Auto merge of #141061 - dpaoliello:shimasfn, r=bjorn3

Change __rust_no_alloc_shim_is_unstable to be a function

This fixes a long sequence of issues:

1. A customer reported that building for Arm64EC was broken: #138541
2. This was caused by a bug in my original implementation of Arm64EC support, namely that only functions on Arm64EC need to be decorated with `#` but Rust was decorating statics as well.
3. Once I corrected Rust to only decorate functions, I started linking failures where the linker couldn't find statics exported by dylib dependencies. This was caused by the compiler not marking exported statics in the generated DEF file with `DATA`, thus they were being exported as functions not data.
4. Once I corrected the way that the DEF files were being emitted, the linker started failing saying that it couldn't find `__rust_no_alloc_shim_is_unstable`. This is because the MSVC linker requires the declarations of statics imported from other dylibs to be marked with `dllimport` (whereas it will happily link to functions imported from other dylibs whether they are marked `dllimport` or not).
5. I then made a change to ensure that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport`, but the MSVC linker started emitting warnings that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport` but was declared in an obj file. This is a harmless warning which is a performance hint: anything that's marked `dllimport` must be indirected via an `__imp` symbol so I added a linker arg in the target to suppress the warning.
6. A customer then reported a similar warning when using `lld-link` (<https://github.com/rust-lang/rust/pull/140176#issuecomment-2872448443>). I don't think it was an implementation difference between the two linkers but rather that, depending on the obj that the declaration versus uses of `__rust_no_alloc_shim_is_unstable` landed in we would get different warnings, so I suppressed that warning as well: #140954.
7. Another customer reported that they weren't using the Rust compiler to invoke the linker, thus these warnings were breaking their build: <https://github.com/rust-lang/rust/pull/140176#issuecomment-2881867433>. At that point, my original change was reverted (#141024) leaving Arm64EC broken yet again.

Taking a step back, a lot of these linker issues arise from the fact that `__rust_no_alloc_shim_is_unstable` is marked as `extern "Rust"` in the standard library and, therefore, assumed to be a foreign item from a different crate BUT the Rust compiler may choose to generate it either in the current crate, some other crate that will be statically linked in OR some other crate that will by dynamically imported.

Worse yet, it is impossible while building a given crate to know if `__rust_no_alloc_shim_is_unstable` will statically linked or dynamically imported: it might be that one of its dependent crates is the one with an allocator kind set and thus that crate (which is compiled later) will decide depending if it has any dylib dependencies or not to import `__rust_no_alloc_shim_is_unstable` or generate it. Thus, there is no way to know if the declaration of `__rust_no_alloc_shim_is_unstable` should be marked with `dllimport` or not.

There is a simple fix for all this: there is no reason `__rust_no_alloc_shim_is_unstable` must be a static. It needs to be some symbol that must be linked in; thus, it could easily be a function instead. As a function, there is no need to mark it as `dllimport` when dynamically imported which avoids the entire mess above.

There may be a perf hit for changing the `volatile load` to be a `tail call`, so I'm happy to change that part back (although I question what the codegen of a `volatile load` would look like, and if the backend is going to try to use load-acquire semantics).

Build with this change applied BEFORE #140176 was reverted to demonstrate that there are no linking issues with either MSVC or MinGW: <https://github.com/rust-lang/rust/actions/runs/15078657205>

Incidentally, I fixed `tests/run-make/no-alloc-shim` to work with MSVC as I needed it to be able to test locally (FYI for #128602)

r? `@bjorn3`
cc `@jieyouxu`

18 files changed, 155 insertions, 131 deletions

diff --git a/compiler/rustc_ast/src/expand/allocator.rs b/compiler/rustc_ast/src/expand/allocator.rs
index dd8d5ae624a..7dee2ed17b4 100644
--- a/compiler/rustc_ast/src/expand/allocator.rs
+++ b/compiler/rustc_ast/src/expand/allocator.rs
@@ -22,7 +22,7 @@ pub fn alloc_error_handler_name(alloc_error_handler_kind: AllocatorKind) -> &'st
     }
 }
 
-pub const NO_ALLOC_SHIM_IS_UNSTABLE: &str = "__rust_no_alloc_shim_is_unstable";
+pub const NO_ALLOC_SHIM_IS_UNSTABLE: &str = "__rust_no_alloc_shim_is_unstable_v2";
 
 pub enum AllocatorTy {
     Layout,
diff --git a/compiler/rustc_codegen_cranelift/src/allocator.rs b/compiler/rustc_codegen_cranelift/src/allocator.rs
index 9cff8a84db3..ffb932a3c38 100644
--- a/compiler/rustc_codegen_cranelift/src/allocator.rs
+++ b/compiler/rustc_codegen_cranelift/src/allocator.rs
@@ -1,6 +1,7 @@
 //! Allocator shim
 // Adapted from rustc
 
+use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_ast::expand::allocator::{
     ALLOCATOR_METHODS, AllocatorKind, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE,
     alloc_error_handler_name, default_fn_name, global_fn_name,
@@ -97,16 +98,31 @@ fn codegen_inner(
     data.define(Box::new([val]));
     module.define_data(data_id, &data).unwrap();
 
-    let data_id = module
-        .declare_data(
-            &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
-            Linkage::Export,
-            false,
-            false,
-        )
-        .unwrap();
-    let mut data = DataDescription::new();
-    data.set_align(1);
-    data.define(Box::new([0]));
-    module.define_data(data_id, &data).unwrap();
+    {
+        let sig = Signature {
+            call_conv: module.target_config().default_call_conv,
+            params: vec![],
+            returns: vec![],
+        };
+        let func_id = module
+            .declare_function(
+                &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
+                Linkage::Export,
+                &sig,
+            )
+            .unwrap();
+
+        let mut ctx = Context::new();
+        ctx.func.signature = sig;
+        let mut func_ctx = FunctionBuilderContext::new();
+        let mut bcx = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);
+
+        let block = bcx.create_block();
+        bcx.switch_to_block(block);
+        bcx.ins().return_(&[]);
+        bcx.seal_all_blocks();
+        bcx.finalize();
+
+        module.define_function(func_id, &mut ctx).unwrap();
+    }
 }
diff --git a/compiler/rustc_codegen_gcc/src/allocator.rs b/compiler/rustc_codegen_gcc/src/allocator.rs
index f4ebd42ee2d..cf8aa500c77 100644
--- a/compiler/rustc_codegen_gcc/src/allocator.rs
+++ b/compiler/rustc_codegen_gcc/src/allocator.rs
@@ -57,7 +57,7 @@ pub(crate) unsafe fn codegen(
             let from_name = mangle_internal_symbol(tcx, &global_fn_name(method.name));
             let to_name = mangle_internal_symbol(tcx, &default_fn_name(method.name));
 
-            create_wrapper_function(tcx, context, &from_name, &to_name, &types, output);
+            create_wrapper_function(tcx, context, &from_name, Some(&to_name), &types, output);
         }
     }
 
@@ -66,7 +66,7 @@ pub(crate) unsafe fn codegen(
         tcx,
         context,
         &mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
-        &mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind)),
+        Some(&mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind))),
         &[usize, usize],
         None,
     );
@@ -81,21 +81,21 @@ pub(crate) unsafe fn codegen(
     let value = context.new_rvalue_from_int(i8, value as i32);
     global.global_set_initializer_rvalue(value);
 
-    let name = mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE);
-    let global = context.new_global(None, GlobalKind::Exported, i8, name);
-    #[cfg(feature = "master")]
-    global.add_attribute(VarAttribute::Visibility(symbol_visibility_to_gcc(
-        tcx.sess.default_visibility(),
-    )));
-    let value = context.new_rvalue_from_int(i8, 0);
-    global.global_set_initializer_rvalue(value);
+    create_wrapper_function(
+        tcx,
+        context,
+        &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
+        None,
+        &[],
+        None,
+    );
 }
 
 fn create_wrapper_function(
     tcx: TyCtxt<'_>,
     context: &Context<'_>,
     from_name: &str,
-    to_name: &str,
+    to_name: Option<&str>,
     types: &[Type<'_>],
     output: Option<Type<'_>>,
 ) {
@@ -124,34 +124,40 @@ fn create_wrapper_function(
         // TODO(antoyo): emit unwind tables.
     }
 
-    let args: Vec<_> = types
-        .iter()
-        .enumerate()
-        .map(|(index, typ)| context.new_parameter(None, *typ, format!("param{}", index)))
-        .collect();
-    let callee = context.new_function(
-        None,
-        FunctionType::Extern,
-        output.unwrap_or(void),
-        &args,
-        to_name,
-        false,
-    );
-    #[cfg(feature = "master")]
-    callee.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
-
     let block = func.new_block("entry");
 
-    let args = args
-        .iter()
-        .enumerate()
-        .map(|(i, _)| func.get_param(i as i32).to_rvalue())
-        .collect::<Vec<_>>();
-    let ret = context.new_call(None, callee, &args);
-    //llvm::LLVMSetTailCall(ret, True);
-    if output.is_some() {
-        block.end_with_return(None, ret);
+    if let Some(to_name) = to_name {
+        let args: Vec<_> = types
+            .iter()
+            .enumerate()
+            .map(|(index, typ)| context.new_parameter(None, *typ, format!("param{}", index)))
+            .collect();
+        let callee = context.new_function(
+            None,
+            FunctionType::Extern,
+            output.unwrap_or(void),
+            &args,
+            to_name,
+            false,
+        );
+        #[cfg(feature = "master")]
+        callee.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
+
+        let args = args
+            .iter()
+            .enumerate()
+            .map(|(i, _)| func.get_param(i as i32).to_rvalue())
+            .collect::<Vec<_>>();
+        let ret = context.new_call(None, callee, &args);
+        //llvm::LLVMSetTailCall(ret, True);
+        if output.is_some() {
+            block.end_with_return(None, ret);
+        } else {
+            block.add_eval(None, ret);
+            block.end_with_void_return(None);
+        }
     } else {
+        assert!(output.is_none());
         block.end_with_void_return(None);
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/allocator.rs b/compiler/rustc_codegen_llvm/src/allocator.rs
index 4a78e694979..9dca63cfc8d 100644
--- a/compiler/rustc_codegen_llvm/src/allocator.rs
+++ b/compiler/rustc_codegen_llvm/src/allocator.rs
@@ -57,7 +57,7 @@ pub(crate) unsafe fn codegen(
             let from_name = mangle_internal_symbol(tcx, &global_fn_name(method.name));
             let to_name = mangle_internal_symbol(tcx, &default_fn_name(method.name));
 
-            create_wrapper_function(tcx, &cx, &from_name, &to_name, &args, output, false);
+            create_wrapper_function(tcx, &cx, &from_name, Some(&to_name), &args, output, false);
         }
     }
 
@@ -66,7 +66,7 @@ pub(crate) unsafe fn codegen(
         tcx,
         &cx,
         &mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
-        &mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind)),
+        Some(&mangle_internal_symbol(tcx, alloc_error_handler_name(alloc_error_handler_kind))),
         &[usize, usize], // size, align
         None,
         true,
@@ -81,11 +81,16 @@ pub(crate) unsafe fn codegen(
         let llval = llvm::LLVMConstInt(i8, val as u64, False);
         llvm::set_initializer(ll_g, llval);
 
-        let name = mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE);
-        let ll_g = cx.declare_global(&name, i8);
-        llvm::set_visibility(ll_g, llvm::Visibility::from_generic(tcx.sess.default_visibility()));
-        let llval = llvm::LLVMConstInt(i8, 0, False);
-        llvm::set_initializer(ll_g, llval);
+        // __rust_no_alloc_shim_is_unstable_v2
+        create_wrapper_function(
+            tcx,
+            &cx,
+            &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
+            None,
+            &[],
+            None,
+            false,
+        );
     }
 
     if tcx.sess.opts.debuginfo != DebugInfo::None {
@@ -99,7 +104,7 @@ fn create_wrapper_function(
     tcx: TyCtxt<'_>,
     cx: &SimpleCx<'_>,
     from_name: &str,
-    to_name: &str,
+    to_name: Option<&str>,
     args: &[&Type],
     output: Option<&Type>,
     no_return: bool,
@@ -128,33 +133,38 @@ fn create_wrapper_function(
         attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[uwtable]);
     }
 
-    let callee = declare_simple_fn(
-        &cx,
-        to_name,
-        llvm::CallConv::CCallConv,
-        llvm::UnnamedAddr::Global,
-        llvm::Visibility::Hidden,
-        ty,
-    );
-    if let Some(no_return) = no_return {
-        // -> ! DIFlagNoReturn
-        attributes::apply_to_llfn(callee, llvm::AttributePlace::Function, &[no_return]);
-    }
-    llvm::set_visibility(callee, llvm::Visibility::Hidden);
-
     let llbb = unsafe { llvm::LLVMAppendBasicBlockInContext(cx.llcx, llfn, c"entry".as_ptr()) };
-
     let mut bx = SBuilder::build(&cx, llbb);
-    let args = args
-        .iter()
-        .enumerate()
-        .map(|(i, _)| llvm::get_param(llfn, i as c_uint))
-        .collect::<Vec<_>>();
-    let ret = bx.call(ty, callee, &args, None);
-    llvm::LLVMSetTailCall(ret, True);
-    if output.is_some() {
-        bx.ret(ret);
+
+    if let Some(to_name) = to_name {
+        let callee = declare_simple_fn(
+            &cx,
+            to_name,
+            llvm::CallConv::CCallConv,
+            llvm::UnnamedAddr::Global,
+            llvm::Visibility::Hidden,
+            ty,
+        );
+        if let Some(no_return) = no_return {
+            // -> ! DIFlagNoReturn
+            attributes::apply_to_llfn(callee, llvm::AttributePlace::Function, &[no_return]);
+        }
+        llvm::set_visibility(callee, llvm::Visibility::Hidden);
+
+        let args = args
+            .iter()
+            .enumerate()
+            .map(|(i, _)| llvm::get_param(llfn, i as c_uint))
+            .collect::<Vec<_>>();
+        let ret = bx.call(ty, callee, &args, None);
+        llvm::LLVMSetTailCall(ret, True);
+        if output.is_some() {
+            bx.ret(ret);
+        } else {
+            bx.ret_void()
+        }
     } else {
+        assert!(output.is_none());
         bx.ret_void()
     }
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 92b9b6e132e..d0b6c7470fb 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -219,6 +219,7 @@ fn exported_symbols_provider_local<'tcx>(
             .chain([
                 mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
                 mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
+                mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
             ])
         {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
@@ -232,19 +233,6 @@ fn exported_symbols_provider_local<'tcx>(
                 },
             ));
         }
-
-        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(
-            tcx,
-            &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
-        ));
-        symbols.push((
-            exported_symbol,
-            SymbolExportInfo {
-                level: SymbolExportLevel::Rust,
-                kind: SymbolExportKind::Data,
-                used: false,
-            },
-        ))
     }
 
     if tcx.sess.instrument_coverage() || tcx.sess.opts.cg.profile_generate.enabled() {
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index 49a5e20d7cf..1db8ad72b32 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -85,10 +85,6 @@ pub fn mangle_internal_symbol<'tcx>(tcx: TyCtxt<'tcx>, item_name: &str) -> Strin
     if item_name == "rust_eh_personality" {
         // rust_eh_personality must not be renamed as LLVM hard-codes the name
         return "rust_eh_personality".to_owned();
-    } else if item_name == "__rust_no_alloc_shim_is_unstable" {
-        // Temporary back compat hack to give people the chance to migrate to
-        // include #[rustc_std_internal_symbol].
-        return "__rust_no_alloc_shim_is_unstable".to_owned();
     }
 
     let prefix = "_R";
diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index e1cc4ba25c4..b4176e9c1f4 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -31,8 +31,9 @@ unsafe extern "Rust" {
     #[rustc_std_internal_symbol]
     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
 
+    #[rustc_nounwind]
     #[rustc_std_internal_symbol]
-    static __rust_no_alloc_shim_is_unstable: u8;
+    fn __rust_no_alloc_shim_is_unstable_v2();
 }
 
 /// The global memory allocator.
@@ -88,7 +89,7 @@ pub unsafe fn alloc(layout: Layout) -> *mut u8 {
     unsafe {
         // Make sure we don't accidentally allow omitting the allocator shim in
         // stable code until it is actually stabilized.
-        core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
+        __rust_no_alloc_shim_is_unstable_v2();
 
         __rust_alloc(layout.size(), layout.align())
     }
@@ -171,7 +172,7 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
     unsafe {
         // Make sure we don't accidentally allow omitting the allocator shim in
         // stable code until it is actually stabilized.
-        core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
+        __rust_no_alloc_shim_is_unstable_v2();
 
         __rust_alloc_zeroed(layout.size(), layout.align())
     }
diff --git a/src/tools/miri/src/shims/extern_static.rs b/src/tools/miri/src/shims/extern_static.rs
index 2feed5a8352..a2ea3dbd88b 100644
--- a/src/tools/miri/src/shims/extern_static.rs
+++ b/src/tools/miri/src/shims/extern_static.rs
@@ -45,10 +45,6 @@ impl<'tcx> MiriMachine<'tcx> {
 
     /// Sets up the "extern statics" for this machine.
     pub fn init_extern_statics(ecx: &mut MiriInterpCx<'tcx>) -> InterpResult<'tcx> {
-        // "__rust_no_alloc_shim_is_unstable"
-        let val = ImmTy::from_int(0, ecx.machine.layouts.u8); // always 0, value does not matter
-        Self::alloc_extern_static(ecx, "__rust_no_alloc_shim_is_unstable", val)?;
-
         // "__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);
diff --git a/src/tools/miri/src/shims/foreign_items.rs b/src/tools/miri/src/shims/foreign_items.rs
index 39b930fdeb9..416cb1ab55e 100644
--- a/src/tools/miri/src/shims/foreign_items.rs
+++ b/src/tools/miri/src/shims/foreign_items.rs
@@ -611,6 +611,10 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     this.write_pointer(new_ptr, dest)
                 });
             }
+            name if name == this.mangle_internal_symbol("__rust_no_alloc_shim_is_unstable_v2") => {
+                // 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)?;
+            }
 
             // C memory handling functions
             "memcmp" => {
diff --git a/src/tools/miri/tests/pass/alloc-access-tracking.rs b/src/tools/miri/tests/pass/alloc-access-tracking.rs
index 0e88951dc43..9eba0ca171b 100644
--- a/src/tools/miri/tests/pass/alloc-access-tracking.rs
+++ b/src/tools/miri/tests/pass/alloc-access-tracking.rs
@@ -1,7 +1,7 @@
 #![no_std]
 #![no_main]
-//@compile-flags: -Zmiri-track-alloc-id=20 -Zmiri-track-alloc-accesses -Cpanic=abort
-//@normalize-stderr-test: "id 20" -> "id $$ALLOC"
+//@compile-flags: -Zmiri-track-alloc-id=19 -Zmiri-track-alloc-accesses -Cpanic=abort
+//@normalize-stderr-test: "id 19" -> "id $$ALLOC"
 //@only-target: linux # alloc IDs differ between OSes (due to extern static allocations)
 
 extern "Rust" {
diff --git a/tests/codegen/alloc-optimisation.rs b/tests/codegen/alloc-optimisation.rs
index 19f14647c1d..3735860d510 100644
--- a/tests/codegen/alloc-optimisation.rs
+++ b/tests/codegen/alloc-optimisation.rs
@@ -5,7 +5,8 @@
 pub fn alloc_test(data: u32) {
     // CHECK-LABEL: @alloc_test
     // CHECK-NEXT: start:
-    // CHECK-NEXT: {{.*}} load volatile i8, ptr @{{.*}}__rust_no_alloc_shim_is_unstable, align 1
+    // CHECK-NEXT: ; call __rustc::__rust_no_alloc_shim_is_unstable_v2
+    // CHECK-NEXT: tail call void @_R{{.+}}__rust_no_alloc_shim_is_unstable_v2()
     // CHECK-NEXT: ret void
     let x = Box::new(data);
     drop(x);
diff --git a/tests/codegen/unwind-landingpad-inline.rs b/tests/codegen/unwind-landingpad-inline.rs
index 920774b3402..1cf606279e6 100644
--- a/tests/codegen/unwind-landingpad-inline.rs
+++ b/tests/codegen/unwind-landingpad-inline.rs
@@ -10,8 +10,10 @@
 // See https://github.com/rust-lang/rust/issues/46515
 // CHECK-LABEL: @check_no_escape_in_landingpad
 // CHECK: start:
-// CHECK-NEXT: __rust_no_alloc_shim_is_unstable
-// CHECK-NEXT: __rust_no_alloc_shim_is_unstable
+// CHECK-NEXT: ; call __rustc::__rust_no_alloc_shim_is_unstable_v2
+// CHECK-NEXT: tail call void @[[NO_ALLOC_SHIM:_R.+__rust_no_alloc_shim_is_unstable_v2]]()
+// CHECK-NEXT: ; call __rustc::__rust_no_alloc_shim_is_unstable_v2
+// CHECK-NEXT: tail call void @[[NO_ALLOC_SHIM]]()
 // CHECK-NEXT: ret void
 #[no_mangle]
 pub fn check_no_escape_in_landingpad(f: fn()) {
diff --git a/tests/codegen/vec-iter-collect-len.rs b/tests/codegen/vec-iter-collect-len.rs
index a88573522d4..807548ef883 100644
--- a/tests/codegen/vec-iter-collect-len.rs
+++ b/tests/codegen/vec-iter-collect-len.rs
@@ -4,7 +4,9 @@
 #[no_mangle]
 pub fn get_len() -> usize {
     // CHECK-LABEL: @get_len
-    // CHECK-NOT: call
-    // CHECK-NOT: invoke
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ; call __rustc::__rust_no_alloc_shim_is_unstable_v2
+    // CHECK-NEXT: tail call void @_R{{.+}}__rust_no_alloc_shim_is_unstable_v2()
+    // CHECK-NEXT: ret i{{[0-9]+}} 3
     [1, 2, 3].iter().collect::<Vec<_>>().len()
 }
diff --git a/tests/codegen/vec-optimizes-away.rs b/tests/codegen/vec-optimizes-away.rs
index f6ed2898bda..93b55454b10 100644
--- a/tests/codegen/vec-optimizes-away.rs
+++ b/tests/codegen/vec-optimizes-away.rs
@@ -5,7 +5,8 @@
 pub fn sum_me() -> i32 {
     // CHECK-LABEL: @sum_me
     // CHECK-NEXT: {{^.*:$}}
-    // CHECK-NEXT: {{.*}} load volatile i8, ptr @{{.*}}__rust_no_alloc_shim_is_unstable, align 1
+    // CHECK-NEXT: ; call __rustc::__rust_no_alloc_shim_is_unstable_v2
+    // CHECK-NEXT: tail call void @_R{{.+}}__rust_no_alloc_shim_is_unstable_v2()
     // CHECK-NEXT: ret i32 6
     vec![1, 2, 3].iter().sum::<i32>()
 }
diff --git a/tests/run-make/no-alloc-shim/foo.rs b/tests/run-make/no-alloc-shim/foo.rs
index 42606961f8b..b5d0d394d2b 100644
--- a/tests/run-make/no-alloc-shim/foo.rs
+++ b/tests/run-make/no-alloc-shim/foo.rs
@@ -1,4 +1,4 @@
-#![feature(default_alloc_error_handler)]
+#![feature(rustc_attrs)]
 #![no_std]
 #![no_main]
 
@@ -31,8 +31,8 @@ unsafe impl GlobalAlloc for Alloc {
 }
 
 #[cfg(not(check_feature_gate))]
-#[no_mangle]
-static __rust_no_alloc_shim_is_unstable: u8 = 0;
+#[rustc_std_internal_symbol]
+fn __rust_no_alloc_shim_is_unstable_v2() {}
 
 #[no_mangle]
 extern "C" fn main(_argc: core::ffi::c_int, _argv: *const *const i8) -> i32 {
diff --git a/tests/run-make/no-alloc-shim/rmake.rs b/tests/run-make/no-alloc-shim/rmake.rs
index d61ef5de8c5..47cabfc208c 100644
--- a/tests/run-make/no-alloc-shim/rmake.rs
+++ b/tests/run-make/no-alloc-shim/rmake.rs
@@ -7,12 +7,6 @@
 //@ ignore-cross-compile
 // Reason: the compiled binary is executed
 
-//@ ignore-msvc
-//FIXME(Oneirical): Getting this to work on MSVC requires passing libcmt.lib to CC,
-// which is not trivial to do.
-// Tracking issue: https://github.com/rust-lang/rust/issues/128602
-// Discussion: https://github.com/rust-lang/rust/pull/128407#discussion_r1702439172
-
 use run_make_support::{cc, has_extension, has_prefix, run, rustc, shallow_find_files};
 
 fn main() {
@@ -30,15 +24,28 @@ fn main() {
         has_prefix(path, "libcompiler_builtins") && has_extension(path, "rlib")
     });
 
+    #[allow(unused_mut)]
+    let mut platform_args = Vec::<String>::new();
+    #[cfg(target_env = "msvc")]
+    {
+        platform_args.push("-MD".to_string());
+
+        // `/link` tells MSVC that the remaining arguments are linker options.
+        platform_args.push("/link".to_string());
+        platform_args.push("vcruntime.lib".to_string());
+        platform_args.push("msvcrt.lib".to_string());
+    }
+
     cc().input("foo.o")
         .out_exe("foo")
+        .args(&platform_args)
         .args(&alloc_libs)
         .args(&core_libs)
         .args(&compiler_builtins_libs)
         .run();
     run("foo");
 
-    // Check that linking without __rust_no_alloc_shim_is_unstable defined fails
+    // Check that linking without __rust_no_alloc_shim_is_unstable_v2 defined fails
     rustc()
         .input("foo.rs")
         .crate_type("bin")
@@ -48,6 +55,7 @@ fn main() {
         .run();
     cc().input("foo.o")
         .out_exe("foo")
+        .args(&platform_args)
         .args(&alloc_libs)
         .args(&core_libs)
         .args(&compiler_builtins_libs)
diff --git a/tests/run-make/symbols-all-mangled/rmake.rs b/tests/run-make/symbols-all-mangled/rmake.rs
index 79ddd06bb94..2cf57975800 100644
--- a/tests/run-make/symbols-all-mangled/rmake.rs
+++ b/tests/run-make/symbols-all-mangled/rmake.rs
@@ -35,10 +35,6 @@ fn symbols_check_archive(path: &str) {
             continue; // All compiler-builtins symbols must remain unmangled
         }
 
-        if name == "__rust_no_alloc_shim_is_unstable" {
-            continue; // FIXME remove exception once we mangle this symbol
-        }
-
         if name.contains("rust_eh_personality") {
             continue; // Unfortunately LLVM doesn't allow us to mangle this symbol
         }
@@ -75,10 +71,6 @@ fn symbols_check(path: &str) {
             continue;
         }
 
-        if name == "__rust_no_alloc_shim_is_unstable" {
-            continue; // FIXME remove exception once we mangle this symbol
-        }
-
         if name.contains("rust_eh_personality") {
             continue; // Unfortunately LLVM doesn't allow us to mangle this symbol
         }
diff --git a/tests/ui/sanitizer/dataflow-abilist.txt b/tests/ui/sanitizer/dataflow-abilist.txt
index fe04838f549..3d32397a175 100644
--- a/tests/ui/sanitizer/dataflow-abilist.txt
+++ b/tests/ui/sanitizer/dataflow-abilist.txt
@@ -503,3 +503,4 @@ fun:__rust_realloc=uninstrumented
 fun:_ZN4core*=uninstrumented
 fun:_ZN3std*=uninstrumented
 fun:rust_eh_personality=uninstrumented
+fun:_R*__rustc*=uninstrumented