From 5640304c63c5c77b721424be88791503a0e0ea3d Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 17 Apr 2022 17:26:15 -0400
Subject: [PATCH 1/3] add log warnings for when we overwrite parts of a
 pointer, and de-init the rest

---
 compiler/rustc_middle/src/mir/interpret/allocation.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/compiler/rustc_middle/src/mir/interpret/allocation.rs b/compiler/rustc_middle/src/mir/interpret/allocation.rs
index 438f356f072c6..357e67de7575a 100644
--- a/compiler/rustc_middle/src/mir/interpret/allocation.rs
+++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs
@@ -509,6 +509,9 @@ impl<Tag: Copy, Extra> Allocation<Tag, Extra> {
             if Tag::ERR_ON_PARTIAL_PTR_OVERWRITE {
                 return Err(AllocError::PartialPointerOverwrite(first));
             }
+            warn!(
+                "Partial pointer overwrite! De-initializing memory at offsets {first:?}..{start:?}."
+            );
             self.init_mask.set_range(first, start, false);
         }
         if last > end {
@@ -517,10 +520,15 @@ impl<Tag: Copy, Extra> Allocation<Tag, Extra> {
                     last - cx.data_layout().pointer_size,
                 ));
             }
+            warn!(
+                "Partial pointer overwrite! De-initializing memory at offsets {end:?}..{last:?}."
+            );
             self.init_mask.set_range(end, last, false);
         }
 
         // Forget all the relocations.
+        // Since relocations do not overlap, we know that removing until `last` (exclusive) is fine,
+        // i.e., this will not remove any other relocations just after the ones we care about.
         self.relocations.0.remove_range(first..last);
 
         Ok(())

From 989e7479d9cbd285c8104a5bbd9159ff2d66188f Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 17 Apr 2022 18:07:19 -0400
Subject: [PATCH 2/3] interpret: more debug logging for read_scalar and
 write_scalar

---
 .../rustc_const_eval/src/interpret/memory.rs  | 25 ++++++++++++++++---
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index a165fa23f30ac..6504624ad67c5 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -877,9 +877,17 @@ impl<'tcx, 'a, Tag: Provenance, Extra> AllocRefMut<'a, 'tcx, Tag, Extra> {
         range: AllocRange,
         val: ScalarMaybeUninit<Tag>,
     ) -> InterpResult<'tcx> {
+        let range = self.range.subrange(range);
+        debug!(
+            "write_scalar in {} at {:#x}, size {}: {:?}",
+            self.alloc_id,
+            range.start.bytes(),
+            range.size.bytes(),
+            val
+        );
         Ok(self
             .alloc
-            .write_scalar(&self.tcx, self.range.subrange(range), val)
+            .write_scalar(&self.tcx, range, val)
             .map_err(|e| e.to_interp_error(self.alloc_id))?)
     }
 
@@ -899,10 +907,19 @@ impl<'tcx, 'a, Tag: Provenance, Extra> AllocRefMut<'a, 'tcx, Tag, Extra> {
 
 impl<'tcx, 'a, Tag: Provenance, Extra> AllocRef<'a, 'tcx, Tag, Extra> {
     pub fn read_scalar(&self, range: AllocRange) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {
-        Ok(self
+        let range = self.range.subrange(range);
+        let res = self
             .alloc
-            .read_scalar(&self.tcx, self.range.subrange(range))
-            .map_err(|e| e.to_interp_error(self.alloc_id))?)
+            .read_scalar(&self.tcx, range)
+            .map_err(|e| e.to_interp_error(self.alloc_id))?;
+        debug!(
+            "read_scalar in {} at {:#x}, size {}: {:?}",
+            self.alloc_id,
+            range.start.bytes(),
+            range.size.bytes(),
+            res
+        );
+        Ok(res)
     }
 
     pub fn read_ptr_sized(&self, offset: Size) -> InterpResult<'tcx, ScalarMaybeUninit<Tag>> {

From f3bdcfb8b08a14a556caa3d1adae835c8bfd8c58 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 17 Apr 2022 18:45:01 -0400
Subject: [PATCH 3/3] downgrade really verbose logging to trace

---
 compiler/rustc_const_eval/src/interpret/eval_context.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index f0fff602fe4cf..827959113b907 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -679,7 +679,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         return_place: Option<&PlaceTy<'tcx, M::PointerTag>>,
         return_to_block: StackPopCleanup,
     ) -> InterpResult<'tcx> {
-        debug!("body: {:#?}", body);
+        trace!("body: {:#?}", body);
         // first push a stack frame so we have access to the local substs
         let pre_frame = Frame {
             body,
@@ -836,7 +836,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             return Ok(());
         }
 
-        debug!("locals: {:#?}", frame.locals);
+        trace!("locals: {:#?}", frame.locals);
 
         // Cleanup: deallocate all locals that are backed by an allocation.
         for local in &frame.locals {