Auto merge of #105997 - RalfJung:immediate-abort, r=eholk

abort immediately on bad mem::zeroed/uninit

Now that we have non-unwinding panics, let's use them for these assertions. This re-establishes the property that `mem::uninitialized` and `mem::zeroed` will never unwind -- the earlier approach of causing panics here sometimes led to hard-to-debug segfaults when the surrounding code was not able to cope with the unexpected unwinding.

Cc `@bjorn3` I did not touch cranelift but I assume it needs a similar patch. However it has a `codegen_panic` abstraction that I did not want to touch since I didn't know how else it is used.

Author: bors

core/src/intrinsics.rs

@@ -2281,7 +2281,7 @@ macro_rules! assert_unsafe_precondition {
             fn runtime$(<$($tt)*>)?($($i:$ty),*) {
                 if !$e {
                     // don't unwind to reduce impact on code size
-                    ::core::panicking::panic_str_nounwind(
+                    ::core::panicking::panic_nounwind(
                         concat!("unsafe precondition(s) violated: ", $name)
                     );
                 }

core/src/panicking.rs

@@ -64,12 +64,13 @@ pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
     unsafe { panic_impl(&pi) }
 }
 
-/// Like panic_fmt, but without unwinding and track_caller to reduce the impact on codesize.
-/// Also just works on `str`, as a `fmt::Arguments` needs more space to be passed.
+/// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize.
+/// (No `fmt` variant as a `fmt::Arguments` needs more space to be passed.)
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cfg_attr(not(bootstrap), lang = "panic_nounwind")] // needed by codegen for non-unwinding panics
 #[rustc_nounwind]
-pub fn panic_str_nounwind(msg: &'static str) -> ! {
+pub fn panic_nounwind(msg: &'static str) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         super::intrinsics::abort()
     }
@@ -153,10 +154,11 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 /// any extra arguments (including those synthesized by track_caller).
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
-#[lang = "panic_no_unwind"] // needed by codegen for panic in nounwind function
+#[cfg_attr(bootstrap, lang = "panic_no_unwind")] // needed by codegen for panic in nounwind function
+#[cfg_attr(not(bootstrap), lang = "panic_cannot_unwind")] // needed by codegen for panic in nounwind function
 #[rustc_nounwind]
-fn panic_no_unwind() -> ! {
-    panic_str_nounwind("panic in a function that cannot unwind")
+fn panic_cannot_unwind() -> ! {
+    panic_nounwind("panic in a function that cannot unwind")
 }
 
 /// This function is used instead of panic_fmt in const eval.