Add support for parsing #[link_ordinal] attribute.

Author: crlf0710

src/librustc/hir/mod.rs

@@ -2626,6 +2626,11 @@ pub struct CodegenFnAttrs {
     /// probably isn't set when this is set, this is for foreign items while
     /// `#[export_name]` is for Rust-defined functions.
     pub link_name: Option<Symbol>,
+    /// The `#[link_ordinal = "..."]` attribute, indicating an ordinal an
+    /// imported function has in the dynamic library. Note that this must not
+    /// be set when `link_name` is set. This is for foreign items with the
+    /// "raw-dylib" kind.
+    pub link_ordinal: Option<usize>,
     /// The `#[target_feature(enable = "...")]` attribute and the enabled
     /// features (only enabled features are supported right now).
     pub target_features: Vec<Symbol>,
@@ -2685,6 +2690,7 @@ impl CodegenFnAttrs {
             optimize: OptimizeAttr::None,
             export_name: None,
             link_name: None,
+            link_ordinal: None,
             target_features: vec![],
             linkage: None,
             link_section: None,

src/librustc_typeck/collect.rs

@@ -2603,6 +2603,35 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
             }
         } else if attr.check_name(sym::link_name) {
             codegen_fn_attrs.link_name = attr.value_str();
+        } else if attr.check_name(sym::link_ordinal) {
+            use syntax::ast::{Lit, LitIntType, LitKind};
+            let meta_item_list = attr.meta_item_list();
+            let sole_meta_lit = if let Some(meta_item_list) = &meta_item_list {
+                if meta_item_list.len() == 1 {
+                    meta_item_list.get(0).and_then(|item| item.literal())
+                } else {
+                    None
+                }
+            } else {
+                None
+            };
+            if let Some(Lit { node: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) =
+                sole_meta_lit
+            {
+                if *ordinal <= std::usize::MAX as u128 {
+                    codegen_fn_attrs.link_ordinal = Some(*ordinal as usize);
+                } else {
+                    let msg = format!(
+                        "too large ordinal value in link_ordinal \
+                         value: `{}`",
+                        &ordinal
+                    );
+                    tcx.sess.span_err(attr.span, &msg);
+                }
+            } else {
+                let msg = "illegal ordinal format in link_ordinal";
+                tcx.sess.span_err(attr.span, &msg);
+            }
         }
     }
 
@@ -2704,6 +2733,15 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         codegen_fn_attrs.export_name = Some(name);
         codegen_fn_attrs.link_name = Some(name);
     }
+    if codegen_fn_attrs.link_name.is_some() && codegen_fn_attrs.link_ordinal.is_some() {
+        if let Some(span) = inline_span {
+            tcx.sess.span_err(
+                span,
+                "cannot use `#[link_name]` with \
+                 `#[link_ordinal]`",
+            );
+        }
+    }
 
     // Internal symbols to the standard library all have no_mangle semantics in
     // that they have defined symbol names present in the function name. This