In many cases, the compiler can simply use directed conditional branches and a small search tree. LLVM already has support for lowering switches in this way and the first step of this patch is to disable jump-table lowering of switches and introduce a pass to rewrite explicit indirectbr sequences into a switch over integers. As well as a live example at [2]. These should be eventually enabled via `-Ctarget-feature` when `rustc` starts recognizing them (or via a new dedicated flag) [3]. Cc: Daniel Borkmann <daniel@iogearbox.net> Link: https://github.com/llvm/llvm-project/commit/c58f2166ab3987f37cb0d7815b561bff5a20a69a [1] Link: https://godbolt.org/z/G4YPr58qG [2] Link: https://github.com/rust-lang/rust/issues/116852 [3] Reviewed-by: Gary Guo <gary@garyguo.net> Tested-by: Alice Ryhl <aliceryhl@google.com> Tested-by: Benno Lossin <benno.lossin@proton.me> Link: https://github.com/Rust-for-Linux/linux/issues/945 Link: https://lore.kernel.org/r/20240725183325.122827-3-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-07-25 11:33:19 -07:00
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",
);
rust: x86: remove `-3dnow{,a}` from target features LLVM 19 is dropping support for 3DNow! in commit f0eb5587ceeb ("Remove support for 3DNow!, both intrinsics and builtins. (#96246)"): Remove support for 3DNow!, both intrinsics and builtins. (#96246) This set of instructions was only supported by AMD chips starting in the K6-2 (introduced 1998), and before the "Bulldozer" family (2011). They were never much used, as they were effectively superseded by the more-widely-implemented SSE (first implemented on the AMD side in Athlon XP in 2001). This is being done as a predecessor towards general removal of MMX register usage. Since there is almost no usage of the 3DNow! intrinsics, and no modern hardware even implements them, simple removal seems like the best option. Thus we should avoid passing these to the backend, since otherwise we get a diagnostic about it: '-3dnow' is not a recognized feature for this target (ignoring feature) '-3dnowa' is not a recognized feature for this target (ignoring feature) We could try to disable them only up to LLVM 19 (not the C side one, but the one used by `rustc`, which may be built with a range of LLVMs). However, to avoid more complexity, we can likely just remove them altogether. According to Nikita [2]: > I don't think it's needed because LLVM should not generate 3dnow > instructions unless specifically asked to, using intrinsics that > Rust does not provide in the first place. Thus do so, like Rust did for one of their builtin targets [3]. For those curious: Clang will warn only about trying to enable them (`-m3dnow{,a}`), but not about disabling them (`-mno-3dnow{,a}`), so there is no change needed there. Cc: Nikita Popov <github@npopov.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: x86@kernel.org Link: https://github.com/llvm/llvm-project/commit/f0eb5587ceeb641445b64cb264c822b4751de04a [1] Link: https://github.com/rust-lang/rust/pull/127864#issuecomment-2235898760 [2] Link: https://github.com/rust-lang/rust/pull/127864 [3] Closes: https://github.com/Rust-for-Linux/linux/issues/1094 Tested-by: Benno Lossin <benno.lossin@proton.me> Tested-by: Alice Ryhl <aliceryhl@google.com> Link: https://lore.kernel.org/r/20240806144558.114461-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
2024-08-06 07:45:58 -07:00
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);
}