Rollup merge of rust-lang#143387 - dpaoliello:shouldpanicfn, r=bjorn3

Make __rust_alloc_error_handler_should_panic a function

Fixes rust-lang#143253

`__rust_alloc_error_handler_should_panic` is a static but was being exported as a function.

For most targets this doesn't matter, but Arm64EC Windows uses different decorations for exported variables vs functions, hence it fails to link when `-Z oom=abort` is enabled.

We've had issues in the past with statics like this (see rust-lang#141061) but the tldr; is that Arm64EC needs symbols correctly exported as either a function or data, and data MUST and MUST ONLY be marked `dllimport` when the symbol is being imported from another binary, which is non-trivial to calculate for these compiler-generated statics.

So, instead, the easiest thing to do is to make `__rust_alloc_error_handler_should_panic` a function instead.

Since `__rust_alloc_error_handler_should_panic` isn't involved in any linking shenanigans, I've marked it as `AlwaysInline` with the hopes that the various backends will see that it is just returning a constant and perform the same optimizations as the previous implementation.

r? `@bjorn3`

Author: matthiaskrgr

alloc/src/alloc.rs

@@ -429,10 +429,10 @@ pub mod __alloc_error_handler {
             // This symbol is emitted by rustc next to __rust_alloc_error_handler.
             // Its value depends on the -Zoom={panic,abort} compiler option.
             #[rustc_std_internal_symbol]
-            static __rust_alloc_error_handler_should_panic: u8;
+            fn __rust_alloc_error_handler_should_panic_v2() -> u8;
         }
 
-        if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
+        if unsafe { __rust_alloc_error_handler_should_panic_v2() != 0 } {
             panic!("memory allocation of {size} bytes failed")
         } else {
             core::panicking::panic_nounwind_fmt(

std/src/alloc.rs

@@ -349,10 +349,10 @@ fn default_alloc_error_hook(layout: Layout) {
         // This symbol is emitted by rustc next to __rust_alloc_error_handler.
         // Its value depends on the -Zoom={panic,abort} compiler option.
         #[rustc_std_internal_symbol]
-        static __rust_alloc_error_handler_should_panic: u8;
+        fn __rust_alloc_error_handler_should_panic_v2() -> u8;
     }
 
-    if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
+    if unsafe { __rust_alloc_error_handler_should_panic_v2() != 0 } {
         panic!("memory allocation of {} bytes failed", layout.size());
     } else {
         // This is the default path taken on OOM, and the only path taken on stable with std.