Ensure miri only uses fallback bodies that have manually been vetted to preserve all UB that the native intrinsic would have

This commit is contained in:
Oli Scherer 2024-04-23 13:32:30 +00:00
parent 351658ae66
commit 821d23b329
8 changed files with 44 additions and 2 deletions

View File

@ -468,7 +468,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
// CTFE-specific intrinsics.
let Some(ret) = target else {
// Handle diverging intrinsics.
// Handle diverging intrinsics. We can't handle any of them (that are not already
// handled above), but check if there is a fallback body.
if ecx.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
throw_unsup_format!(
"intrinsic `{intrinsic_name}` is not supported at compile-time"

View File

@ -141,7 +141,7 @@ pub(crate) fn registered_tools(tcx: TyCtxt<'_>, (): ()) -> RegisteredTools {
}
// We implicitly add `rustfmt`, `clippy`, `diagnostic` to known tools,
// but it's not an error to register them explicitly.
let predefined_tools = [sym::clippy, sym::rustfmt, sym::diagnostic];
let predefined_tools = [sym::clippy, sym::rustfmt, sym::diagnostic, sym::miri];
registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
registered_tools
}

View File

@ -987,6 +987,7 @@ pub const unsafe fn assume(b: bool) {
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_nounwind]
#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
pub const fn likely(b: bool) -> bool {
b
}
@ -1006,6 +1007,7 @@ pub const fn likely(b: bool) -> bool {
#[unstable(feature = "core_intrinsics", issue = "none")]
#[rustc_intrinsic]
#[rustc_nounwind]
#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
pub const fn unlikely(b: bool) -> bool {
b
}
@ -2526,6 +2528,7 @@ extern "rust-intrinsic" {
#[rustc_nounwind]
#[rustc_do_not_const_check]
#[inline]
#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
(ptr == other) as u8
}

View File

@ -14,6 +14,7 @@ pub enum AtomicOp {
impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
/// Calls the atomic intrinsic `intrinsic`; the `atomic_` prefix has already been removed.
/// Returns `Ok(true)` if the intrinsic was handled.
fn emulate_atomic_intrinsic(
&mut self,
intrinsic_name: &str,

View File

@ -11,6 +11,7 @@ use rustc_middle::{
ty::{self, FloatTy},
};
use rustc_target::abi::Size;
use rustc_span::{sym, Symbol};
use crate::*;
use atomic::EvalContextExt as _;
@ -48,6 +49,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
// All remaining supported intrinsics have a return place.
let ret = match ret {
// FIXME: add fallback body support once we actually have a diverging intrinsic with a fallback body
None => throw_unsup_format!("unimplemented (diverging) intrinsic: `{intrinsic_name}`"),
Some(p) => p,
};
@ -63,9 +65,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
// The rest jumps to `ret` immediately.
if !this.emulate_intrinsic_by_name(intrinsic_name, instance.args, args, dest)? {
// We haven't handled the intrinsic, let's see if we can use a fallback body.
if this.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
throw_unsup_format!("unimplemented intrinsic: `{intrinsic_name}`")
}
let intrinsic_fallback_checks_ub = Symbol::intern("intrinsic_fallback_checks_ub");
if this.tcx.get_attrs_by_path(instance.def_id(), &[sym::miri, intrinsic_fallback_checks_ub]).next().is_none() {
throw_unsup_format!("miri can only use intrinsic fallback bodies that check UB. After verifying that `{intrinsic_name}` does so, add the `#[miri::intrinsic_fallback_checks_ub]` attribute to it; also ping @rust-lang/miri when you do that");
}
return Ok(Some(ty::Instance {
def: ty::InstanceDef::Item(instance.def_id()),
args: instance.args,
@ -78,6 +85,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
}
/// Emulates a Miri-supported intrinsic (not supported by the core engine).
/// Returns `Ok(true)` if the intrinsic was handled.
fn emulate_intrinsic_by_name(
&mut self,
intrinsic_name: &str,

View File

@ -16,6 +16,7 @@ pub(crate) enum MinMax {
impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
/// Calls the simd intrinsic `intrinsic`; the `simd_` prefix has already been removed.
/// Returns `Ok(true)` if the intrinsic was handled.
fn emulate_simd_intrinsic(
&mut self,
intrinsic_name: &str,

View File

@ -0,0 +1,14 @@
#![feature(rustc_attrs, effects)]
#[rustc_intrinsic]
#[rustc_nounwind]
#[rustc_do_not_const_check]
#[inline]
pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
(ptr == other) as u8
}
fn main() {
ptr_guaranteed_cmp::<()>(std::ptr::null(), std::ptr::null());
//~^ ERROR: can only use intrinsic fallback bodies that check UB.
}

View File

@ -0,0 +1,14 @@
error: unsupported operation: miri can only use intrinsic fallback bodies that check UB. After verifying that `ptr_guaranteed_cmp` does so, add the `#[miri::intrinsic_fallback_checks_ub]` attribute to it; also ping @rust-lang/miri when you do that
--> $DIR/intrinsic_fallback_checks_ub.rs:LL:CC
|
LL | ptr_guaranteed_cmp::<()>(std::ptr::null(), std::ptr::null());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ miri can only use intrinsic fallback bodies that check UB. After verifying that `ptr_guaranteed_cmp` does so, add the `#[miri::intrinsic_fallback_checks_ub]` attribute to it; also ping @rust-lang/miri when you do that
|
= help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
= note: BACKTRACE:
= note: inside `main` at $DIR/intrinsic_fallback_checks_ub.rs:LL:CC
note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
error: aborting due to 1 previous error