Rollup merge of rust-lang#130245 - RalfJung:miri-alloc-backtrace, r=Amanieu

make basic allocation functions track_caller in Miri for nicer backtraces

This matches what we did with basic pointer and atomic operations.

Author: Zalathar

alloc/src/alloc.rs

@@ -89,6 +89,7 @@ pub use std::alloc::Global;
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
     unsafe {
         // Make sure we don't accidentally allow omitting the allocator shim in
@@ -113,6 +114,7 @@ pub unsafe fn alloc(layout: Layout) -> *mut u8 {
 /// See [`GlobalAlloc::dealloc`].
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
     unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
 }
@@ -132,6 +134,7 @@ pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
     unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
 }
@@ -166,13 +169,15 @@ pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
     unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
 }
 
 #[cfg(not(test))]
 impl Global {
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
             0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
@@ -187,6 +192,7 @@ impl Global {
 
     // SAFETY: Same as `Allocator::grow`
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow_impl(
         &self,
         ptr: NonNull<u8>,
@@ -237,16 +243,19 @@ impl Global {
 #[cfg(not(test))]
 unsafe impl Allocator for Global {
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, false)
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, true)
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
         if layout.size() != 0 {
             // SAFETY: `layout` is non-zero in size,
@@ -256,6 +265,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow(
         &self,
         ptr: NonNull<u8>,
@@ -267,6 +277,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow_zeroed(
         &self,
         ptr: NonNull<u8>,
@@ -278,6 +289,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn shrink(
         &self,
         ptr: NonNull<u8>,
@@ -325,6 +337,7 @@ unsafe impl Allocator for Global {
 #[cfg(all(not(no_global_oom_handling), not(test)))]
 #[lang = "exchange_malloc"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
     let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
     match Global.allocate(layout) {

alloc/src/boxed.rs

@@ -250,6 +250,7 @@ impl<T> Box<T> {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     #[rustc_diagnostic_item = "box_new"]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub fn new(x: T) -> Self {
         #[rustc_box]
         Box::new(x)