Rollup merge of #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: #35119

2 files changed, 67 insertions, 0 deletions

diff --git a/src/libsyntax_ext/global_asm.rs b/src/libsyntax_ext/global_asm.rs
new file mode 100644
index 00000000000..dc67e1c45f6
--- /dev/null
+++ b/src/libsyntax_ext/global_asm.rs
@@ -0,0 +1,65 @@
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/// Module-level assembly support.
+///
+/// The macro defined here allows you to specify "top-level",
+/// "file-scoped", or "module-level" assembly. These synonyms
+/// all correspond to LLVM's module-level inline assembly instruction.
+///
+/// For example, `global_asm!("some assembly here")` translates to
+/// LLVM's `module asm "some assembly here"`. All of LLVM's caveats
+/// therefore apply.
+
+use syntax::ast;
+use syntax::ext::base;
+use syntax::ext::base::*;
+use syntax::feature_gate;
+use syntax::ptr::P;
+use syntax::symbol::Symbol;
+use syntax_pos::Span;
+use syntax::tokenstream;
+
+use syntax::util::small_vector::SmallVector;
+
+pub const MACRO: &'static str = "global_asm";
+
+pub fn expand_global_asm<'cx>(cx: &'cx mut ExtCtxt,
+                              sp: Span,
+                              tts: &[tokenstream::TokenTree]) -> Box<base::MacResult + 'cx> {
+    if !cx.ecfg.enable_global_asm() {
+        feature_gate::emit_feature_err(&cx.parse_sess,
+                                       MACRO,
+                                       sp,
+                                       feature_gate::GateIssue::Language,
+                                       feature_gate::EXPLAIN_GLOBAL_ASM);
+        return DummyResult::any(sp);
+    }
+
+    let mut p = cx.new_parser_from_tts(tts);
+    let (asm, _) = match expr_to_string(cx,
+                                        panictry!(p.parse_expr()),
+                                        "inline assembly must be a string literal") {
+        Some((s, st)) => (s, st),
+        None => return DummyResult::any(sp),
+    };
+
+    MacEager::items(SmallVector::one(P(ast::Item {
+        ident: ast::Ident::with_empty_ctxt(Symbol::intern("")),
+        attrs: Vec::new(),
+        id: ast::DUMMY_NODE_ID,
+        node: ast::ItemKind::GlobalAsm(P(ast::GlobalAsm {
+            asm: asm,
+            ctxt: cx.backtrace(),
+        })),
+        vis: ast::Visibility::Inherited,
+        span: sp,
+    })))
+}
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index 1e9b112b6df..e35e79df585 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -38,6 +38,7 @@ mod concat_idents;
 mod env;
 mod format;
 mod format_foreign;
+mod global_asm;
 mod log_syntax;
 mod trace_macros;
 
@@ -99,6 +100,7 @@ pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
         module_path: expand_mod,
 
         asm: asm::expand_asm,
+        global_asm: global_asm::expand_global_asm,
         cfg: cfg::expand_cfg,
         concat: concat::expand_syntax_ext,
         concat_idents: concat_idents::expand_syntax_ext,