61dc38c065
Currently, we have partial Spectre mitigation: we protect heap accesses with dynamic bounds checks. Specifically, we guard against errant accesses on the misspeculated path beyond the bounds-check conditional branch by adding a conditional move that is also dependent on the bounds-check condition. This data dependency on the condition is not speculated and thus will always pick the "safe" value (in the heap case, a NULL address) on the misspeculated path, until the pipeline flushes and recovers onto the correct path. This PR uses the same technique both for table accesses -- used to implement Wasm tables -- and for jumptables, used to implement Wasm `br_table` instructions. In the case of Wasm tables, the cmove picks the table base address on the misspeculated path. This is equivalent to reading the first table entry. This prevents loads of arbitrary data addresses on the misspeculated path. In the case of `br_table`, the cmove picks index 0 on the misspeculated path. This is safer than allowing a branch to an address loaded from an index under misspeculation (i.e., it preserves control-flow integrity even under misspeculation). The table mitigation is controlled by a Cranelift setting, on by default. The br_table mitigation is always on, because it is part of the single lowering pseudoinstruction. In both cases, the impact should be minimal: a single extra cmove in a (relatively) rarely-used operation. The table mitigation is architecture-independent (happens during legalization); the br_table mitigation has been implemented for both x64 and aarch64. (I don't know enough about s390x to implement this confidently there, but would happily review a PR to do the same on that platform.)
583 lines
18 KiB
Rust
583 lines
18 KiB
Rust
//! Shared settings module.
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//!
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//! This module defines data structures to access the settings defined in the meta language.
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//!
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//! Each settings group is translated to a `Flags` struct either in this module or in its
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//! ISA-specific `settings` module. The struct provides individual getter methods for all of the
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//! settings as well as computed predicate flags.
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//!
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//! The `Flags` struct is immutable once it has been created. A `Builder` instance is used to
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//! create it.
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//!
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//! # Example
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//! ```
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//! use cranelift_codegen::settings::{self, Configurable};
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//!
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//! let mut b = settings::builder();
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//! b.set("opt_level", "speed_and_size");
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//!
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//! let f = settings::Flags::new(b);
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//! assert_eq!(f.opt_level(), settings::OptLevel::SpeedAndSize);
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//! ```
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use crate::constant_hash::{probe, simple_hash};
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use crate::isa::TargetIsa;
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use alloc::boxed::Box;
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use alloc::string::{String, ToString};
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use core::fmt;
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use core::str;
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/// A string-based configurator for settings groups.
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///
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/// The `Configurable` protocol allows settings to be modified by name before a finished `Flags`
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/// struct is created.
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pub trait Configurable {
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/// Set the string value of any setting by name.
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///
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/// This can set any type of setting whether it is numeric, boolean, or enumerated.
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fn set(&mut self, name: &str, value: &str) -> SetResult<()>;
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/// Enable a boolean setting or apply a preset.
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///
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/// If the identified setting isn't a boolean or a preset, a `BadType` error is returned.
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fn enable(&mut self, name: &str) -> SetResult<()>;
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}
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/// Represents the kind of setting.
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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pub enum SettingKind {
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/// The setting is an enumeration.
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Enum,
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/// The setting is a number.
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Num,
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/// The setting is a boolean.
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Bool,
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/// The setting is a preset.
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Preset,
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}
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/// Represents an available builder setting.
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///
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/// This is used for iterating settings in a builder.
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#[derive(Clone, Copy, Debug)]
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pub struct Setting {
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/// The name of the setting.
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pub name: &'static str,
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/// The description of the setting.
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pub description: &'static str,
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/// The kind of the setting.
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pub kind: SettingKind,
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/// The supported values of the setting (for enum values).
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pub values: Option<&'static [&'static str]>,
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}
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/// Represents a setting value.
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///
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/// This is used for iterating values in `Flags`.
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pub struct Value {
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/// The name of the setting associated with this value.
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pub name: &'static str,
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pub(crate) detail: detail::Detail,
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pub(crate) values: Option<&'static [&'static str]>,
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pub(crate) value: u8,
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}
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impl Value {
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/// Gets the kind of setting.
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pub fn kind(&self) -> SettingKind {
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match &self.detail {
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detail::Detail::Enum { .. } => SettingKind::Enum,
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detail::Detail::Num => SettingKind::Num,
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detail::Detail::Bool { .. } => SettingKind::Bool,
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detail::Detail::Preset => unreachable!(),
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}
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}
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/// Gets the enum value if the value is from an enum setting.
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pub fn as_enum(&self) -> Option<&'static str> {
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self.values.map(|v| v[self.value as usize])
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}
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/// Gets the numerical value if the value is from a num setting.
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pub fn as_num(&self) -> Option<u8> {
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match &self.detail {
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detail::Detail::Num => Some(self.value),
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_ => None,
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}
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}
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/// Gets the boolean value if the value is from a boolean setting.
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pub fn as_bool(&self) -> Option<bool> {
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match &self.detail {
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detail::Detail::Bool { bit } => Some(self.value & (1 << bit) != 0),
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_ => None,
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}
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}
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}
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impl fmt::Display for Value {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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if let Some(enum_variant) = self.as_enum() {
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write!(f, "{}={}", self.name, enum_variant)
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} else if let Some(num) = self.as_num() {
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write!(f, "{}={}", self.name, num)
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} else if let Some(b) = self.as_bool() {
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if b {
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write!(f, "{}=1", self.name)
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} else {
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write!(f, "{}=0", self.name)
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}
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} else {
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unreachable!()
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}
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}
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}
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/// Collect settings values based on a template.
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#[derive(Clone, Hash)]
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pub struct Builder {
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template: &'static detail::Template,
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bytes: Box<[u8]>,
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}
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impl Builder {
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/// Create a new builder with defaults and names from the given template.
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pub fn new(tmpl: &'static detail::Template) -> Self {
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Self {
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template: tmpl,
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bytes: tmpl.defaults.into(),
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}
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}
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/// Extract contents of builder once everything is configured.
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pub fn state_for(self, name: &str) -> Box<[u8]> {
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assert_eq!(name, self.template.name);
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self.bytes
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}
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/// Iterates the available settings in the builder.
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pub fn iter(&self) -> impl Iterator<Item = Setting> {
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let template = self.template;
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template.descriptors.iter().map(move |d| {
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let (kind, values) = match d.detail {
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detail::Detail::Enum { last, enumerators } => {
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let values = template.enums(last, enumerators);
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(SettingKind::Enum, Some(values))
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}
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detail::Detail::Num => (SettingKind::Num, None),
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detail::Detail::Bool { .. } => (SettingKind::Bool, None),
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detail::Detail::Preset => (SettingKind::Preset, None),
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};
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Setting {
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name: d.name,
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description: d.description,
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kind,
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values,
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}
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})
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}
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/// Set the value of a single bit.
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fn set_bit(&mut self, offset: usize, bit: u8, value: bool) {
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let byte = &mut self.bytes[offset];
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let mask = 1 << bit;
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if value {
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*byte |= mask;
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} else {
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*byte &= !mask;
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}
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}
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/// Apply a preset. The argument is a slice of (mask, value) bytes.
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fn apply_preset(&mut self, values: &[(u8, u8)]) {
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for (byte, &(mask, value)) in self.bytes.iter_mut().zip(values) {
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*byte = (*byte & !mask) | value;
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}
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}
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/// Look up a descriptor by name.
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fn lookup(&self, name: &str) -> SetResult<(usize, detail::Detail)> {
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match probe(self.template, name, simple_hash(name)) {
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Err(_) => Err(SetError::BadName(name.to_string())),
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Ok(entry) => {
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let d = &self.template.descriptors[self.template.hash_table[entry] as usize];
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Ok((d.offset as usize, d.detail))
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}
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}
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}
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}
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fn parse_bool_value(value: &str) -> SetResult<bool> {
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match value {
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"true" | "on" | "yes" | "1" => Ok(true),
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"false" | "off" | "no" | "0" => Ok(false),
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_ => Err(SetError::BadValue("bool".to_string())),
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}
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}
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fn parse_enum_value(value: &str, choices: &[&str]) -> SetResult<u8> {
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match choices.iter().position(|&tag| tag == value) {
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Some(idx) => Ok(idx as u8),
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None => {
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// TODO: Use `join` instead of this code, once
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// https://github.com/rust-lang/rust/issues/27747 is resolved.
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let mut all_choices = String::new();
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let mut first = true;
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for choice in choices {
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if first {
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first = false
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} else {
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all_choices += ", ";
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}
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all_choices += choice;
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}
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Err(SetError::BadValue(format!("any among {}", all_choices)))
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}
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}
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}
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impl Configurable for Builder {
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fn enable(&mut self, name: &str) -> SetResult<()> {
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use self::detail::Detail;
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let (offset, detail) = self.lookup(name)?;
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match detail {
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Detail::Bool { bit } => {
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self.set_bit(offset, bit, true);
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Ok(())
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}
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Detail::Preset => {
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self.apply_preset(&self.template.presets[offset..]);
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Ok(())
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}
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_ => Err(SetError::BadType),
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}
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}
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fn set(&mut self, name: &str, value: &str) -> SetResult<()> {
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use self::detail::Detail;
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let (offset, detail) = self.lookup(name)?;
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match detail {
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Detail::Bool { bit } => {
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self.set_bit(offset, bit, parse_bool_value(value)?);
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}
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Detail::Num => {
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self.bytes[offset] = value
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.parse()
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.map_err(|_| SetError::BadValue("number".to_string()))?;
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}
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Detail::Enum { last, enumerators } => {
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self.bytes[offset] =
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parse_enum_value(value, self.template.enums(last, enumerators))?;
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}
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Detail::Preset => return Err(SetError::BadName(name.to_string())),
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}
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Ok(())
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}
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}
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/// An error produced when changing a setting.
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#[derive(Debug, PartialEq, Eq)]
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pub enum SetError {
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/// No setting by this name exists.
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BadName(String),
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/// Type mismatch for setting (e.g., setting an enum setting as a bool).
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BadType,
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/// This is not a valid value for this setting.
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BadValue(String),
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}
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impl std::error::Error for SetError {}
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impl fmt::Display for SetError {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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match self {
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SetError::BadName(name) => write!(f, "No existing setting named '{}'", name),
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SetError::BadType => {
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write!(f, "Trying to set a setting with the wrong type")
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}
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SetError::BadValue(value) => {
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write!(f, "Unexpected value for a setting, expected {}", value)
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}
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}
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}
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}
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/// A result returned when changing a setting.
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pub type SetResult<T> = Result<T, SetError>;
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/// A reference to just the boolean predicates of a settings object.
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///
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/// The settings objects themselves are generated and appear in the `isa/*/settings.rs` modules.
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/// Each settings object provides a `predicate_view()` method that makes it possible to query
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/// ISA predicates by number.
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#[derive(Clone, Copy, Hash)]
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pub struct PredicateView<'a>(&'a [u8]);
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impl<'a> PredicateView<'a> {
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/// Create a new view of a precomputed predicate vector.
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///
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/// See the `predicate_view()` method on the various `Flags` types defined for each ISA.
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pub fn new(bits: &'a [u8]) -> Self {
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PredicateView(bits)
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}
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/// Check a numbered predicate.
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pub fn test(self, p: usize) -> bool {
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self.0[p / 8] & (1 << (p % 8)) != 0
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}
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}
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/// Implementation details for generated code.
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///
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/// This module holds definitions that need to be public so the can be instantiated by generated
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/// code in other modules.
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pub mod detail {
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use crate::constant_hash;
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use core::fmt;
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use core::hash::Hash;
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/// An instruction group template.
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#[derive(Hash)]
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pub struct Template {
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/// Name of the instruction group.
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pub name: &'static str,
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/// List of setting descriptors.
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pub descriptors: &'static [Descriptor],
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/// Union of all enumerators.
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pub enumerators: &'static [&'static str],
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/// Hash table of settings.
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pub hash_table: &'static [u16],
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/// Default values.
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pub defaults: &'static [u8],
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/// Pairs of (mask, value) for presets.
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pub presets: &'static [(u8, u8)],
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}
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impl Template {
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/// Get enumerators corresponding to a `Details::Enum`.
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pub fn enums(&self, last: u8, enumerators: u16) -> &[&'static str] {
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let from = enumerators as usize;
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let len = usize::from(last) + 1;
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&self.enumerators[from..from + len]
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}
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/// Format a setting value as a TOML string. This is mostly for use by the generated
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/// `Display` implementation.
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pub fn format_toml_value(
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&self,
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detail: Detail,
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byte: u8,
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f: &mut fmt::Formatter,
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) -> fmt::Result {
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match detail {
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Detail::Bool { bit } => write!(f, "{}", (byte & (1 << bit)) != 0),
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Detail::Num => write!(f, "{}", byte),
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Detail::Enum { last, enumerators } => {
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if byte <= last {
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let tags = self.enums(last, enumerators);
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write!(f, "\"{}\"", tags[usize::from(byte)])
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} else {
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write!(f, "{}", byte)
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}
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}
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// Presets aren't printed. They are reflected in the other settings.
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Detail::Preset { .. } => Ok(()),
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}
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}
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}
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/// The template contains a hash table for by-name lookup.
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impl<'a> constant_hash::Table<&'a str> for Template {
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fn len(&self) -> usize {
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self.hash_table.len()
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}
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fn key(&self, idx: usize) -> Option<&'a str> {
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let e = self.hash_table[idx] as usize;
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if e < self.descriptors.len() {
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Some(self.descriptors[e].name)
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} else {
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None
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}
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}
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}
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/// A setting descriptor holds the information needed to generically set and print a setting.
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///
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/// Each settings group will be represented as a constant DESCRIPTORS array.
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#[derive(Hash)]
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pub struct Descriptor {
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/// Lower snake-case name of setting as defined in meta.
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pub name: &'static str,
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/// The description of the setting.
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pub description: &'static str,
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/// Offset of byte containing this setting.
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pub offset: u32,
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/// Additional details, depending on the kind of setting.
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pub detail: Detail,
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}
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/// The different kind of settings along with descriptor bits that depend on the kind.
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#[derive(Clone, Copy, Hash)]
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pub enum Detail {
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/// A boolean setting only uses one bit, numbered from LSB.
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Bool {
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/// 0-7.
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bit: u8,
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},
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/// A numerical setting uses the whole byte.
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Num,
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/// An Enum setting uses a range of enumerators.
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Enum {
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/// Numerical value of last enumerator, allowing for 1-256 enumerators.
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last: u8,
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/// First enumerator in the ENUMERATORS table.
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enumerators: u16,
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},
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/// A preset is not an individual setting, it is a collection of settings applied at once.
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///
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/// The `Descriptor::offset` field refers to the `PRESETS` table.
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Preset,
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}
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impl Detail {
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/// Check if a detail is a Detail::Preset. Useful because the Descriptor
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/// offset field has a different meaning when the detail is a preset.
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pub fn is_preset(self) -> bool {
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match self {
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Self::Preset => true,
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_ => false,
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}
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}
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}
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}
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|
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// Include code generated by `meta/gen_settings.rs`. This file contains a public `Flags` struct
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// with an implementation for all of the settings defined in
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// `cranelift-codegen/meta/src/shared/settings.rs`.
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include!(concat!(env!("OUT_DIR"), "/settings.rs"));
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|
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/// Wrapper containing flags and optionally a `TargetIsa` trait object.
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///
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/// A few passes need to access the flags but only optionally a target ISA. The `FlagsOrIsa`
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/// wrapper can be used to pass either, and extract the flags so they are always accessible.
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#[derive(Clone, Copy)]
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pub struct FlagsOrIsa<'a> {
|
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/// Flags are always present.
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pub flags: &'a Flags,
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|
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/// The ISA may not be present.
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pub isa: Option<&'a dyn TargetIsa>,
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}
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|
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impl<'a> From<&'a Flags> for FlagsOrIsa<'a> {
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fn from(flags: &'a Flags) -> FlagsOrIsa {
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FlagsOrIsa { flags, isa: None }
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}
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}
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|
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impl<'a> From<&'a dyn TargetIsa> for FlagsOrIsa<'a> {
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fn from(isa: &'a dyn TargetIsa) -> FlagsOrIsa {
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FlagsOrIsa {
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flags: isa.flags(),
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isa: Some(isa),
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}
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}
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}
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|
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#[cfg(test)]
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mod tests {
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use super::Configurable;
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use super::SetError::*;
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use super::{builder, Flags};
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use alloc::string::ToString;
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|
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#[test]
|
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fn display_default() {
|
|
let b = builder();
|
|
let f = Flags::new(b);
|
|
assert_eq!(
|
|
f.to_string(),
|
|
r#"[shared]
|
|
opt_level = "none"
|
|
tls_model = "none"
|
|
libcall_call_conv = "isa_default"
|
|
baldrdash_prologue_words = 0
|
|
probestack_size_log2 = 12
|
|
regalloc_checker = false
|
|
enable_verifier = true
|
|
is_pic = false
|
|
use_colocated_libcalls = false
|
|
avoid_div_traps = false
|
|
enable_float = true
|
|
enable_nan_canonicalization = false
|
|
enable_pinned_reg = false
|
|
use_pinned_reg_as_heap_base = false
|
|
enable_simd = false
|
|
enable_atomics = true
|
|
enable_safepoints = false
|
|
enable_llvm_abi_extensions = false
|
|
unwind_info = true
|
|
machine_code_cfg_info = false
|
|
emit_all_ones_funcaddrs = false
|
|
enable_probestack = true
|
|
probestack_func_adjusts_sp = false
|
|
enable_jump_tables = true
|
|
enable_heap_access_spectre_mitigation = true
|
|
enable_table_access_spectre_mitigation = true
|
|
"#
|
|
);
|
|
assert_eq!(f.opt_level(), super::OptLevel::None);
|
|
assert_eq!(f.enable_simd(), false);
|
|
assert_eq!(f.baldrdash_prologue_words(), 0);
|
|
}
|
|
|
|
#[test]
|
|
fn modify_bool() {
|
|
let mut b = builder();
|
|
assert_eq!(b.enable("not_there"), Err(BadName("not_there".to_string())));
|
|
assert_eq!(b.enable("enable_simd"), Ok(()));
|
|
assert_eq!(b.set("enable_simd", "false"), Ok(()));
|
|
|
|
let f = Flags::new(b);
|
|
assert_eq!(f.enable_simd(), false);
|
|
}
|
|
|
|
#[test]
|
|
fn modify_string() {
|
|
let mut b = builder();
|
|
assert_eq!(
|
|
b.set("not_there", "true"),
|
|
Err(BadName("not_there".to_string()))
|
|
);
|
|
assert_eq!(b.set("enable_simd", ""), Err(BadValue("bool".to_string())));
|
|
assert_eq!(
|
|
b.set("enable_simd", "best"),
|
|
Err(BadValue("bool".to_string()))
|
|
);
|
|
assert_eq!(
|
|
b.set("opt_level", "true"),
|
|
Err(BadValue(
|
|
"any among none, speed, speed_and_size".to_string()
|
|
))
|
|
);
|
|
assert_eq!(b.set("opt_level", "speed"), Ok(()));
|
|
assert_eq!(b.set("enable_simd", "0"), Ok(()));
|
|
|
|
let f = Flags::new(b);
|
|
assert_eq!(f.enable_simd(), false);
|
|
assert_eq!(f.opt_level(), super::OptLevel::Speed);
|
|
}
|
|
}
|