Rollup merge of #132801 - RalfJung:alloc-mutability, r=oli-obk

interpret: get_alloc_info: also return mutability

This will be needed for rust-lang#3971

This then tuned into a larger refactor where we introduce a new type for the `get_alloc_info` return data, and we move some code to methods on `GlobalAlloc` to avoid duplicating it between the validity check and `get_alloc_info`.

src/alloc_addresses/mod.rs

@@ -134,7 +134,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 // entered for addresses that are not the base address, so even zero-sized
                 // allocations will get recognized at their base address -- but all other
                 // allocations will *not* be recognized at their "end" address.
-                let size = ecx.get_alloc_info(alloc_id).0;
+                let size = ecx.get_alloc_info(alloc_id).size;
                 if offset < size.bytes() { Some(alloc_id) } else { None }
             }
         }?;
@@ -157,25 +157,25 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
     ) -> InterpResult<'tcx, u64> {
         let ecx = self.eval_context_ref();
         let mut rng = ecx.machine.rng.borrow_mut();
-        let (size, align, kind) = ecx.get_alloc_info(alloc_id);
+        let info = ecx.get_alloc_info(alloc_id);
         // This is either called immediately after allocation (and then cached), or when
         // adjusting `tcx` pointers (which never get freed). So assert that we are looking
         // at a live allocation. This also ensures that we never re-assign an address to an
         // allocation that previously had an address, but then was freed and the address
         // information was removed.
-        assert!(!matches!(kind, AllocKind::Dead));
+        assert!(!matches!(info.kind, AllocKind::Dead));
 
         // This allocation does not have a base address yet, pick or reuse one.
         if ecx.machine.native_lib.is_some() {
             // In native lib mode, we use the "real" address of the bytes for this allocation.
             // This ensures the interpreted program and native code have the same view of memory.
-            let base_ptr = match kind {
+            let base_ptr = match info.kind {
                 AllocKind::LiveData => {
                     if ecx.tcx.try_get_global_alloc(alloc_id).is_some() {
                         // For new global allocations, we always pre-allocate the memory to be able use the machine address directly.
-                        let prepared_bytes = MiriAllocBytes::zeroed(size, align)
+                        let prepared_bytes = MiriAllocBytes::zeroed(info.size, info.align)
                             .unwrap_or_else(|| {
-                                panic!("Miri ran out of memory: cannot create allocation of {size:?} bytes")
+                                panic!("Miri ran out of memory: cannot create allocation of {size:?} bytes", size = info.size)
                             });
                         let ptr = prepared_bytes.as_ptr();
                         // Store prepared allocation space to be picked up for use later.
@@ -204,7 +204,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
         }
         // We are not in native lib mode, so we control the addresses ourselves.
         if let Some((reuse_addr, clock)) =
-            global_state.reuse.take_addr(&mut *rng, size, align, memory_kind, ecx.active_thread())
+            global_state.reuse.take_addr(&mut *rng, info.size, info.align, memory_kind, ecx.active_thread())
         {
             if let Some(clock) = clock {
                 ecx.acquire_clock(&clock);
@@ -220,14 +220,14 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 .next_base_addr
                 .checked_add(slack)
                 .ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
-            let base_addr = align_addr(base_addr, align.bytes());
+            let base_addr = align_addr(base_addr, info.align.bytes());
 
             // Remember next base address.  If this allocation is zero-sized, leave a gap of at
             // least 1 to avoid two allocations having the same base address. (The logic in
             // `alloc_id_from_addr` assumes unique addresses, and different function/vtable pointers
             // need to be distinguishable!)
             global_state.next_base_addr = base_addr
-                .checked_add(max(size.bytes(), 1))
+                .checked_add(max(info.size.bytes(), 1))
                 .ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
             // Even if `Size` didn't overflow, we might still have filled up the address space.
             if global_state.next_base_addr > ecx.target_usize_max() {

src/borrow_tracker/mod.rs

@@ -363,7 +363,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             // If it does exist, then we have the guarantee that the
             // pointer is readable, and the implicit read access inserted
             // will never cause UB on the pointer itself.
-            let (_, _, kind) = this.get_alloc_info(*alloc_id);
+            let kind = this.get_alloc_info(*alloc_id).kind;
             if matches!(kind, AllocKind::LiveData) {
                 let alloc_extra = this.get_alloc_extra(*alloc_id)?; // can still fail for `extern static`
                 let alloc_borrow_tracker = &alloc_extra.borrow_tracker.as_ref().unwrap();

src/borrow_tracker/stacked_borrows/mod.rs

@@ -626,7 +626,7 @@ trait EvalContextPrivExt<'tcx, 'ecx>: crate::MiriInterpCxExt<'tcx> {
                 return interp_ok(())
             };
 
-            let (_size, _align, alloc_kind) = this.get_alloc_info(alloc_id);
+            let alloc_kind = this.get_alloc_info(alloc_id).kind;
             match alloc_kind {
                 AllocKind::LiveData => {
                     // This should have alloc_extra data, but `get_alloc_extra` can still fail
@@ -1017,7 +1017,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         // Function pointers and dead objects don't have an alloc_extra so we ignore them.
         // This is okay because accessing them is UB anyway, no need for any Stacked Borrows checks.
         // NOT using `get_alloc_extra_mut` since this might be a read-only allocation!
-        let (_size, _align, kind) = this.get_alloc_info(alloc_id);
+        let kind = this.get_alloc_info(alloc_id).kind;
         match kind {
             AllocKind::LiveData => {
                 // This should have alloc_extra data, but `get_alloc_extra` can still fail

src/borrow_tracker/tree_borrows/mod.rs

@@ -274,7 +274,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 .insert(new_tag, protect);
         }
 
-        let alloc_kind = this.get_alloc_info(alloc_id).2;
+        let alloc_kind = this.get_alloc_info(alloc_id).kind;
         if !matches!(alloc_kind, AllocKind::LiveData) {
             assert_eq!(ptr_size, Size::ZERO); // we did the deref check above, size has to be 0 here
             // There's not actually any bytes here where accesses could even be tracked.
@@ -538,7 +538,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         // Function pointers and dead objects don't have an alloc_extra so we ignore them.
         // This is okay because accessing them is UB anyway, no need for any Tree Borrows checks.
         // NOT using `get_alloc_extra_mut` since this might be a read-only allocation!
-        let (_size, _align, kind) = this.get_alloc_info(alloc_id);
+        let kind = this.get_alloc_info(alloc_id).kind;
         match kind {
             AllocKind::LiveData => {
                 // This should have alloc_extra data, but `get_alloc_extra` can still fail

src/machine.rs

@@ -1125,10 +1125,10 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
             let Provenance::Concrete { alloc_id, .. } = ptr.provenance else {
                 panic!("extern_statics cannot contain wildcards")
             };
-            let (shim_size, shim_align, _kind) = ecx.get_alloc_info(alloc_id);
+            let info = ecx.get_alloc_info(alloc_id);
             let def_ty = ecx.tcx.type_of(def_id).instantiate_identity();
             let extern_decl_layout = ecx.tcx.layout_of(ty::ParamEnv::empty().and(def_ty)).unwrap();
-            if extern_decl_layout.size != shim_size || extern_decl_layout.align.abi != shim_align {
+            if extern_decl_layout.size != info.size || extern_decl_layout.align.abi != info.align {
                 throw_unsup_format!(
                     "extern static `{link_name}` has been declared as `{krate}::{name}` \
                     with a size of {decl_size} bytes and alignment of {decl_align} bytes, \
@@ -1138,8 +1138,8 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
                     krate = ecx.tcx.crate_name(def_id.krate),
                     decl_size = extern_decl_layout.size.bytes(),
                     decl_align = extern_decl_layout.align.abi.bytes(),
-                    shim_size = shim_size.bytes(),
-                    shim_align = shim_align.bytes(),
+                    shim_size = info.size.bytes(),
+                    shim_align = info.align.bytes(),
                 )
             }
             interp_ok(ptr)

src/shims/foreign_items.rs

@@ -300,7 +300,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let id = this.read_scalar(id)?.to_u64()?;
                 let show_unnamed = this.read_scalar(show_unnamed)?.to_bool()?;
                 if let Some(id) = std::num::NonZero::new(id).map(AllocId)
-                    && this.get_alloc_info(id).2 == AllocKind::LiveData
+                    && this.get_alloc_info(id).kind == AllocKind::LiveData
                 {
                     this.print_borrow_state(id, show_unnamed)?;
                 } else {
@@ -409,7 +409,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     );
                 }
                 if let Ok((alloc_id, offset, ..)) = this.ptr_try_get_alloc_id(ptr, 0) {
-                    let (_size, alloc_align, _kind) = this.get_alloc_info(alloc_id);
+                    let alloc_align = this.get_alloc_info(alloc_id).align;
                     // If the newly promised alignment is bigger than the native alignment of this
                     // allocation, and bigger than the previously promised alignment, then set it.
                     if align > alloc_align