Rollup merge of rust-lang#40702 - mrhota:global_asm, r=nagisa

Implement global_asm!() (RFC 1548)

This is a first attempt. ~~One (potential) problem I haven't solved is how to handle multiple usages of `global_asm!` in a module/crate. It looks like `LLVMSetModuleInlineAsm` overwrites module asm, and `LLVMAppendModuleInlineAsm` is not provided in LLVM C headers 😦~~

I can provide more detail as needed, but honestly, there's not a lot going on here.

r? @eddyb

CC @Amanieu @jackpot51

Tracking issue: rust-lang#35119

Author: frewsxcv

src/doc/unstable-book/src/SUMMARY.md

@@ -81,6 +81,7 @@
 - [future_atomic_orderings](future-atomic-orderings.md)
 - [generic_param_attrs](generic-param-attrs.md)
 - [get_type_id](get-type-id.md)
+- [global_asm](global_asm.md)
 - [heap_api](heap-api.md)
 - [i128](i128.md)
 - [i128_type](i128-type.md)

src/doc/unstable-book/src/asm.md

@@ -189,3 +189,5 @@ constraints, etc.
 
 [llvm-docs]: http://llvm.org/docs/LangRef.html#inline-assembler-expressions
 
+If you need more power and don't mind losing some of the niceties of
+`asm!`, check out [global_asm](global_asm.html).

src/doc/unstable-book/src/global_asm.md

@@ -0,0 +1,78 @@
+# `global_asm`
+
+The tracking issue for this feature is: [#35119]
+
+[#35119]: https://github.com/rust-lang/rust/issues/35119
+
+------------------------
+
+The `global_asm!` macro allows the programmer to write arbitrary
+assembly outside the scope of a function body, passing it through
+`rustc` and `llvm` to the assembler. The macro is a no-frills
+interface to LLVM's concept of [module-level inline assembly]. That is,
+all caveats applicable to LLVM's module-level inline assembly apply
+to `global_asm!`.
+
+[module-level inline assembly]: http://llvm.org/docs/LangRef.html#module-level-inline-assembly
+
+`global_asm!` fills a role not currently satisfied by either `asm!`
+or `#[naked]` functions. The programmer has _all_ features of the
+assembler at their disposal. The linker will expect to resolve any
+symbols defined in the inline assembly, modulo any symbols marked as
+external. It also means syntax for directives and assembly follow the
+conventions of the assembler in your toolchain.
+
+A simple usage looks like this:
+
+```rust,ignore
+# #![feature(global_asm)]
+# you also need relevant target_arch cfgs
+global_asm!(include_str!("something_neato.s"));
+```
+
+And a more complicated usage looks like this:
+
+```rust,ignore
+# #![feature(global_asm)]
+# #![cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+
+pub mod sally {
+    global_asm!(r#"
+        .global foo
+      foo:
+        jmp baz
+    "#);
+
+    #[no_mangle]
+    pub unsafe extern "C" fn baz() {}
+}
+
+// the symbols `foo` and `bar` are global, no matter where
+// `global_asm!` was used.
+extern "C" {
+    fn foo();
+    fn bar();
+}
+
+pub mod harry {
+    global_asm!(r#"
+        .global bar
+      bar:
+        jmp quux
+    "#);
+
+    #[no_mangle]
+    pub unsafe extern "C" fn quux() {}
+}
+```
+
+You may use `global_asm!` multiple times, anywhere in your crate, in
+whatever way suits you. The effect is as if you concatenated all
+usages and placed the larger, single usage in the crate root.
+
+------------------------
+
+If you don't need quite as much power and flexibility as
+`global_asm!` provides, and you don't mind restricting your inline
+assembly to `fn` bodies only, you might try the [asm](asm.html)
+feature instead.

src/librustc/hir/def.rs

@@ -57,6 +57,8 @@ pub enum Def {
     // Macro namespace
     Macro(DefId, MacroKind),
 
+    GlobalAsm(DefId),
+
     // Both namespaces
     Err,
 }
@@ -144,7 +146,8 @@ impl Def {
             Def::Variant(id) | Def::VariantCtor(id, ..) | Def::Enum(id) | Def::TyAlias(id) |
             Def::AssociatedTy(id) | Def::TyParam(id) | Def::Struct(id) | Def::StructCtor(id, ..) |
             Def::Union(id) | Def::Trait(id) | Def::Method(id) | Def::Const(id) |
-            Def::AssociatedConst(id) | Def::Local(id) | Def::Upvar(id, ..) | Def::Macro(id, ..) => {
+            Def::AssociatedConst(id) | Def::Local(id) | Def::Upvar(id, ..) | Def::Macro(id, ..) |
+            Def::GlobalAsm(id) => {
                 id
             }
 
@@ -185,6 +188,7 @@ impl Def {
             Def::Label(..) => "label",
             Def::SelfTy(..) => "self type",
             Def::Macro(..) => "macro",
+            Def::GlobalAsm(..) => "global asm",
             Def::Err => "unresolved item",
         }
     }

src/librustc/hir/intravisit.rs

@@ -474,6 +474,9 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item) {
             visitor.visit_id(item.id);
             walk_list!(visitor, visit_foreign_item, &foreign_module.items);
         }
+        ItemGlobalAsm(_) => {
+            visitor.visit_id(item.id);
+        }
         ItemTy(ref typ, ref type_parameters) => {
             visitor.visit_id(item.id);
             visitor.visit_ty(typ);

src/librustc/hir/lowering.rs

@@ -645,6 +645,13 @@ impl<'a> LoweringContext<'a> {
         }
     }
 
+    fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
+        P(hir::GlobalAsm {
+            asm: ga.asm,
+            ctxt: ga.ctxt,
+        })
+    }
+
     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
         Spanned {
             node: hir::Variant_ {
@@ -1287,6 +1294,7 @@ impl<'a> LoweringContext<'a> {
             }
             ItemKind::Mod(ref m) => hir::ItemMod(self.lower_mod(m)),
             ItemKind::ForeignMod(ref nm) => hir::ItemForeignMod(self.lower_foreign_mod(nm)),
+            ItemKind::GlobalAsm(ref ga) => hir::ItemGlobalAsm(self.lower_global_asm(ga)),
             ItemKind::Ty(ref t, ref generics) => {
                 hir::ItemTy(self.lower_ty(t), self.lower_generics(generics))
             }

src/librustc/hir/map/def_collector.rs

@@ -120,6 +120,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
                 DefPathData::ValueNs(i.ident.name.as_str()),
             ItemKind::MacroDef(..) => DefPathData::MacroDef(i.ident.name.as_str()),
             ItemKind::Mac(..) => return self.visit_macro_invoc(i.id, false),
+            ItemKind::GlobalAsm(..) => DefPathData::Misc,
             ItemKind::Use(ref view_path) => {
                 match view_path.node {
                     ViewPathGlob(..) => {}

src/librustc/hir/map/mod.rs

@@ -1056,6 +1056,7 @@ fn node_id_to_string(map: &Map, id: NodeId, include_id: bool) -> String {
                 ItemFn(..) => "fn",
                 ItemMod(..) => "mod",
                 ItemForeignMod(..) => "foreign mod",
+                ItemGlobalAsm(..) => "global asm",
                 ItemTy(..) => "ty",
                 ItemEnum(..) => "enum",
                 ItemStruct(..) => "struct",

src/librustc/hir/mod.rs

@@ -1493,6 +1493,12 @@ pub struct ForeignMod {
     pub items: HirVec<ForeignItem>,
 }
 
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub struct GlobalAsm {
+    pub asm: Symbol,
+    pub ctxt: SyntaxContext
+}
+
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct EnumDef {
     pub variants: HirVec<Variant>,
@@ -1684,6 +1690,8 @@ pub enum Item_ {
     ItemMod(Mod),
     /// An external module
     ItemForeignMod(ForeignMod),
+    /// Module-level inline assembly (from global_asm!)
+    ItemGlobalAsm(P<GlobalAsm>),
     /// A type alias, e.g. `type Foo = Bar<u8>`
     ItemTy(P<Ty>, Generics),
     /// An enum definition, e.g. `enum Foo<A, B> {C<A>, D<B>}`
@@ -1718,6 +1726,7 @@ impl Item_ {
             ItemFn(..) => "function",
             ItemMod(..) => "module",
             ItemForeignMod(..) => "foreign module",
+            ItemGlobalAsm(..) => "global asm",
             ItemTy(..) => "type alias",
             ItemEnum(..) => "enum",
             ItemStruct(..) => "struct",

src/librustc/hir/print.rs

@@ -630,6 +630,11 @@ impl<'a> State<'a> {
                 self.print_foreign_mod(nmod, &item.attrs)?;
                 self.bclose(item.span)?;
             }
+            hir::ItemGlobalAsm(ref ga) => {
+                self.head(&visibility_qualified(&item.vis, "global asm"))?;
+                word(&mut self.s, &ga.asm.as_str())?;
+                self.end()?
+            }
             hir::ItemTy(ref ty, ref params) => {
                 self.ibox(indent_unit)?;
                 self.ibox(0)?;

src/librustc/middle/reachable.rs

@@ -267,7 +267,8 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
                     hir::ItemMod(..) | hir::ItemForeignMod(..) |
                     hir::ItemImpl(..) | hir::ItemTrait(..) |
                     hir::ItemStruct(..) | hir::ItemEnum(..) |
-                    hir::ItemUnion(..) | hir::ItemDefaultImpl(..) => {}
+                    hir::ItemUnion(..) | hir::ItemDefaultImpl(..) |
+                    hir::ItemGlobalAsm(..) => {}
                 }
             }
             hir_map::NodeTraitItem(trait_method) => {

src/librustc/middle/resolve_lifetime.rs

@@ -314,7 +314,8 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
             hir::ItemUse(..) |
             hir::ItemMod(..) |
             hir::ItemDefaultImpl(..) |
-            hir::ItemForeignMod(..) => {
+            hir::ItemForeignMod(..) |
+            hir::ItemGlobalAsm(..) => {
                 // These sorts of items have no lifetime parameters at all.
                 intravisit::walk_item(self, item);
             }

src/librustc_driver/test.rs

@@ -233,6 +233,7 @@ impl<'a, 'gcx, 'tcx> Env<'a, 'gcx, 'tcx> {
                 hir::ItemStatic(..) |
                 hir::ItemFn(..) |
                 hir::ItemForeignMod(..) |
+                hir::ItemGlobalAsm(..) |
                 hir::ItemTy(..) => None,
 
                 hir::ItemEnum(..) |

src/librustc_incremental/calculate_svh/svh_visitor.rs

@@ -354,6 +354,7 @@ enum SawItemComponent {
     SawItemFn(Unsafety, Constness, Abi),
     SawItemMod,
     SawItemForeignMod(Abi),
+    SawItemGlobalAsm,
     SawItemTy,
     SawItemEnum,
     SawItemStruct,
@@ -372,6 +373,7 @@ fn saw_item(node: &Item_) -> SawItemComponent {
         ItemFn(_, unsafety, constness, abi, _, _) => SawItemFn(unsafety, constness, abi),
         ItemMod(..) => SawItemMod,
         ItemForeignMod(ref fm) => SawItemForeignMod(fm.abi),
+        ItemGlobalAsm(..) => SawItemGlobalAsm,
         ItemTy(..) => SawItemTy,
         ItemEnum(..) => SawItemEnum,
         ItemStruct(..) => SawItemStruct,
@@ -920,7 +922,8 @@ impl<'a, 'hash, 'tcx> StrictVersionHashVisitor<'a, 'hash, 'tcx> {
             Def::AssociatedConst(..) |
             Def::Local(..) |
             Def::Upvar(..) |
-            Def::Macro(..) => {
+            Def::Macro(..) |
+            Def::GlobalAsm(..) => {
                 DefHash::SawDefId.hash(self.st);
                 self.hash_def_id(def.def_id());
             }

src/librustc_llvm/ffi.rs

@@ -507,6 +507,7 @@ extern "C" {
 
     /// See Module::setModuleInlineAsm.
     pub fn LLVMSetModuleInlineAsm(M: ModuleRef, Asm: *const c_char);
+    pub fn LLVMRustAppendModuleInlineAsm(M: ModuleRef, Asm: *const c_char);
 
     /// See llvm::LLVMTypeKind::getTypeID.
     pub fn LLVMRustGetTypeKind(Ty: TypeRef) -> TypeKind;

src/librustc_metadata/decoder.rs

@@ -429,6 +429,7 @@ impl<'tcx> EntryKind<'tcx> {
             EntryKind::Trait(_) => Def::Trait(did),
             EntryKind::Enum(..) => Def::Enum(did),
             EntryKind::MacroDef(_) => Def::Macro(did, MacroKind::Bang),
+            EntryKind::GlobalAsm => Def::GlobalAsm(did),
 
             EntryKind::ForeignMod |
             EntryKind::Impl(_) |

src/librustc_metadata/encoder.rs

@@ -655,6 +655,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 return self.encode_info_for_mod(FromId(item.id, (m, &item.attrs, &item.vis)));
             }
             hir::ItemForeignMod(_) => EntryKind::ForeignMod,
+            hir::ItemGlobalAsm(..) => EntryKind::GlobalAsm,
             hir::ItemTy(..) => EntryKind::Type,
             hir::ItemEnum(..) => EntryKind::Enum(get_repr_options(&tcx, def_id)),
             hir::ItemStruct(ref struct_def, _) => {
@@ -895,6 +896,7 @@ impl<'a, 'b, 'tcx> IndexBuilder<'a, 'b, 'tcx> {
             hir::ItemFn(..) |
             hir::ItemMod(..) |
             hir::ItemForeignMod(..) |
+            hir::ItemGlobalAsm(..) |
             hir::ItemExternCrate(..) |
             hir::ItemUse(..) |
             hir::ItemDefaultImpl(..) |

src/librustc_metadata/schema.rs

@@ -227,6 +227,7 @@ pub enum EntryKind<'tcx> {
     ForeignImmStatic,
     ForeignMutStatic,
     ForeignMod,
+    GlobalAsm,
     Type,
     Enum(ReprOptions),
     Field,

src/librustc_privacy/lib.rs

@@ -160,7 +160,10 @@ impl<'a, 'tcx> Visitor<'tcx> for EmbargoVisitor<'a, 'tcx> {
                 self.prev_level
             }
             // Other `pub` items inherit levels from parents
-            _ => {
+            hir::ItemConst(..) | hir::ItemEnum(..) | hir::ItemExternCrate(..) |
+            hir::ItemGlobalAsm(..) | hir::ItemFn(..) | hir::ItemMod(..) |
+            hir::ItemStatic(..) | hir::ItemStruct(..) | hir::ItemTrait(..) |
+            hir::ItemTy(..) | hir::ItemUnion(..) | hir::ItemUse(..) => {
                 if item.vis == hir::Public { self.prev_level } else { None }
             }
         };
@@ -212,7 +215,9 @@ impl<'a, 'tcx> Visitor<'tcx> for EmbargoVisitor<'a, 'tcx> {
                     }
                 }
             }
-            _ => {}
+            hir::ItemUse(..) | hir::ItemStatic(..) | hir::ItemConst(..) |
+            hir::ItemGlobalAsm(..) | hir::ItemTy(..) | hir::ItemMod(..) |
+            hir::ItemFn(..) | hir::ItemExternCrate(..) | hir::ItemDefaultImpl(..) => {}
         }
 
         // Mark all items in interfaces of reachable items as reachable
@@ -225,6 +230,8 @@ impl<'a, 'tcx> Visitor<'tcx> for EmbargoVisitor<'a, 'tcx> {
             hir::ItemUse(..) => {}
             // The interface is empty
             hir::ItemDefaultImpl(..) => {}
+            // The interface is empty
+            hir::ItemGlobalAsm(..) => {}
             // Visit everything
             hir::ItemConst(..) | hir::ItemStatic(..) |
             hir::ItemFn(..) | hir::ItemTy(..) => {
@@ -1092,6 +1099,8 @@ impl<'a, 'tcx> Visitor<'tcx> for PrivateItemsInPublicInterfacesVisitor<'a, 'tcx>
             hir::ItemMod(..) => {}
             // Checked in resolve
             hir::ItemUse(..) => {}
+            // No subitems
+            hir::ItemGlobalAsm(..) => {}
             // Subitems of these items have inherited publicity
             hir::ItemConst(..) | hir::ItemStatic(..) | hir::ItemFn(..) |
             hir::ItemTy(..) => {

src/librustc_resolve/build_reduced_graph.rs

@@ -268,6 +268,8 @@ impl<'a> Resolver<'a> {
                 self.define(parent, ident, TypeNS, imported_binding);
             }
 
+            ItemKind::GlobalAsm(..) => {}
+
             ItemKind::Mod(..) if item.ident == keywords::Invalid.ident() => {} // Crate root
 
             ItemKind::Mod(..) => {

src/librustc_resolve/lib.rs

@@ -1707,7 +1707,7 @@ impl<'a> Resolver<'a> {
                 }
             }
 
-            ItemKind::ExternCrate(_) | ItemKind::MacroDef(..) => {
+            ItemKind::ExternCrate(_) | ItemKind::MacroDef(..) | ItemKind::GlobalAsm(_)=> {
                 // do nothing, these are just around to be encoded
             }
 

src/librustc_save_analysis/dump_visitor.rs

@@ -341,6 +341,7 @@ impl<'l, 'tcx: 'l, 'll, D: Dump + 'll> DumpVisitor<'l, 'tcx, 'll, D> {
             Def::AssociatedTy(..) |
             Def::AssociatedConst(..) |
             Def::PrimTy(_) |
+            Def::GlobalAsm(_) |
             Def::Err => {
                span_bug!(span,
                          "process_def_kind for unexpected item: {:?}",

src/librustc_save_analysis/lib.rs

@@ -701,6 +701,7 @@ impl<'l, 'tcx: 'l> SaveContext<'l, 'tcx> {
             Def::SelfTy(..) |
             Def::Label(..) |
             Def::Macro(..) |
+            Def::GlobalAsm(..) |
             Def::Err => None,
         }
     }

src/librustc_trans/asm.rs

@@ -124,3 +124,11 @@ pub fn trans_inline_asm<'a, 'tcx>(
             llvm::LLVMMDNodeInContext(bcx.ccx.llcx(), &val, 1));
     }
 }
+
+pub fn trans_global_asm<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
+                                  ga: &hir::GlobalAsm) {
+    let asm = CString::new(ga.asm.as_str().as_bytes()).unwrap();
+    unsafe {
+        llvm::LLVMRustAppendModuleInlineAsm(ccx.llmod(), asm.as_ptr());
+    }
+}