Rollup merge of #110782 - matthiaskrgr:revert_panic_oom, r=Amanieu

Revert panic oom

This temporarily reverts https://github.com/rust-lang/rust/pull/109507 until https://github.com/rust-lang/rust/issues/110771 is addressed

r? `@Amanieu`

4 files changed, 93 insertions, 29 deletions

diff --git a/library/std/src/alloc.rs b/library/std/src/alloc.rs
index 448a8edc291..c5a5991cc81 100644
--- a/library/std/src/alloc.rs
+++ b/library/std/src/alloc.rs
@@ -57,8 +57,9 @@
 #![stable(feature = "alloc_module", since = "1.28.0")]
 
 use core::intrinsics;
-use core::ptr;
 use core::ptr::NonNull;
+use core::sync::atomic::{AtomicPtr, Ordering};
+use core::{mem, ptr};
 
 #[stable(feature = "alloc_module", since = "1.28.0")]
 #[doc(inline)]
@@ -285,6 +286,76 @@ unsafe impl Allocator for System {
     }
 }
 
+static HOOK: AtomicPtr<()> = AtomicPtr::new(ptr::null_mut());
+
+/// Registers a custom allocation error hook, replacing any that was previously registered.
+///
+/// The allocation error hook is invoked when an infallible memory allocation fails, before
+/// the runtime aborts. The default hook prints a message to standard error,
+/// but this behavior can be customized with the [`set_alloc_error_hook`] and
+/// [`take_alloc_error_hook`] functions.
+///
+/// The hook is provided with a `Layout` struct which contains information
+/// about the allocation that failed.
+///
+/// The allocation error hook is a global resource.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(alloc_error_hook)]
+///
+/// use std::alloc::{Layout, set_alloc_error_hook};
+///
+/// fn custom_alloc_error_hook(layout: Layout) {
+///    panic!("memory allocation of {} bytes failed", layout.size());
+/// }
+///
+/// set_alloc_error_hook(custom_alloc_error_hook);
+/// ```
+#[unstable(feature = "alloc_error_hook", issue = "51245")]
+pub fn set_alloc_error_hook(hook: fn(Layout)) {
+    HOOK.store(hook as *mut (), Ordering::SeqCst);
+}
+
+/// Unregisters the current allocation error hook, returning it.
+///
+/// *See also the function [`set_alloc_error_hook`].*
+///
+/// If no custom hook is registered, the default hook will be returned.
+#[unstable(feature = "alloc_error_hook", issue = "51245")]
+pub fn take_alloc_error_hook() -> fn(Layout) {
+    let hook = HOOK.swap(ptr::null_mut(), Ordering::SeqCst);
+    if hook.is_null() { default_alloc_error_hook } else { unsafe { mem::transmute(hook) } }
+}
+
+fn default_alloc_error_hook(layout: Layout) {
+    extern "Rust" {
+        // This symbol is emitted by rustc next to __rust_alloc_error_handler.
+        // Its value depends on the -Zoom={panic,abort} compiler option.
+        static __rust_alloc_error_handler_should_panic: u8;
+    }
+
+    #[allow(unused_unsafe)]
+    if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
+        panic!("memory allocation of {} bytes failed", layout.size());
+    } else {
+        rtprintpanic!("memory allocation of {} bytes failed\n", layout.size());
+    }
+}
+
+#[cfg(not(test))]
+#[doc(hidden)]
+#[alloc_error_handler]
+#[unstable(feature = "alloc_internals", issue = "none")]
+pub fn rust_oom(layout: Layout) -> ! {
+    let hook = HOOK.load(Ordering::SeqCst);
+    let hook: fn(Layout) =
+        if hook.is_null() { default_alloc_error_hook } else { unsafe { mem::transmute(hook) } };
+    hook(layout);
+    crate::process::abort()
+}
+
 #[cfg(not(test))]
 #[doc(hidden)]
 #[allow(unused_attributes)]
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 933f75d638b..318a46d1b63 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -236,6 +236,7 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![feature(alloc_error_handler)]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]
 #![feature(allow_internal_unstable)]
@@ -319,7 +320,6 @@
 #![feature(get_mut_unchecked)]
 #![feature(map_try_insert)]
 #![feature(new_uninit)]
-#![feature(panic_oom_payload)]
 #![feature(slice_concat_trait)]
 #![feature(thin_box)]
 #![feature(try_reserve_kind)]
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
index ca4cf68ad54..a46a29cbad6 100644
--- a/library/std/src/panicking.rs
+++ b/library/std/src/panicking.rs
@@ -245,24 +245,19 @@ fn default_hook(info: &PanicInfo<'_>) {
 
     // The current implementation always returns `Some`.
     let location = info.location().unwrap();
+
+    let msg = match info.payload().downcast_ref::<&'static str>() {
+        Some(s) => *s,
+        None => match info.payload().downcast_ref::<String>() {
+            Some(s) => &s[..],
+            None => "Box<dyn Any>",
+        },
+    };
     let thread = thread_info::current_thread();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
     let write = |err: &mut dyn crate::io::Write| {
-        // Use the panic message directly if available, otherwise take it from
-        // the payload.
-        if let Some(msg) = info.message() {
-            let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
-        } else {
-            let msg = if let Some(s) = info.payload().downcast_ref::<&'static str>() {
-                *s
-            } else if let Some(s) = info.payload().downcast_ref::<String>() {
-                &s[..]
-            } else {
-                "Box<dyn Any>"
-            };
-            let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
-        }
+        let _ = writeln!(err, "thread '{name}' panicked at '{msg}', {location}");
 
         static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
@@ -529,8 +524,6 @@ pub fn panicking() -> bool {
 #[cfg(not(test))]
 #[panic_handler]
 pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
-    use alloc::alloc::AllocErrorPanicPayload;
-
     struct PanicPayload<'a> {
         inner: &'a fmt::Arguments<'a>,
         string: Option<String>,
@@ -557,7 +550,8 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
             // We do two allocations here, unfortunately. But (a) they're required with the current
-            // scheme, and (b) OOM uses its own separate payload type which doesn't allocate.
+            // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
+            // begin_panic below).
             let contents = mem::take(self.fill());
             Box::into_raw(Box::new(contents))
         }
@@ -582,14 +576,7 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     let loc = info.location().unwrap(); // The current implementation always returns Some
     let msg = info.message().unwrap(); // The current implementation always returns Some
     crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
-        if let Some(payload) = info.payload().downcast_ref::<AllocErrorPanicPayload>() {
-            rust_panic_with_hook(
-                &mut payload.internal_clone(),
-                info.message(),
-                loc,
-                info.can_unwind(),
-            );
-        } else if let Some(msg) = msg.as_str() {
+        if let Some(msg) = msg.as_str() {
             rust_panic_with_hook(&mut StrPanicPayload(msg), info.message(), loc, info.can_unwind());
         } else {
             rust_panic_with_hook(
@@ -636,7 +623,11 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
 
     unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
-            // Note that this should be the only allocation performed in this code path.
+            // Note that this should be the only allocation performed in this code path. Currently
+            // this means that panic!() on OOM will invoke this code path, but then again we're not
+            // really ready for panic on OOM anyway. If we do start doing this, then we should
+            // propagate this allocation to be performed in the parent of this thread instead of the
+            // thread that's panicking.
             let data = match self.inner.take() {
                 Some(a) => Box::new(a) as Box<dyn Any + Send>,
                 None => process::abort(),
diff --git a/library/std/src/prelude/v1.rs b/library/std/src/prelude/v1.rs
index 4f325a70b18..2aefd7c513d 100644
--- a/library/std/src/prelude/v1.rs
+++ b/library/std/src/prelude/v1.rs
@@ -60,7 +60,9 @@ pub use core::prelude::v1::{RustcDecodable, RustcEncodable};
 // Do not `doc(no_inline)` so that they become doc items on their own
 // (no public module for them to be re-exported from).
 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
-pub use core::prelude::v1::{bench, derive, global_allocator, test, test_case};
+pub use core::prelude::v1::{
+    alloc_error_handler, bench, derive, global_allocator, test, test_case,
+};
 
 #[unstable(feature = "derive_const", issue = "none")]
 pub use core::prelude::v1::derive_const;