Limit symbols exported from proc macros

Only __rustc_proc_macro_decls_*__ and rust_metadata_* need to be
exported for proc macros to work. All other symbols only increase binary
size and have the potential to conflict with symbols from the host
compiler.

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -656,9 +656,7 @@ impl<'a> Linker for GccLinker<'a> {
             return;
         }
 
-        if crate_type == CrateType::ProcMacro {
-            return;
-        }
+        // FIXME hide #[no_mangle] symbols for proc-macros
 
         let is_windows = self.sess.target.is_like_windows;
         let path = tmpdir.join(if is_windows { "list.def" } else { "list" });

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -257,16 +257,18 @@ fn exported_symbols_provider_local<'tcx>(
         }));
     }
 
-    if tcx.sess.crate_types().contains(&CrateType::Dylib) {
+    if tcx.sess.crate_types().contains(&CrateType::Dylib)
+        || tcx.sess.crate_types().contains(&CrateType::ProcMacro)
+    {
         let symbol_name = metadata_symbol_name(tcx);
         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
         symbols.push((
             exported_symbol,
             SymbolExportInfo {
-                level: SymbolExportLevel::Rust,
+                level: SymbolExportLevel::C,
                 kind: SymbolExportKind::Data,
-                used: false,
+                used: true,
             },
         ));
     }

src/test/run-make-fulldeps/symbol-visibility/Makefile

@@ -5,6 +5,7 @@ include ../tools.mk
 NM=nm -D
 CDYLIB_NAME=liba_cdylib.so
 RDYLIB_NAME=liba_rust_dylib.so
+PROC_MACRO_NAME=liba_proc_macro.so
 EXE_NAME=an_executable
 COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.so
 
@@ -12,6 +13,7 @@ ifeq ($(UNAME),Darwin)
 NM=nm -gU
 CDYLIB_NAME=liba_cdylib.dylib
 RDYLIB_NAME=liba_rust_dylib.dylib
+PROC_MACRO_NAME=liba_proc_macro.dylib
 EXE_NAME=an_executable
 COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.dylib
 endif
@@ -20,6 +22,7 @@ ifdef IS_WINDOWS
 NM=nm -g
 CDYLIB_NAME=liba_cdylib.dll.a
 RDYLIB_NAME=liba_rust_dylib.dll.a
+PROC_MACRO_NAME=liba_proc_macro.dll
 EXE_NAME=an_executable.exe
 COMBINED_CDYLIB_NAME=libcombined_rlib_dylib.dll.a
 endif
@@ -31,6 +34,7 @@ all:
 	$(RUSTC) -Zshare-generics=no an_rlib.rs
 	$(RUSTC) -Zshare-generics=no a_cdylib.rs
 	$(RUSTC) -Zshare-generics=no a_rust_dylib.rs
+	$(RUSTC) -Zshare-generics=no a_proc_macro.rs
 	$(RUSTC) -Zshare-generics=no an_executable.rs
 	$(RUSTC) -Zshare-generics=no a_cdylib.rs --crate-name combined_rlib_dylib --crate-type=rlib,cdylib
 
@@ -54,6 +58,14 @@ all:
 	# Check that a Rust dylib does not export generics if -Zshare-generics=no
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_generic_function_from_rlib)" -eq "0" ]
 
+	# Check that a proc macro exports its public #[no_mangle] functions
+	# FIXME avoid exporting #[no_mangle] symbols for proc macros
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_cdylib)" -eq "1" ]
+	# Check that a proc macro exports the public #[no_mangle] functions of dependencies
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "1" ]
+	# Check that a proc macro DOES NOT export any public Rust functions
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c $(RE_ANY_RUST_SYMBOL))" -eq "0" ]
+
 # FIXME(nbdd0121): This is broken in MinGW, see https://github.com/rust-lang/rust/pull/95604#issuecomment-1101564032
 ifndef IS_WINDOWS
 	# Check that an executable does not export any dynamic symbols
@@ -75,6 +87,7 @@ endif
 	$(RUSTC) -Zshare-generics=yes an_rlib.rs
 	$(RUSTC) -Zshare-generics=yes a_cdylib.rs
 	$(RUSTC) -Zshare-generics=yes a_rust_dylib.rs
+	$(RUSTC) -Zshare-generics=yes a_proc_macro.rs
 	$(RUSTC) -Zshare-generics=yes an_executable.rs
 
 	# Check that a cdylib exports its public #[no_mangle] functions
@@ -94,6 +107,14 @@ endif
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_rust_function_from_rlib)" -eq "1" ]
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -v __imp_ | grep -c public_generic_function_from_rlib)" -eq "1" ]
 
+	# Check that a proc macro exports its public #[no_mangle] functions
+	# FIXME avoid exporting #[no_mangle] symbols for proc macros
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_cdylib)" -eq "1" ]
+	# Check that a proc macro exports the public #[no_mangle] functions of dependencies
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "1" ]
+	# Check that a proc macro DOES NOT export any public Rust functions
+	[ "$$($(NM) $(TMPDIR)/$(CDYLIB_NAME) | grep -v __imp_ | grep -c $(RE_ANY_RUST_SYMBOL))" -eq "0" ]
+
 ifndef IS_WINDOWS
 	# Check that an executable does not export any dynamic symbols
 	[ "$$($(NM) $(TMPDIR)/$(EXE_NAME) | grep -v __imp_ | grep -c public_c_function_from_rlib)" -eq "0" ]

src/test/run-make-fulldeps/symbol-visibility/a_proc_macro.rs

@@ -0,0 +1,9 @@
+#![crate_type = "proc-macro"]
+
+extern crate an_rlib;
+
+// This should not be exported
+#[no_mangle]
+extern "C" fn public_c_function_from_cdylib() {
+    an_rlib::public_c_function_from_rlib();
+}