rustc: Handle some libstd symbole exports better

src/liballoc_jemalloc/lib.rs

@@ -107,7 +107,7 @@ mod contents {
     // ABI
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_alloc(size: usize,
                                      align: usize,
                                      err: *mut u8) -> *mut u8 {
@@ -122,13 +122,13 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_oom(err: *const u8) -> ! {
         System.oom((*(err as *const AllocErr)).clone())
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_dealloc(ptr: *mut u8,
                                        size: usize,
                                        align: usize) {
@@ -137,7 +137,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_usable_size(layout: *const u8,
                                            min: *mut usize,
                                            max: *mut usize) {
@@ -153,7 +153,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_realloc(ptr: *mut u8,
                                        _old_size: usize,
                                        old_align: usize,
@@ -177,7 +177,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_alloc_zeroed(size: usize,
                                             align: usize,
                                             err: *mut u8) -> *mut u8 {
@@ -196,7 +196,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_alloc_excess(size: usize,
                                             align: usize,
                                             excess: *mut usize,
@@ -210,7 +210,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_realloc_excess(ptr: *mut u8,
                                               old_size: usize,
                                               old_align: usize,
@@ -227,7 +227,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_grow_in_place(ptr: *mut u8,
                                              old_size: usize,
                                              old_align: usize,
@@ -237,7 +237,7 @@ mod contents {
     }
 
     #[no_mangle]
-    #[linkage = "external"]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rde_shrink_in_place(ptr: *mut u8,
                                                _old_size: usize,
                                                old_align: usize,

src/librustc_allocator/expand.rs

@@ -177,9 +177,13 @@ impl<'a> AllocFnFactory<'a> {
 
         let no_mangle = Symbol::intern("no_mangle");
         let no_mangle = self.cx.meta_word(self.span, no_mangle);
+
+        let special = Symbol::intern("rustc_std_internal_symbol");
+        let special = self.cx.meta_word(self.span, special);
         vec![
             self.cx.attribute(self.span, linkage),
             self.cx.attribute(self.span, no_mangle),
+            self.cx.attribute(self.span, special),
         ]
     }
 

src/librustc_trans/back/symbol_export.rs

@@ -21,6 +21,7 @@ use rustc::ty::TyCtxt;
 use rustc::ty::maps::Providers;
 use rustc::util::nodemap::FxHashMap;
 use rustc_allocator::ALLOCATOR_METHODS;
+use syntax::attr;
 
 pub type ExportedSymbols = FxHashMap<
     CrateNum,
@@ -180,7 +181,15 @@ pub fn provide_extern(providers: &mut Providers) {
 }
 
 fn export_level(tcx: TyCtxt, sym_def_id: DefId) -> SymbolExportLevel {
-    if tcx.contains_extern_indicator(sym_def_id) {
+    // We export anything that's not mangled at the "C" layer as it probably has
+    // to do with ABI concerns. We do not, however, apply such treatment to
+    // special symbols in the standard library for various plumbing between
+    // core/std/allocators/etc. For example symbols used to hook up allocation
+    // are not considered for export
+    let is_extern = tcx.contains_extern_indicator(sym_def_id);
+    let std_internal = attr::contains_name(&tcx.get_attrs(sym_def_id),
+                                           "rustc_std_internal_symbol");
+    if is_extern && !std_internal {
         SymbolExportLevel::C
     } else {
         SymbolExportLevel::Rust

src/libstd/heap.rs

@@ -17,6 +17,7 @@ pub use alloc_system::System;
 
 #[cfg(not(test))]
 #[doc(hidden)]
+#[allow(unused_attributes)]
 pub mod __default_lib_allocator {
     use super::{System, Layout, Alloc, AllocErr};
     use ptr;
@@ -28,6 +29,7 @@ pub mod __default_lib_allocator {
     // ABI
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_alloc(size: usize,
                                      align: usize,
                                      err: *mut u8) -> *mut u8 {
@@ -42,18 +44,21 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_oom(err: *const u8) -> ! {
         System.oom((*(err as *const AllocErr)).clone())
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_dealloc(ptr: *mut u8,
                                        size: usize,
                                        align: usize) {
         System.dealloc(ptr, Layout::from_size_align_unchecked(size, align))
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_usable_size(layout: *const u8,
                                            min: *mut usize,
                                            max: *mut usize) {
@@ -63,6 +68,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_realloc(ptr: *mut u8,
                                        old_size: usize,
                                        old_align: usize,
@@ -81,6 +87,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_alloc_zeroed(size: usize,
                                             align: usize,
                                             err: *mut u8) -> *mut u8 {
@@ -95,6 +102,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_alloc_excess(size: usize,
                                             align: usize,
                                             excess: *mut usize,
@@ -113,6 +121,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_realloc_excess(ptr: *mut u8,
                                               old_size: usize,
                                               old_align: usize,
@@ -135,6 +144,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_grow_in_place(ptr: *mut u8,
                                              old_size: usize,
                                              old_align: usize,
@@ -149,6 +159,7 @@ pub mod __default_lib_allocator {
     }
 
     #[no_mangle]
+    #[rustc_std_internal_symbol]
     pub unsafe extern fn __rdl_shrink_in_place(ptr: *mut u8,
                                                old_size: usize,
                                                old_align: usize,

src/libsyntax/feature_gate.rs

@@ -917,6 +917,12 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                  "allow_fail attribute is currently unstable",
                                  cfg_fn!(allow_fail))),
 
+    ("rustc_std_internal_symbol", Whitelisted, Gated(Stability::Unstable,
+                                     "rustc_attrs",
+                                     "this is an internal attribute that will \
+                                      never be stable",
+                                     cfg_fn!(rustc_attrs))),
+
     // Crate level attributes
     ("crate_name", CrateLevel, Ungated),
     ("crate_type", CrateLevel, Ungated),

src/test/run-make/cdylib-fewer-symbols/Makefile

@@ -0,0 +1,17 @@
+# Test that allocator-related symbols don't show up as exported from a cdylib as
+# they're internal to Rust and not part of the public ABI.
+
+-include ../tools.mk
+
+ifdef IS_MSVC
+all:
+	true
+else
+all:
+	$(RUSTC) foo.rs
+	nm -g "$(call DYLIB,foo)"
+	nm -g "$(call DYLIB,foo)" | grep -vq __rdl_
+	nm -g "$(call DYLIB,foo)" | grep -vq __rde_
+	nm -g "$(call DYLIB,foo)" | grep -vq __rg_
+	nm -g "$(call DYLIB,foo)" | grep -vq __rust_
+endif

src/test/run-make/cdylib-fewer-symbols/foo.rs

@@ -0,0 +1,16 @@
+// Copyright 2017 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.
+
+#![crate_type = "cdylib"]
+
+#[no_mangle]
+pub extern fn foo() -> u32 {
+    3
+}