From 91462db9f1c1b5db941c22efb64e7ec01d472911 Mon Sep 17 00:00:00 2001
From: Samrat Man Singh <samratmansingh@gmail.com>
Date: Sun, 26 Apr 2020 08:58:22 +0530
Subject: [PATCH 1/3] [miri] Throw UB if target size and data size don't match

If an extern C function is defined as

```
extern "C" {
    fn malloc(size: u32) -> *mut std::ffi::c_void;
}
```

on a 64-bit machine(ie. pointer sizes don't match), throw an undefined
behaviour.
---
 src/librustc_middle/mir/interpret/error.rs | 10 ++++++++++
 src/librustc_middle/mir/interpret/value.rs |  7 ++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/librustc_middle/mir/interpret/error.rs b/src/librustc_middle/mir/interpret/error.rs
index 2510dbcea0bdc..71a9382bc65c4 100644
--- a/src/librustc_middle/mir/interpret/error.rs
+++ b/src/librustc_middle/mir/interpret/error.rs
@@ -361,6 +361,11 @@ pub enum UndefinedBehaviorInfo {
     InvalidUndefBytes(Option<Pointer>),
     /// Working with a local that is not currently live.
     DeadLocal,
+    /// Data size is not equal to target size
+    ArgumentSizeMismatch {
+        target_size: u64,
+        data_size: u64,
+    },
 }
 
 impl fmt::Debug for UndefinedBehaviorInfo {
@@ -422,6 +427,11 @@ impl fmt::Debug for UndefinedBehaviorInfo {
                 "using uninitialized data, but this operation requires initialized memory"
             ),
             DeadLocal => write!(f, "accessing a dead local variable"),
+            ArgumentSizeMismatch { target_size, data_size } => write!(
+                f,
+                "argument size mismatch: expected {} bytes but got {} bytes instead",
+                target_size, data_size
+            ),
         }
     }
 }
diff --git a/src/librustc_middle/mir/interpret/value.rs b/src/librustc_middle/mir/interpret/value.rs
index f3c1c87dad484..c11e50015087b 100644
--- a/src/librustc_middle/mir/interpret/value.rs
+++ b/src/librustc_middle/mir/interpret/value.rs
@@ -393,7 +393,12 @@ impl<'tcx, Tag> Scalar<Tag> {
         assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
         match self {
             Scalar::Raw { data, size } => {
-                assert_eq!(target_size.bytes(), u64::from(size));
+                if target_size.bytes() != u64::from(size) {
+                    throw_ub!(ArgumentSizeMismatch {
+                        target_size: target_size.bytes(),
+                        data_size: u64::from(size)
+                    });
+                }
                 Scalar::check_data(data, size);
                 Ok(data)
             }

From b8af409a51138d46951d4fc49d3d2edd3346ecd5 Mon Sep 17 00:00:00 2001
From: Samrat Man Singh <samratmansingh@gmail.com>
Date: Sun, 26 Apr 2020 20:11:14 +0530
Subject: [PATCH 2/3] Rename ArgumentSizeMismatch to ScalarSizeMismatch

---
 src/librustc_middle/mir/interpret/error.rs | 6 +++---
 src/librustc_middle/mir/interpret/value.rs | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/librustc_middle/mir/interpret/error.rs b/src/librustc_middle/mir/interpret/error.rs
index 71a9382bc65c4..875b514e8c81f 100644
--- a/src/librustc_middle/mir/interpret/error.rs
+++ b/src/librustc_middle/mir/interpret/error.rs
@@ -362,7 +362,7 @@ pub enum UndefinedBehaviorInfo {
     /// Working with a local that is not currently live.
     DeadLocal,
     /// Data size is not equal to target size
-    ArgumentSizeMismatch {
+    ScalarSizeMismatch {
         target_size: u64,
         data_size: u64,
     },
@@ -427,9 +427,9 @@ impl fmt::Debug for UndefinedBehaviorInfo {
                 "using uninitialized data, but this operation requires initialized memory"
             ),
             DeadLocal => write!(f, "accessing a dead local variable"),
-            ArgumentSizeMismatch { target_size, data_size } => write!(
+            ScalarSizeMismatch { target_size, data_size } => write!(
                 f,
-                "argument size mismatch: expected {} bytes but got {} bytes instead",
+                "scalar size mismatch: expected {} bytes but got {} bytes instead",
                 target_size, data_size
             ),
         }
diff --git a/src/librustc_middle/mir/interpret/value.rs b/src/librustc_middle/mir/interpret/value.rs
index c11e50015087b..6e013f75ed759 100644
--- a/src/librustc_middle/mir/interpret/value.rs
+++ b/src/librustc_middle/mir/interpret/value.rs
@@ -394,9 +394,9 @@ impl<'tcx, Tag> Scalar<Tag> {
         match self {
             Scalar::Raw { data, size } => {
                 if target_size.bytes() != u64::from(size) {
-                    throw_ub!(ArgumentSizeMismatch {
+                    throw_ub!(ScalarSizeMismatch {
                         target_size: target_size.bytes(),
-                        data_size: u64::from(size)
+                        data_size: u64::from(size),
                     });
                 }
                 Scalar::check_data(data, size);

From c8d8c42d1ce10d945bcd8cbff3ac9858fc909abc Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 26 Apr 2020 18:44:38 +0200
Subject: [PATCH 3/3] Adjust style

---
 src/librustc_middle/mir/interpret/error.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_middle/mir/interpret/error.rs b/src/librustc_middle/mir/interpret/error.rs
index 875b514e8c81f..785aadc11faed 100644
--- a/src/librustc_middle/mir/interpret/error.rs
+++ b/src/librustc_middle/mir/interpret/error.rs
@@ -361,7 +361,7 @@ pub enum UndefinedBehaviorInfo {
     InvalidUndefBytes(Option<Pointer>),
     /// Working with a local that is not currently live.
     DeadLocal,
-    /// Data size is not equal to target size
+    /// Data size is not equal to target size.
     ScalarSizeMismatch {
         target_size: u64,
         data_size: u64,