Auto merge of #108089 - Zoxc:windows-tls, r=bjorn3

Support TLS access into dylibs on Windows

This allows access to `#[thread_local]`  in upstream dylibs on Windows by introducing a MIR shim to return the address of the thread local. Accesses that go into an upstream dylib will call the MIR shim to get the address of it.

`convert_tls_rvalues` is introduced in `rustc_codegen_ssa` which rewrites MIR TLS accesses to dummy calls which are replaced with calls to the MIR shims when the dummy calls are lowered to backend calls.

A new `dll_tls_export` target option enables this behavior with a `false` value which is set for Windows platforms.

This fixes #84933.

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -54,12 +54,22 @@ pub(crate) fn codegen_tls_ref<'tcx>(
     def_id: DefId,
     layout: TyAndLayout<'tcx>,
 ) -> CValue<'tcx> {
-    let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
-    let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
-    if fx.clif_comments.enabled() {
-        fx.add_comment(local_data_id, format!("tls {:?}", def_id));
-    }
-    let tls_ptr = fx.bcx.ins().tls_value(fx.pointer_type, local_data_id);
+    let tls_ptr = if !def_id.is_local() && fx.tcx.needs_thread_local_shim(def_id) {
+        let instance = ty::Instance {
+            def: ty::InstanceDef::ThreadLocalShim(def_id),
+            substs: ty::InternalSubsts::empty(),
+        };
+        let func_ref = fx.get_function_ref(instance);
+        let call = fx.bcx.ins().call(func_ref, &[]);
+        fx.bcx.func.dfg.first_result(call)
+    } else {
+        let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
+        let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
+        if fx.clif_comments.enabled() {
+            fx.add_comment(local_data_id, format!("tls {:?}", def_id));
+        }
+        fx.bcx.ins().tls_value(fx.pointer_type, local_data_id)
+    };
     CValue::by_val(tls_ptr, layout)
 }
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -177,14 +177,29 @@ fn exported_symbols_provider_local(
 
     // FIXME: Sorting this is unnecessary since we are sorting later anyway.
     //        Can we skip the later sorting?
-    let mut symbols: Vec<_> = tcx.with_stable_hashing_context(|hcx| {
-        tcx.reachable_non_generics(LOCAL_CRATE)
-            .to_sorted(&hcx, true)
-            .into_iter()
-            .map(|(&def_id, &info)| (ExportedSymbol::NonGeneric(def_id), info))
-            .collect()
+    let sorted = tcx.with_stable_hashing_context(|hcx| {
+        tcx.reachable_non_generics(LOCAL_CRATE).to_sorted(&hcx, true)
     });
 
+    let mut symbols: Vec<_> =
+        sorted.iter().map(|(&def_id, &info)| (ExportedSymbol::NonGeneric(def_id), info)).collect();
+
+    // Export TLS shims
+    if !tcx.sess.target.dll_tls_export {
+        symbols.extend(sorted.iter().filter_map(|(&def_id, &info)| {
+            tcx.needs_thread_local_shim(def_id).then(|| {
+                (
+                    ExportedSymbol::ThreadLocalShim(def_id),
+                    SymbolExportInfo {
+                        level: info.level,
+                        kind: SymbolExportKind::Text,
+                        used: info.used,
+                    },
+                )
+            })
+        }))
+    }
+
     if tcx.entry_fn(()).is_some() {
         let exported_symbol =
             ExportedSymbol::NoDefId(SymbolName::new(tcx, tcx.sess.target.entry_name.as_ref()));
@@ -380,7 +395,9 @@ fn upstream_monomorphizations_provider(
                         continue;
                     }
                 }
-                ExportedSymbol::NonGeneric(..) | ExportedSymbol::NoDefId(..) => {
+                ExportedSymbol::NonGeneric(..)
+                | ExportedSymbol::ThreadLocalShim(..)
+                | ExportedSymbol::NoDefId(..) => {
                     // These are no monomorphizations
                     continue;
                 }
@@ -500,6 +517,16 @@ pub fn symbol_name_for_instance_in_crate<'tcx>(
                 instantiating_crate,
             )
         }
+        ExportedSymbol::ThreadLocalShim(def_id) => {
+            rustc_symbol_mangling::symbol_name_for_instance_in_crate(
+                tcx,
+                ty::Instance {
+                    def: ty::InstanceDef::ThreadLocalShim(def_id),
+                    substs: ty::InternalSubsts::empty(),
+                },
+                instantiating_crate,
+            )
+        }
         ExportedSymbol::DropGlue(ty) => rustc_symbol_mangling::symbol_name_for_instance_in_crate(
             tcx,
             Instance::resolve_drop_in_place(tcx, ty),
@@ -548,6 +575,8 @@ pub fn linking_symbol_name_for_instance_in_crate<'tcx>(
         ExportedSymbol::DropGlue(..) => None,
         // NoDefId always follow the target's default symbol decoration scheme.
         ExportedSymbol::NoDefId(..) => None,
+        // ThreadLocalShim always follow the target's default symbol decoration scheme.
+        ExportedSymbol::ThreadLocalShim(..) => None,
     };
 
     let (conv, args) = instance

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -516,8 +516,20 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
             mir::Rvalue::ThreadLocalRef(def_id) => {
                 assert!(bx.cx().tcx().is_static(def_id));
-                let static_ = bx.get_static(def_id);
                 let layout = bx.layout_of(bx.cx().tcx().static_ptr_ty(def_id));
+                let static_ = if !def_id.is_local() && bx.cx().tcx().needs_thread_local_shim(def_id)
+                {
+                    let instance = ty::Instance {
+                        def: ty::InstanceDef::ThreadLocalShim(def_id),
+                        substs: ty::InternalSubsts::empty(),
+                    };
+                    let fn_ptr = bx.get_fn_addr(instance);
+                    let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
+                    let fn_ty = bx.fn_decl_backend_type(&fn_abi);
+                    bx.call(fn_ty, Some(fn_abi), fn_ptr, &[], None)
+                } else {
+                    bx.get_static(def_id)
+                };
                 OperandRef { val: OperandValue::Immediate(static_), layout }
             }
             mir::Rvalue::Use(ref operand) => self.codegen_operand(bx, operand),

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -383,6 +383,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | ty::InstanceDef::DropGlue(..)
             | ty::InstanceDef::CloneShim(..)
             | ty::InstanceDef::FnPtrAddrShim(..)
+            | ty::InstanceDef::ThreadLocalShim(..)
             | ty::InstanceDef::Item(_) => {
                 // We need MIR for this fn
                 let Some((body, instance)) =

compiler/rustc_middle/src/middle/exported_symbols.rs

@@ -43,6 +43,7 @@ pub enum ExportedSymbol<'tcx> {
     NonGeneric(DefId),
     Generic(DefId, SubstsRef<'tcx>),
     DropGlue(Ty<'tcx>),
+    ThreadLocalShim(DefId),
     NoDefId(ty::SymbolName<'tcx>),
 }
 
@@ -58,6 +59,10 @@ impl<'tcx> ExportedSymbol<'tcx> {
             ExportedSymbol::DropGlue(ty) => {
                 tcx.symbol_name(ty::Instance::resolve_drop_in_place(tcx, ty))
             }
+            ExportedSymbol::ThreadLocalShim(def_id) => tcx.symbol_name(ty::Instance {
+                def: ty::InstanceDef::ThreadLocalShim(def_id),
+                substs: ty::InternalSubsts::empty(),
+            }),
             ExportedSymbol::NoDefId(symbol_name) => symbol_name,
         }
     }

compiler/rustc_middle/src/mir/mono.rs

@@ -382,6 +382,7 @@ impl<'tcx> CodegenUnit<'tcx> {
                             | InstanceDef::ClosureOnceShim { .. }
                             | InstanceDef::DropGlue(..)
                             | InstanceDef::CloneShim(..)
+                            | InstanceDef::ThreadLocalShim(..)
                             | InstanceDef::FnPtrAddrShim(..) => None,
                         }
                     }

compiler/rustc_middle/src/mir/tcx.rs

@@ -164,17 +164,7 @@ impl<'tcx> Rvalue<'tcx> {
             Rvalue::Repeat(ref operand, count) => {
                 tcx.mk_array_with_const_len(operand.ty(local_decls, tcx), count)
             }
-            Rvalue::ThreadLocalRef(did) => {
-                let static_ty = tcx.type_of(did).subst_identity();
-                if tcx.is_mutable_static(did) {
-                    tcx.mk_mut_ptr(static_ty)
-                } else if tcx.is_foreign_item(did) {
-                    tcx.mk_imm_ptr(static_ty)
-                } else {
-                    // FIXME: These things don't *really* have 'static lifetime.
-                    tcx.mk_imm_ref(tcx.lifetimes.re_static, static_ty)
-                }
-            }
+            Rvalue::ThreadLocalRef(did) => tcx.thread_local_ptr_ty(did),
             Rvalue::Ref(reg, bk, ref place) => {
                 let place_ty = place.ty(local_decls, tcx).ty;
                 tcx.mk_ref(reg, ty::TypeAndMut { ty: place_ty, mutbl: bk.to_mutbl_lossy() })

compiler/rustc_middle/src/mir/visit.rs

@@ -335,6 +335,7 @@ macro_rules! make_mir_visitor {
                         ty::InstanceDef::VTableShim(_def_id) |
                         ty::InstanceDef::ReifyShim(_def_id) |
                         ty::InstanceDef::Virtual(_def_id, _) |
+                        ty::InstanceDef::ThreadLocalShim(_def_id) |
                         ty::InstanceDef::ClosureOnceShim { call_once: _def_id, track_caller: _ } |
                         ty::InstanceDef::DropGlue(_def_id, None) => {}
 

compiler/rustc_middle/src/ty/instance.rs

@@ -82,6 +82,11 @@ pub enum InstanceDef<'tcx> {
     /// The `DefId` is the ID of the `call_once` method in `FnOnce`.
     ClosureOnceShim { call_once: DefId, track_caller: bool },
 
+    /// Compiler-generated accessor for thread locals which returns a reference to the thread local
+    /// the `DefId` defines. This is used to export thread locals from dylibs on platforms lacking
+    /// native support.
+    ThreadLocalShim(DefId),
+
     /// `core::ptr::drop_in_place::<T>`.
     ///
     /// The `DefId` is for `core::ptr::drop_in_place`.
@@ -156,6 +161,7 @@ impl<'tcx> InstanceDef<'tcx> {
             | InstanceDef::FnPtrShim(def_id, _)
             | InstanceDef::Virtual(def_id, _)
             | InstanceDef::Intrinsic(def_id)
+            | InstanceDef::ThreadLocalShim(def_id)
             | InstanceDef::ClosureOnceShim { call_once: def_id, track_caller: _ }
             | InstanceDef::DropGlue(def_id, _)
             | InstanceDef::CloneShim(def_id, _)
@@ -167,7 +173,9 @@ impl<'tcx> InstanceDef<'tcx> {
     pub fn def_id_if_not_guaranteed_local_codegen(self) -> Option<DefId> {
         match self {
             ty::InstanceDef::Item(def) => Some(def.did),
-            ty::InstanceDef::DropGlue(def_id, Some(_)) => Some(def_id),
+            ty::InstanceDef::DropGlue(def_id, Some(_)) | InstanceDef::ThreadLocalShim(def_id) => {
+                Some(def_id)
+            }
             InstanceDef::VTableShim(..)
             | InstanceDef::ReifyShim(..)
             | InstanceDef::FnPtrShim(..)
@@ -192,6 +200,7 @@ impl<'tcx> InstanceDef<'tcx> {
             | InstanceDef::ClosureOnceShim { call_once: def_id, track_caller: _ }
             | InstanceDef::DropGlue(def_id, _)
             | InstanceDef::CloneShim(def_id, _)
+            | InstanceDef::ThreadLocalShim(def_id)
             | InstanceDef::FnPtrAddrShim(def_id, _) => ty::WithOptConstParam::unknown(def_id),
         }
     }
@@ -215,6 +224,7 @@ impl<'tcx> InstanceDef<'tcx> {
         let def_id = match *self {
             ty::InstanceDef::Item(def) => def.did,
             ty::InstanceDef::DropGlue(_, Some(_)) => return false,
+            ty::InstanceDef::ThreadLocalShim(_) => return false,
             _ => return true,
         };
         matches!(
@@ -255,6 +265,9 @@ impl<'tcx> InstanceDef<'tcx> {
                 )
             });
         }
+        if let ty::InstanceDef::ThreadLocalShim(..) = *self {
+            return false;
+        }
         tcx.codegen_fn_attrs(self.def_id()).requests_inline()
     }
 
@@ -278,6 +291,7 @@ impl<'tcx> InstanceDef<'tcx> {
     pub fn has_polymorphic_mir_body(&self) -> bool {
         match *self {
             InstanceDef::CloneShim(..)
+            | InstanceDef::ThreadLocalShim(..)
             | InstanceDef::FnPtrAddrShim(..)
             | InstanceDef::FnPtrShim(..)
             | InstanceDef::DropGlue(_, Some(_)) => false,
@@ -310,6 +324,7 @@ fn fmt_instance(
         InstanceDef::Item(_) => Ok(()),
         InstanceDef::VTableShim(_) => write!(f, " - shim(vtable)"),
         InstanceDef::ReifyShim(_) => write!(f, " - shim(reify)"),
+        InstanceDef::ThreadLocalShim(_) => write!(f, " - shim(tls)"),
         InstanceDef::Intrinsic(_) => write!(f, " - intrinsic"),
         InstanceDef::Virtual(_, num) => write!(f, " - virtual#{}", num),
         InstanceDef::FnPtrShim(_, ty) => write!(f, " - shim({})", ty),

compiler/rustc_middle/src/ty/mod.rs

@@ -2386,6 +2386,7 @@ impl<'tcx> TyCtxt<'tcx> {
             | ty::InstanceDef::ClosureOnceShim { .. }
             | ty::InstanceDef::DropGlue(..)
             | ty::InstanceDef::CloneShim(..)
+            | ty::InstanceDef::ThreadLocalShim(..)
             | ty::InstanceDef::FnPtrAddrShim(..) => self.mir_shims(instance),
         }
     }

compiler/rustc_middle/src/ty/util.rs

@@ -597,6 +597,28 @@ impl<'tcx> TyCtxt<'tcx> {
         self.static_mutability(def_id) == Some(hir::Mutability::Mut)
     }
 
+    /// Returns `true` if the item pointed to by `def_id` is a thread local which needs a
+    /// thread local shim generated.
+    #[inline]
+    pub fn needs_thread_local_shim(self, def_id: DefId) -> bool {
+        !self.sess.target.dll_tls_export
+            && self.is_thread_local_static(def_id)
+            && !self.is_foreign_item(def_id)
+    }
+
+    /// Returns the type a reference to the thread local takes in MIR.
+    pub fn thread_local_ptr_ty(self, def_id: DefId) -> Ty<'tcx> {
+        let static_ty = self.type_of(def_id).subst_identity();
+        if self.is_mutable_static(def_id) {
+            self.mk_mut_ptr(static_ty)
+        } else if self.is_foreign_item(def_id) {
+            self.mk_imm_ptr(static_ty)
+        } else {
+            // FIXME: These things don't *really* have 'static lifetime.
+            self.mk_imm_ref(self.lifetimes.re_static, static_ty)
+        }
+    }
+
     /// Get the type of the pointer to the static that we use in MIR.
     pub fn static_ptr_ty(self, def_id: DefId) -> Ty<'tcx> {
         // Make sure that any constants in the static's type are evaluated.

compiler/rustc_mir_transform/src/inline.rs

@@ -271,6 +271,7 @@ impl<'tcx> Inliner<'tcx> {
             | InstanceDef::ClosureOnceShim { .. }
             | InstanceDef::DropGlue(..)
             | InstanceDef::CloneShim(..)
+            | InstanceDef::ThreadLocalShim(..)
             | InstanceDef::FnPtrAddrShim(..) => return Ok(()),
         }
 

compiler/rustc_mir_transform/src/inline/cycle.rs

@@ -83,6 +83,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
                 | InstanceDef::ReifyShim(_)
                 | InstanceDef::FnPtrShim(..)
                 | InstanceDef::ClosureOnceShim { .. }
+                | InstanceDef::ThreadLocalShim { .. }
                 | InstanceDef::CloneShim(..) => {}
 
                 // This shim does not call any other functions, thus there can be no recursion.

compiler/rustc_mir_transform/src/shim.rs

@@ -76,6 +76,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
 
             build_drop_shim(tcx, def_id, ty)
         }
+        ty::InstanceDef::ThreadLocalShim(..) => build_thread_local_shim(tcx, instance),
         ty::InstanceDef::CloneShim(def_id, ty) => build_clone_shim(tcx, def_id, ty),
         ty::InstanceDef::FnPtrAddrShim(def_id, ty) => build_fn_ptr_addr_shim(tcx, def_id, ty),
         ty::InstanceDef::Virtual(..) => {
@@ -322,6 +323,34 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
     }
 }
 
+fn build_thread_local_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'tcx> {
+    let def_id = instance.def_id();
+
+    let span = tcx.def_span(def_id);
+    let source_info = SourceInfo::outermost(span);
+
+    let mut blocks = IndexVec::with_capacity(1);
+    blocks.push(BasicBlockData {
+        statements: vec![Statement {
+            source_info,
+            kind: StatementKind::Assign(Box::new((
+                Place::return_place(),
+                Rvalue::ThreadLocalRef(def_id),
+            ))),
+        }],
+        terminator: Some(Terminator { source_info, kind: TerminatorKind::Return }),
+        is_cleanup: false,
+    });
+
+    new_body(
+        MirSource::from_instance(instance),
+        blocks,
+        IndexVec::from_raw(vec![LocalDecl::new(tcx.thread_local_ptr_ty(def_id), span)]),
+        0,
+        span,
+    )
+}
+
 /// Builds a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
 fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
     debug!("build_clone_shim(def_id={:?})", def_id);