Rollup merge of rust-lang#62103 - RalfJung:debug-assert, r=alexcrichton

Add debug assertions to write_bytes and copy*

Looks like @nitnelave  went MIA in rust-lang#58783, so I am re-submitting their PR, tweaked just a bit. I took care to preserve commit authorship.

Cc rust-lang#53871

Author: Mark-Simulacrum

src/libcore/intrinsics.rs

@@ -36,6 +36,8 @@
             issue = "0")]
 #![allow(missing_docs)]
 
+use crate::mem;
+
 #[stable(feature = "drop_in_place", since = "1.8.0")]
 #[rustc_deprecated(reason = "no longer an intrinsic - use `ptr::drop_in_place` directly",
                    since = "1.18.0")]
@@ -1331,6 +1333,26 @@ extern "rust-intrinsic" {
 // (`transmute` also falls into this category, but it cannot be wrapped due to the
 // check that `T` and `U` have the same size.)
 
+/// Checks whether `ptr` is properly aligned with respect to
+/// `align_of::<T>()`.
+pub(crate) fn is_aligned_and_not_null<T>(ptr: *const T) -> bool {
+    !ptr.is_null() && ptr as usize % mem::align_of::<T>() == 0
+}
+
+/// Checks whether the regions of memory starting at `src` and `dst` of size
+/// `count * size_of::<T>()` overlap.
+fn overlaps<T>(src: *const T, dst: *const T, count: usize) -> bool {
+    let src_usize = src as usize;
+    let dst_usize = dst as usize;
+    let size = mem::size_of::<T>().checked_mul(count).unwrap();
+    let diff = if src_usize > dst_usize {
+        src_usize - dst_usize
+    } else {
+        dst_usize - src_usize
+    };
+    size > diff
+}
+
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
 /// and destination must *not* overlap.
 ///
@@ -1420,7 +1442,11 @@ pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
     extern "rust-intrinsic" {
         fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
     }
-    copy_nonoverlapping(src, dst, count);
+
+    debug_assert!(is_aligned_and_not_null(src), "attempt to copy from unaligned or null pointer");
+    debug_assert!(is_aligned_and_not_null(dst), "attempt to copy to unaligned or null pointer");
+    debug_assert!(!overlaps(src, dst, count), "attempt to copy to overlapping memory");
+    copy_nonoverlapping(src, dst, count)
 }
 
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
@@ -1480,6 +1506,9 @@ pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
     extern "rust-intrinsic" {
         fn copy<T>(src: *const T, dst: *mut T, count: usize);
     }
+
+    debug_assert!(is_aligned_and_not_null(src), "attempt to copy from unaligned or null pointer");
+    debug_assert!(is_aligned_and_not_null(dst), "attempt to copy to unaligned or null pointer");
     copy(src, dst, count)
 }
 
@@ -1561,6 +1590,8 @@ pub unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
     extern "rust-intrinsic" {
         fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
     }
+
+    debug_assert!(is_aligned_and_not_null(dst), "attempt to write to unaligned or null pointer");
     write_bytes(dst, val, count)
 }
 

src/libcore/slice/mod.rs

@@ -25,7 +25,7 @@
 use crate::cmp::Ordering::{self, Less, Equal, Greater};
 use crate::cmp;
 use crate::fmt;
-use crate::intrinsics::{assume, exact_div, unchecked_sub};
+use crate::intrinsics::{assume, exact_div, unchecked_sub, is_aligned_and_not_null};
 use crate::isize;
 use crate::iter::*;
 use crate::ops::{FnMut, Try, self};
@@ -5228,7 +5228,7 @@ unsafe impl<'a, T> TrustedRandomAccess for RChunksExactMut<'a, T> {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
-    debug_assert!(data as usize % mem::align_of::<T>() == 0, "attempt to create unaligned slice");
+    debug_assert!(is_aligned_and_not_null(data), "attempt to create unaligned or null slice");
     debug_assert!(mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize,
                   "attempt to create slice covering half the address space");
     &*ptr::slice_from_raw_parts(data, len)
@@ -5249,7 +5249,7 @@ pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
-    debug_assert!(data as usize % mem::align_of::<T>() == 0, "attempt to create unaligned slice");
+    debug_assert!(is_aligned_and_not_null(data), "attempt to create unaligned or null slice");
     debug_assert!(mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize,
                   "attempt to create slice covering half the address space");
     &mut *ptr::slice_from_raw_parts_mut(data, len)

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1736,7 +1736,9 @@ extern "C" {
     pub fn LLVMRustArchiveIteratorFree(AIR: &'a mut ArchiveIterator<'a>);
     pub fn LLVMRustDestroyArchive(AR: &'static mut Archive);
 
-    pub fn LLVMRustGetSectionName(SI: &SectionIterator<'_>, data: &mut *const c_char) -> size_t;
+    #[allow(improper_ctypes)]
+    pub fn LLVMRustGetSectionName(SI: &SectionIterator<'_>,
+                                  data: &mut Option<std::ptr::NonNull<c_char>>) -> size_t;
 
     #[allow(improper_ctypes)]
     pub fn LLVMRustWriteTwineToString(T: &Twine, s: &RustString);

src/librustc_codegen_llvm/metadata.rs

@@ -8,7 +8,6 @@ use rustc_data_structures::owning_ref::OwningRef;
 use rustc_codegen_ssa::METADATA_FILENAME;
 
 use std::path::Path;
-use std::ptr;
 use std::slice;
 use rustc_fs_util::path_to_c_string;
 
@@ -67,10 +66,16 @@ fn search_meta_section<'a>(of: &'a ObjectFile,
     unsafe {
         let si = mk_section_iter(of.llof);
         while llvm::LLVMIsSectionIteratorAtEnd(of.llof, si.llsi) == False {
-            let mut name_buf = ptr::null();
+            let mut name_buf = None;
             let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
-            let name = slice::from_raw_parts(name_buf as *const u8, name_len as usize).to_vec();
-            let name = String::from_utf8(name).unwrap();
+            let name = name_buf.map_or(
+                String::new(), // We got a NULL ptr, ignore `name_len`.
+                |buf| String::from_utf8(
+                    slice::from_raw_parts(buf.as_ptr() as *const u8,
+                                          name_len as usize)
+                    .to_vec()
+                ).unwrap()
+            );
             debug!("get_metadata_section: name {}", name);
             if read_metadata_section_name(target) == name {
                 let cbuf = llvm::LLVMGetSectionContents(si.llsi);

src/test/codegen/issue-45222.rs

@@ -1,4 +1,5 @@
 // compile-flags: -O
+// ignore-debug: the debug assertions get in the way
 
 #![crate_type = "lib"]
 

src/test/codegen/issue-45466.rs

@@ -1,4 +1,5 @@
 // compile-flags: -O
+// ignore-debug: the debug assertions get in the way
 
 #![crate_type="rlib"]
 

src/test/codegen/swap-small-types.rs

@@ -1,5 +1,6 @@
 // compile-flags: -O
 // only-x86_64
+// ignore-debug: the debug assertions get in the way
 
 #![crate_type = "lib"]