Auto merge of rust-lang#74775 - RalfJung:miri-alloc-ids, r=oli-obk

 Miri: replace canonical_alloc_id mechanism by extern_static_alloc_id

We only have to call `extern_static_alloc_id` when a `Pointer` is "imported" from the `tcx` to the machine, not on each access. Also drop the old hook for TLS handling, it is not needed any more.

The Miri side of this is at rust-lang/miri#1489.

Fixes rust-lang#71194
r? @oli-obk

Author: bors

src/librustc_middle/mir/interpret/error.rs

@@ -502,8 +502,6 @@ impl fmt::Display for UndefinedBehaviorInfo<'_> {
 pub enum UnsupportedOpInfo {
     /// Free-form case. Only for errors that are never caught!
     Unsupported(String),
-    /// Accessing an unsupported foreign static.
-    ReadForeignStatic(DefId),
     /// Could not find MIR for a function.
     NoMirFor(DefId),
     /// Encountered a pointer where we needed raw bytes.
@@ -515,16 +513,16 @@ pub enum UnsupportedOpInfo {
     ReadBytesAsPointer,
     /// Accessing thread local statics
     ThreadLocalStatic(DefId),
+    /// Accessing an unsupported extern static.
+    ReadExternStatic(DefId),
 }
 
 impl fmt::Display for UnsupportedOpInfo {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use UnsupportedOpInfo::*;
         match self {
             Unsupported(ref msg) => write!(f, "{}", msg),
-            ReadForeignStatic(did) => {
-                write!(f, "cannot read from foreign (extern) static ({:?})", did)
-            }
+            ReadExternStatic(did) => write!(f, "cannot read from extern static ({:?})", did),
             NoMirFor(did) => write!(f, "no MIR body is available for {:?}", did),
             ReadPointerAsBytes => write!(f, "unable to turn pointer into raw bytes",),
             ReadBytesAsPointer => write!(f, "unable to turn bytes into a pointer"),

src/librustc_mir/const_eval/mod.rs

@@ -41,7 +41,7 @@ pub(crate) fn destructure_const<'tcx>(
 ) -> mir::DestructuredConst<'tcx> {
     trace!("destructure_const: {:?}", val);
     let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
-    let op = ecx.eval_const_to_op(val, None).unwrap();
+    let op = ecx.const_to_op(val, None).unwrap();
 
     // We go to `usize` as we cannot allocate anything bigger anyway.
     let (field_count, variant, down) = match val.ty.kind {

src/librustc_mir/interpret/eval_context.rs

@@ -323,14 +323,17 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     /// Call this to turn untagged "global" pointers (obtained via `tcx`) into
-    /// the *canonical* machine pointer to the allocation.  Must never be used
-    /// for any other pointers!
+    /// the machine pointer to the allocation.  Must never be used
+    /// for any other pointers, nor for TLS statics.
     ///
-    /// This represents a *direct* access to that memory, as opposed to access
-    /// through a pointer that was created by the program.
+    /// Using the resulting pointer represents a *direct* access to that memory
+    /// (e.g. by directly using a `static`),
+    /// as opposed to access through a pointer that was created by the program.
+    ///
+    /// This function can fail only if `ptr` points to an `extern static`.
     #[inline(always)]
-    pub fn tag_global_base_pointer(&self, ptr: Pointer) -> Pointer<M::PointerTag> {
-        self.memory.tag_global_base_pointer(ptr)
+    pub fn global_base_pointer(&self, ptr: Pointer) -> InterpResult<'tcx, Pointer<M::PointerTag>> {
+        self.memory.global_base_pointer(ptr)
     }
 
     #[inline(always)]
@@ -845,12 +848,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         };
         let val = self.tcx.const_eval_global_id(param_env, gid, Some(self.tcx.span))?;
 
-        // Even though `ecx.const_eval` is called from `eval_const_to_op` we can never have a
+        // Even though `ecx.const_eval` is called from `const_to_op` we can never have a
         // recursion deeper than one level, because the `tcx.const_eval` above is guaranteed to not
-        // return `ConstValue::Unevaluated`, which is the only way that `eval_const_to_op` will call
+        // return `ConstValue::Unevaluated`, which is the only way that `const_to_op` will call
         // `ecx.const_eval`.
         let const_ = ty::Const { val: ty::ConstKind::Value(val), ty };
-        self.eval_const_to_op(&const_, None)
+        self.const_to_op(&const_, None)
     }
 
     pub fn const_eval_raw(

src/librustc_mir/interpret/machine.rs

@@ -238,45 +238,30 @@ pub trait Machine<'mir, 'tcx>: Sized {
         Ok(())
     }
 
-    /// Called for *every* memory access to determine the real ID of the given allocation.
-    /// This provides a way for the machine to "redirect" certain allocations as it sees fit.
-    ///
-    /// This is used by Miri to redirect extern statics to real allocations.
-    ///
-    /// This function must be idempotent.
-    #[inline]
-    fn canonical_alloc_id(_mem: &Memory<'mir, 'tcx, Self>, id: AllocId) -> AllocId {
-        id
+    /// Return the `AllocId` for the given thread-local static in the current thread.
+    fn thread_local_static_alloc_id(
+        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        def_id: DefId,
+    ) -> InterpResult<'tcx, AllocId> {
+        throw_unsup!(ThreadLocalStatic(def_id))
     }
 
-    /// Called when converting a `ty::Const` to an operand (in
-    /// `eval_const_to_op`).
-    ///
-    /// Miri uses this callback for creating per thread allocations for thread
-    /// locals. In Rust, one way of creating a thread local is by marking a
-    /// static with `#[thread_local]`. On supported platforms this gets
-    /// translated to a LLVM thread local for which LLVM automatically ensures
-    /// that each thread gets its own copy. Since LLVM automatically handles
-    /// thread locals, the Rust compiler just treats thread local statics as
-    /// regular statics even though accessing a thread local static should be an
-    /// effectful computation that depends on the current thread. The long term
-    /// plan is to change MIR to make accesses to thread locals explicit
-    /// (https://github.com/rust-lang/rust/issues/70685). While the issue 70685
-    /// is not fixed, our current workaround in Miri is to use this function to
-    /// make per-thread copies of thread locals. Please note that we cannot make
-    /// these copies in `canonical_alloc_id` because that is too late: for
-    /// example, if one created a pointer in thread `t1` to a thread local and
-    /// sent it to another thread `t2`, resolving the access in
-    /// `canonical_alloc_id` would result in pointer pointing to `t2`'s thread
-    /// local and not `t1` as it should.
-    #[inline]
-    fn adjust_global_const(
-        _ecx: &InterpCx<'mir, 'tcx, Self>,
-        val: mir::interpret::ConstValue<'tcx>,
-    ) -> InterpResult<'tcx, mir::interpret::ConstValue<'tcx>> {
-        Ok(val)
+    /// Return the `AllocId` backing the given `extern static`.
+    fn extern_static_alloc_id(
+        mem: &Memory<'mir, 'tcx, Self>,
+        def_id: DefId,
+    ) -> InterpResult<'tcx, AllocId> {
+        // Use the `AllocId` associated with the `DefId`. Any actual *access* will fail.
+        Ok(mem.tcx.create_static_alloc(def_id))
     }
 
+    /// Return the "base" tag for the given *global* allocation: the one that is used for direct
+    /// accesses to this static/const/fn allocation. If `id` is not a global allocation,
+    /// this will return an unusable tag (i.e., accesses will be UB)!
+    ///
+    /// Called on the id returned by `thread_local_static_alloc_id` and `extern_static_alloc_id`, if needed.
+    fn tag_global_base_pointer(memory_extra: &Self::MemoryExtra, id: AllocId) -> Self::PointerTag;
+
     /// Called to initialize the "extra" state of an allocation and make the pointers
     /// it contains (in relocations) tagged.  The way we construct allocations is
     /// to always first construct it without extra and then add the extra.
@@ -309,13 +294,6 @@ pub trait Machine<'mir, 'tcx>: Sized {
         Ok(())
     }
 
-    /// Return the "base" tag for the given *global* allocation: the one that is used for direct
-    /// accesses to this static/const/fn allocation. If `id` is not a global allocation,
-    /// this will return an unusable tag (i.e., accesses will be UB)!
-    ///
-    /// Expects `id` to be already canonical, if needed.
-    fn tag_global_base_pointer(memory_extra: &Self::MemoryExtra, id: AllocId) -> Self::PointerTag;
-
     /// Executes a retagging operation
     #[inline]
     fn retag(
@@ -375,13 +353,6 @@ pub trait Machine<'mir, 'tcx>: Sized {
         _mem: &Memory<'mir, 'tcx, Self>,
         _ptr: Pointer<Self::PointerTag>,
     ) -> InterpResult<'tcx, u64>;
-
-    fn thread_local_alloc_id(
-        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        did: DefId,
-    ) -> InterpResult<'tcx, AllocId> {
-        throw_unsup!(ThreadLocalStatic(did))
-    }
 }
 
 // A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines

src/librustc_mir/interpret/memory.rs

@@ -14,6 +14,7 @@ use std::ptr;
 
 use rustc_ast::ast::Mutability;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, Instance, ParamEnv, TyCtxt};
 use rustc_target::abi::{Align, HasDataLayout, Size, TargetDataLayout};
 
@@ -118,6 +119,17 @@ pub struct Memory<'mir, 'tcx, M: Machine<'mir, 'tcx>> {
     pub tcx: TyCtxt<'tcx>,
 }
 
+/// Return the `tcx` allocation containing the initial value of the given static
+pub fn get_static(tcx: TyCtxt<'tcx>, def_id: DefId) -> InterpResult<'tcx, &'tcx Allocation> {
+    trace!("get_static: Need to compute {:?}", def_id);
+    let instance = Instance::mono(tcx, def_id);
+    let gid = GlobalId { instance, promoted: None };
+    // Use the raw query here to break validation cycles. Later uses of the static
+    // will call the full query anyway.
+    let raw_const = tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid))?;
+    Ok(tcx.global_alloc(raw_const.alloc_id).unwrap_memory())
+}
+
 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> HasDataLayout for Memory<'mir, 'tcx, M> {
     #[inline]
     fn data_layout(&self) -> &TargetDataLayout {
@@ -137,15 +149,36 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
     }
 
     /// Call this to turn untagged "global" pointers (obtained via `tcx`) into
-    /// the *canonical* machine pointer to the allocation.  Must never be used
-    /// for any other pointers!
+    /// the machine pointer to the allocation.  Must never be used
+    /// for any other pointers, nor for TLS statics.
+    ///
+    /// Using the resulting pointer represents a *direct* access to that memory
+    /// (e.g. by directly using a `static`),
+    /// as opposed to access through a pointer that was created by the program.
     ///
-    /// This represents a *direct* access to that memory, as opposed to access
-    /// through a pointer that was created by the program.
+    /// This function can fail only if `ptr` points to an `extern static`.
     #[inline]
-    pub fn tag_global_base_pointer(&self, ptr: Pointer) -> Pointer<M::PointerTag> {
-        let id = M::canonical_alloc_id(self, ptr.alloc_id);
-        ptr.with_tag(M::tag_global_base_pointer(&self.extra, id))
+    pub fn global_base_pointer(
+        &self,
+        mut ptr: Pointer,
+    ) -> InterpResult<'tcx, Pointer<M::PointerTag>> {
+        // We need to handle `extern static`.
+        let ptr = match self.tcx.get_global_alloc(ptr.alloc_id) {
+            Some(GlobalAlloc::Static(def_id)) if self.tcx.is_thread_local_static(def_id) => {
+                bug!("global memory cannot point to thread-local static")
+            }
+            Some(GlobalAlloc::Static(def_id)) if self.tcx.is_foreign_item(def_id) => {
+                ptr.alloc_id = M::extern_static_alloc_id(self, def_id)?;
+                ptr
+            }
+            _ => {
+                // No need to change the `AllocId`.
+                ptr
+            }
+        };
+        // And we need to get the tag.
+        let tag = M::tag_global_base_pointer(&self.extra, ptr.alloc_id);
+        Ok(ptr.with_tag(tag))
     }
 
     pub fn create_fn_alloc(
@@ -162,7 +195,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                 id
             }
         };
-        self.tag_global_base_pointer(Pointer::from(id))
+        // Functions are global allocations, so make sure we get the right base pointer.
+        // We know this is not an `extern static` so this cannot fail.
+        self.global_base_pointer(Pointer::from(id)).unwrap()
     }
 
     pub fn allocate(
@@ -195,6 +230,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             M::GLOBAL_KIND.map(MemoryKind::Machine),
             "dynamically allocating global memory"
         );
+        // This is a new allocation, not a new global one, so no `global_base_ptr`.
         let (alloc, tag) = M::init_allocation_extra(&self.extra, id, Cow::Owned(alloc), Some(kind));
         self.alloc_map.insert(id, (kind, alloc.into_owned()));
         Pointer::from(id).with_tag(tag)
@@ -437,6 +473,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             Some(GlobalAlloc::Function(..)) => throw_ub!(DerefFunctionPointer(id)),
             None => throw_ub!(PointerUseAfterFree(id)),
             Some(GlobalAlloc::Static(def_id)) => {
+                assert!(tcx.is_static(def_id));
                 assert!(!tcx.is_thread_local_static(def_id));
                 // Notice that every static has two `AllocId` that will resolve to the same
                 // thing here: one maps to `GlobalAlloc::Static`, this is the "lazy" ID,
@@ -448,29 +485,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
                 // The `GlobalAlloc::Memory` branch here is still reachable though; when a static
                 // contains a reference to memory that was created during its evaluation (i.e., not
                 // to another static), those inner references only exist in "resolved" form.
-                //
-                // Assumes `id` is already canonical.
                 if tcx.is_foreign_item(def_id) {
-                    trace!("get_global_alloc: foreign item {:?}", def_id);
-                    throw_unsup!(ReadForeignStatic(def_id))
+                    throw_unsup!(ReadExternStatic(def_id));
                 }
-                trace!("get_global_alloc: Need to compute {:?}", def_id);
-                let instance = Instance::mono(tcx, def_id);
-                let gid = GlobalId { instance, promoted: None };
-                // Use the raw query here to break validation cycles. Later uses of the static
-                // will call the full query anyway.
-                let raw_const =
-                    tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid)).map_err(|err| {
-                        // no need to report anything, the const_eval call takes care of that
-                        // for statics
-                        assert!(tcx.is_static(def_id));
-                        err
-                    })?;
-                // Make sure we use the ID of the resolved memory, not the lazy one!
-                let id = raw_const.alloc_id;
-                let allocation = tcx.global_alloc(id).unwrap_memory();
-
-                (allocation, Some(def_id))
+
+                (get_static(tcx, def_id)?, Some(def_id))
             }
         };
         M::before_access_global(memory_extra, id, alloc, def_id, is_write)?;
@@ -482,6 +501,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             alloc,
             M::GLOBAL_KIND.map(MemoryKind::Machine),
         );
+        // Sanity check that this is the same pointer we would have gotten via `global_base_pointer`.
         debug_assert_eq!(tag, M::tag_global_base_pointer(memory_extra, id));
         Ok(alloc)
     }
@@ -492,7 +512,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         &self,
         id: AllocId,
     ) -> InterpResult<'tcx, &Allocation<M::PointerTag, M::AllocExtra>> {
-        let id = M::canonical_alloc_id(self, id);
         // The error type of the inner closure here is somewhat funny.  We have two
         // ways of "erroring": An actual error, or because we got a reference from
         // `get_global_alloc` that we can actually use directly without inserting anything anywhere.
@@ -529,7 +548,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         &mut self,
         id: AllocId,
     ) -> InterpResult<'tcx, &mut Allocation<M::PointerTag, M::AllocExtra>> {
-        let id = M::canonical_alloc_id(self, id);
         let tcx = self.tcx;
         let memory_extra = &self.extra;
         let a = self.alloc_map.get_mut_or(id, || {
@@ -568,7 +586,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         id: AllocId,
         liveness: AllocCheck,
     ) -> InterpResult<'static, (Size, Align)> {
-        let id = M::canonical_alloc_id(self, id);
         // # Regular allocations
         // Don't use `self.get_raw` here as that will
         // a) cause cycles in case `id` refers to a static
@@ -621,7 +638,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         }
     }
 
-    /// Assumes `id` is already canonical.
     fn get_fn_alloc(&self, id: AllocId) -> Option<FnVal<'tcx, M::ExtraFnVal>> {
         trace!("reading fn ptr: {}", id);
         if let Some(extra) = self.extra_fn_ptr_map.get(&id) {
@@ -642,8 +658,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         if ptr.offset.bytes() != 0 {
             throw_ub!(InvalidFunctionPointer(ptr.erase_tag()))
         }
-        let id = M::canonical_alloc_id(self, ptr.alloc_id);
-        self.get_fn_alloc(id).ok_or_else(|| err_ub!(InvalidFunctionPointer(ptr.erase_tag())).into())
+        self.get_fn_alloc(ptr.alloc_id)
+            .ok_or_else(|| err_ub!(InvalidFunctionPointer(ptr.erase_tag())).into())
     }
 
     pub fn mark_immutable(&mut self, id: AllocId) -> InterpResult<'tcx> {

src/librustc_mir/interpret/mod.rs

@@ -20,7 +20,7 @@ pub use rustc_middle::mir::interpret::*; // have all the `interpret` symbols in
 pub use self::eval_context::{Frame, InterpCx, LocalState, LocalValue, StackPopCleanup};
 pub use self::intern::{intern_const_alloc_recursive, InternKind};
 pub use self::machine::{compile_time_machine, AllocMap, Machine, MayLeak, StackPopJump};
-pub use self::memory::{AllocCheck, FnVal, Memory, MemoryKind};
+pub use self::memory::{get_static, AllocCheck, FnVal, Memory, MemoryKind};
 pub use self::operand::{ImmTy, Immediate, OpTy, Operand};
 pub use self::place::{MPlaceTy, MemPlace, MemPlaceMeta, Place, PlaceTy};
 pub use self::validity::RefTracking;