rustc: Preserve reachable extern fns with LTO

src/librustc/metadata/common.rs

@@ -209,6 +209,9 @@ pub static tag_dylib_dependency_formats: uint = 0x67;
 pub static tag_method_argument_names: uint = 0x8e;
 pub static tag_method_argument_name: uint = 0x8f;
 
+pub static tag_reachable_extern_fns: uint = 0x90;
+pub static tag_reachable_extern_fn_id: uint = 0x91;
+
 #[deriving(Clone, Show)]
 pub struct LinkMeta {
     pub crateid: CrateId,

src/librustc/metadata/csearch.rs

@@ -314,3 +314,10 @@ pub fn get_method_arg_names(cstore: &cstore::CStore, did: ast::DefId)
     let cdata = cstore.get_crate_data(did.krate);
     decoder::get_method_arg_names(&*cdata, did.node)
 }
+
+pub fn get_reachable_extern_fns(cstore: &cstore::CStore, cnum: ast::CrateNum)
+    -> Vec<ast::DefId>
+{
+    let cdata = cstore.get_crate_data(cnum);
+    decoder::get_reachable_extern_fns(&*cdata)
+}

src/librustc/metadata/decoder.rs

@@ -1324,3 +1324,17 @@ pub fn get_method_arg_names(cdata: Cmd, id: ast::NodeId) -> Vec<String> {
     }
     return ret;
 }
+
+pub fn get_reachable_extern_fns(cdata: Cmd) -> Vec<ast::DefId> {
+    let mut ret = Vec::new();
+    let items = reader::get_doc(ebml::Doc::new(cdata.data()),
+                                tag_reachable_extern_fns);
+    reader::tagged_docs(items, tag_reachable_extern_fn_id, |doc| {
+        ret.push(ast::DefId {
+            krate: cdata.cnum,
+            node: reader::doc_as_u32(doc),
+        });
+        true
+    });
+    return ret;
+}

src/librustc/metadata/encoder.rs

@@ -75,6 +75,7 @@ pub struct EncodeParams<'a> {
     pub link_meta: &'a LinkMeta,
     pub cstore: &'a cstore::CStore,
     pub encode_inlined_item: EncodeInlinedItem<'a>,
+    pub reachable: &'a NodeSet,
 }
 
 pub struct EncodeContext<'a> {
@@ -87,6 +88,7 @@ pub struct EncodeContext<'a> {
     pub cstore: &'a cstore::CStore,
     pub encode_inlined_item: RefCell<EncodeInlinedItem<'a>>,
     pub type_abbrevs: tyencode::abbrev_map,
+    pub reachable: &'a NodeSet,
 }
 
 fn encode_name(ebml_w: &mut Encoder, name: Name) {
@@ -1700,6 +1702,26 @@ fn encode_misc_info(ecx: &EncodeContext,
     ebml_w.end_tag();
 }
 
+fn encode_reachable_extern_fns(ecx: &EncodeContext, ebml_w: &mut Encoder) {
+    ebml_w.start_tag(tag_reachable_extern_fns);
+
+    for id in ecx.reachable.iter() {
+        match ecx.tcx.map.find(*id) {
+            Some(ast_map::NodeItem(i)) => {
+                match i.node {
+                    ast::ItemFn(_, _, abi, _, _) if abi != abi::Rust => {
+                        ebml_w.wr_tagged_u32(tag_reachable_extern_fn_id, *id);
+                    }
+                    _ => {}
+                }
+            }
+            _ => {}
+        }
+    }
+
+    ebml_w.end_tag();
+}
+
 fn encode_crate_dep(ebml_w: &mut Encoder,
                     dep: decoder::CrateDep) {
     ebml_w.start_tag(tag_crate_dep);
@@ -1799,6 +1821,7 @@ fn encode_metadata_inner(wr: &mut MemWriter, parms: EncodeParams, krate: &Crate)
         encode_inlined_item,
         link_meta,
         non_inlineable_statics,
+        reachable,
         ..
     } = parms;
     let ecx = EncodeContext {
@@ -1811,6 +1834,7 @@ fn encode_metadata_inner(wr: &mut MemWriter, parms: EncodeParams, krate: &Crate)
         cstore: cstore,
         encode_inlined_item: RefCell::new(encode_inlined_item),
         type_abbrevs: RefCell::new(HashMap::new()),
+        reachable: reachable,
      };
 
     let mut ebml_w = writer::Encoder::new(wr);
@@ -1862,6 +1886,7 @@ fn encode_metadata_inner(wr: &mut MemWriter, parms: EncodeParams, krate: &Crate)
     // Encode miscellaneous info.
     i = ebml_w.writer.tell().unwrap();
     encode_misc_info(&ecx, krate, &mut ebml_w);
+    encode_reachable_extern_fns(&ecx, &mut ebml_w);
     stats.misc_bytes = ebml_w.writer.tell().unwrap() - i;
 
     // Encode and index the items.

src/librustc/middle/trans/base.rs

@@ -2194,6 +2194,7 @@ pub fn crate_ctxt_to_encode_parms<'r>(cx: &'r CrateContext, ie: encoder::EncodeI
             link_meta: &cx.link_meta,
             cstore: &cx.sess().cstore,
             encode_inlined_item: ie,
+            reachable: &cx.reachable,
         }
 }
 
@@ -2330,6 +2331,16 @@ pub fn trans_crate(krate: ast::Crate,
         ccx.item_symbols.borrow().find(id).map(|s| s.to_string())
     }).collect();
 
+    // For the purposes of LTO, we add to the reachable set all of the upstream
+    // reachable extern fns. These functions are all part of the public ABI of
+    // the final product, so LTO needs to preserve them.
+    ccx.sess().cstore.iter_crate_data(|cnum, _| {
+        let syms = csearch::get_reachable_extern_fns(&ccx.sess().cstore, cnum);
+        reachable.extend(syms.move_iter().map(|did| {
+            csearch::get_symbol(&ccx.sess().cstore, did)
+        }));
+    });
+
     // Make sure that some other crucial symbols are not eliminated from the
     // module. This includes the main function, the crate map (used for debug
     // log settings and I/O), and finally the curious rust_stack_exhausted

src/test/run-make/issue-14500/Makefile

@@ -0,0 +1,14 @@
+-include ../tools.mk
+
+# Test to make sure that reachable extern fns are always available in final
+# productcs, including when LTO is used. In this test, the `foo` crate has a
+# reahable symbol, and is a dependency of the `bar` crate. When the `bar` crate
+# is compiled with LTO, it shouldn't strip the symbol from `foo`, and that's the
+# only way that `foo.c` will successfully compile.
+
+all:
+	$(RUSTC) foo.rs --crate-type=rlib
+	$(RUSTC) bar.rs --crate-type=staticlib -Zlto -L. -o $(TMPDIR)/libbar.a
+	$(CC) foo.c -lbar -o $(call RUN_BINFILE,foo) $(EXTRACFLAGS)
+	$(call RUN,foo)
+

src/test/run-make/issue-14500/bar.rs

@@ -0,0 +1,11 @@
+// Copyright 2014 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.
+
+extern crate foo;

src/test/run-make/issue-14500/foo.c

@@ -0,0 +1,16 @@
+// Copyright 2014 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.
+
+extern void foo();
+
+int main() {
+    foo();
+    return 0;
+}

src/test/run-make/issue-14500/foo.rs

@@ -0,0 +1,12 @@
+// Copyright 2014 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.
+
+#[no_mangle]
+pub extern fn foo() {}

src/test/run-make/lto-smoke-c/Makefile

@@ -1,23 +1,10 @@
 -include ../tools.mk
 
-ifdef IS_WINDOWS
-	EXTRAFLAGS :=
-else
-ifeq ($(shell uname),Darwin)
-else
-ifeq ($(shell uname),FreeBSD)
-	EXTRAFLAGS := -lm -lpthread -lgcc_s
-else
-	EXTRAFLAGS := -lm -lrt -ldl -lpthread
-endif
-endif
-endif
-
 # Apparently older versions of GCC segfault if -g is passed...
 CC := $(CC:-g=)
 
 all:
 	$(RUSTC) foo.rs -Z lto
 	ln -s $(call STATICLIB,foo-*) $(call STATICLIB,foo)
-	$(CC) bar.c -lfoo -o $(call RUN_BINFILE,bar) $(EXTRAFLAGS) -lstdc++
+	$(CC) bar.c -lfoo -o $(call RUN_BINFILE,bar) $(EXTRACFLAGS) -lstdc++
 	$(call RUN,bar)

src/test/run-make/tools.mk

@@ -53,6 +53,20 @@ RPATH_LINK_SEARCH = -Wl,-rpath-link=$(1)
 endif
 endif
 
+# Extra flags needed to compile a working executable with the standard library
+ifdef IS_WINDOWS
+	EXTRACFLAGS :=
+else
+ifeq ($(shell uname),Darwin)
+else
+ifeq ($(shell uname),FreeBSD)
+	EXTRACFLAGS := -lm -lpthread -lgcc_s
+else
+	EXTRACFLAGS := -lm -lrt -ldl -lpthread
+endif
+endif
+endif
+
 REMOVE_DYLIBS     = rm $(TMPDIR)/$(call DYLIB_GLOB,$(1))
 REMOVE_RLIBS      = rm $(TMPDIR)/$(call RLIB_GLOB,$(1))