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

Make __rust_alloc_error_handler_should_panic a function

Fixes rust-lang/rust#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/rust#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

src/shims/extern_static.rs

@@ -1,7 +1,5 @@
 //! Provides the `extern static` that this platform expects.
 
-use rustc_symbol_mangling::mangle_internal_symbol;
-
 use crate::*;
 
 impl<'tcx> MiriMachine<'tcx> {
@@ -45,15 +43,6 @@ impl<'tcx> MiriMachine<'tcx> {
 
     /// Sets up the "extern statics" for this machine.
     pub fn init_extern_statics(ecx: &mut MiriInterpCx<'tcx>) -> InterpResult<'tcx> {
-        // "__rust_alloc_error_handler_should_panic"
-        let val = ecx.tcx.sess.opts.unstable_opts.oom.should_panic();
-        let val = ImmTy::from_int(val, ecx.machine.layouts.u8);
-        Self::alloc_extern_static(
-            ecx,
-            &mangle_internal_symbol(*ecx.tcx, "__rust_alloc_error_handler_should_panic"),
-            val,
-        )?;
-
         if ecx.target_os_is_unix() {
             // "environ" is mandated by POSIX.
             let environ = ecx.machine.env_vars.unix().environ();

src/shims/foreign_items.rs

@@ -615,6 +615,12 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 // This is a no-op shim that only exists to prevent making the allocator shims instantly stable.
                 let [] = this.check_shim(abi, CanonAbi::Rust, link_name, args)?;
             }
+            name if name == this.mangle_internal_symbol("__rust_alloc_error_handler_should_panic_v2") => {
+                // Gets the value of the `oom` option.
+                let [] = this.check_shim(abi, CanonAbi::Rust, link_name, args)?;
+                let val = this.tcx.sess.opts.unstable_opts.oom.should_panic();
+                this.write_int(val, dest)?;
+            }
 
             // C memory handling functions
             "memcmp" => {

tests/pass/alloc-access-tracking.rs

@@ -1,7 +1,7 @@
 #![no_std]
 #![no_main]
-//@compile-flags: -Zmiri-track-alloc-id=19 -Zmiri-track-alloc-accesses -Cpanic=abort
-//@normalize-stderr-test: "id 19" -> "id $$ALLOC"
+//@compile-flags: -Zmiri-track-alloc-id=18 -Zmiri-track-alloc-accesses -Cpanic=abort
+//@normalize-stderr-test: "id 18" -> "id $$ALLOC"
 //@only-target: linux # alloc IDs differ between OSes (due to extern static allocations)
 
 extern "Rust" {