rustc: Add _imp_ symbols later in compilation

src/librustc_trans/back/write.rs

@@ -12,6 +12,8 @@ use back::lto;
 use back::link::{self, get_linker, remove};
 use back::linker::LinkerInfo;
 use back::symbol_export::ExportedSymbols;
+use base;
+use consts;
 use rustc_incremental::{save_trans_partition, in_incr_comp_dir};
 use rustc::dep_graph::DepGraph;
 use rustc::middle::cstore::{LinkMeta, EncodedMetadata};
@@ -35,12 +37,13 @@ use syntax::attr;
 use syntax::ext::hygiene::Mark;
 use syntax_pos::MultiSpan;
 use syntax_pos::symbol::Symbol;
+use type_::Type;
 use context::{is_pie_binary, get_reloc_model};
 use jobserver::{Client, Acquired};
 use rustc_demangle;
 
 use std::any::Any;
-use std::ffi::CString;
+use std::ffi::{CString, CStr};
 use std::fs;
 use std::io;
 use std::io::Write;
@@ -315,6 +318,8 @@ pub struct CodegenContext {
     metadata_module_config: Arc<ModuleConfig>,
     allocator_module_config: Arc<ModuleConfig>,
     pub tm_factory: Arc<Fn() -> Result<TargetMachineRef, String> + Send + Sync>,
+    pub msvc_imps_needed: bool,
+    pub target_pointer_width: String,
 
     // Number of cgus excluding the allocator/metadata modules
     pub total_cgus: usize,
@@ -586,6 +591,10 @@ unsafe fn codegen(cgcx: &CodegenContext,
     let module_name = Some(&module_name[..]);
     let handlers = DiagnosticHandlers::new(cgcx, diag_handler, llcx);
 
+    if cgcx.msvc_imps_needed {
+        create_msvc_imps(cgcx, llcx, llmod);
+    }
+
     // A codegen-specific pass manager is used to generate object
     // files for an LLVM module.
     //
@@ -1300,6 +1309,8 @@ fn start_executing_work(tcx: TyCtxt,
         allocator_module_config: allocator_config,
         tm_factory: target_machine_factory(tcx.sess),
         total_cgus,
+        msvc_imps_needed: msvc_imps_needed(tcx),
+        target_pointer_width: tcx.sess.target.target.target_pointer_width.clone(),
     };
 
     // This is the "main loop" of parallel work happening for parallel codegen.
@@ -2133,3 +2144,51 @@ pub fn submit_translated_module_to_llvm(tcx: TyCtxt,
         cost,
     })));
 }
+
+fn msvc_imps_needed(tcx: TyCtxt) -> bool {
+    tcx.sess.target.target.options.is_like_msvc &&
+        tcx.sess.crate_types.borrow().iter().any(|ct| *ct == config::CrateTypeRlib)
+}
+
+// Create a `__imp_<symbol> = &symbol` global for every public static `symbol`.
+// This is required to satisfy `dllimport` references to static data in .rlibs
+// when using MSVC linker.  We do this only for data, as linker can fix up
+// code references on its own.
+// See #26591, #27438
+fn create_msvc_imps(cgcx: &CodegenContext, llcx: ContextRef, llmod: ModuleRef) {
+    if !cgcx.msvc_imps_needed {
+        return
+    }
+    // The x86 ABI seems to require that leading underscores are added to symbol
+    // names, so we need an extra underscore on 32-bit. There's also a leading
+    // '\x01' here which disables LLVM's symbol mangling (e.g. no extra
+    // underscores added in front).
+    let prefix = if cgcx.target_pointer_width == "32" {
+        "\x01__imp__"
+    } else {
+        "\x01__imp_"
+    };
+    unsafe {
+        let i8p_ty = Type::i8p_llcx(llcx);
+        let globals = base::iter_globals(llmod)
+            .filter(|&val| {
+                llvm::LLVMRustGetLinkage(val) == llvm::Linkage::ExternalLinkage &&
+                    llvm::LLVMIsDeclaration(val) == 0
+            })
+            .map(move |val| {
+                let name = CStr::from_ptr(llvm::LLVMGetValueName(val));
+                let mut imp_name = prefix.as_bytes().to_vec();
+                imp_name.extend(name.to_bytes());
+                let imp_name = CString::new(imp_name).unwrap();
+                (imp_name, val)
+            })
+            .collect::<Vec<_>>();
+        for (imp_name, val) in globals {
+            let imp = llvm::LLVMAddGlobal(llmod,
+                                          i8p_ty.to_ref(),
+                                          imp_name.as_ptr() as *const _);
+            llvm::LLVMSetInitializer(imp, consts::ptrcast(val, i8p_ty));
+            llvm::LLVMRustSetLinkage(imp, llvm::Linkage::ExternalLinkage);
+        }
+    }
+}

src/librustc_trans/base.rs

@@ -78,7 +78,7 @@ use rustc::util::nodemap::{NodeSet, FxHashMap, FxHashSet, DefIdSet};
 use CrateInfo;
 
 use std::any::Any;
-use std::ffi::{CStr, CString};
+use std::ffi::CString;
 use std::str;
 use std::sync::Arc;
 use std::time::{Instant, Duration};
@@ -812,47 +812,7 @@ fn write_metadata<'a, 'gcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
     return (metadata_llcx, metadata_llmod, metadata, hashes);
 }
 
-// Create a `__imp_<symbol> = &symbol` global for every public static `symbol`.
-// This is required to satisfy `dllimport` references to static data in .rlibs
-// when using MSVC linker.  We do this only for data, as linker can fix up
-// code references on its own.
-// See #26591, #27438
-fn create_imps(sess: &Session,
-               llvm_module: &ModuleLlvm) {
-    // The x86 ABI seems to require that leading underscores are added to symbol
-    // names, so we need an extra underscore on 32-bit. There's also a leading
-    // '\x01' here which disables LLVM's symbol mangling (e.g. no extra
-    // underscores added in front).
-    let prefix = if sess.target.target.target_pointer_width == "32" {
-        "\x01__imp__"
-    } else {
-        "\x01__imp_"
-    };
-    unsafe {
-        let exported: Vec<_> = iter_globals(llvm_module.llmod)
-                                   .filter(|&val| {
-                                       llvm::LLVMRustGetLinkage(val) ==
-                                       llvm::Linkage::ExternalLinkage &&
-                                       llvm::LLVMIsDeclaration(val) == 0
-                                   })
-                                   .collect();
-
-        let i8p_ty = Type::i8p_llcx(llvm_module.llcx);
-        for val in exported {
-            let name = CStr::from_ptr(llvm::LLVMGetValueName(val));
-            let mut imp_name = prefix.as_bytes().to_vec();
-            imp_name.extend(name.to_bytes());
-            let imp_name = CString::new(imp_name).unwrap();
-            let imp = llvm::LLVMAddGlobal(llvm_module.llmod,
-                                          i8p_ty.to_ref(),
-                                          imp_name.as_ptr() as *const _);
-            llvm::LLVMSetInitializer(imp, consts::ptrcast(val, i8p_ty));
-            llvm::LLVMRustSetLinkage(imp, llvm::Linkage::ExternalLinkage);
-        }
-    }
-}
-
-struct ValueIter {
+pub struct ValueIter {
     cur: ValueRef,
     step: unsafe extern "C" fn(ValueRef) -> ValueRef,
 }
@@ -871,7 +831,7 @@ impl Iterator for ValueIter {
     }
 }
 
-fn iter_globals(llmod: llvm::ModuleRef) -> ValueIter {
+pub fn iter_globals(llmod: llvm::ModuleRef) -> ValueIter {
     unsafe {
         ValueIter {
             cur: llvm::LLVMGetFirstGlobal(llmod),
@@ -1437,12 +1397,6 @@ fn compile_codegen_unit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 tm: create_target_machine(ccx.sess()),
             };
 
-            // Adjust exported symbols for MSVC dllimport
-            if ccx.sess().target.target.options.is_like_msvc &&
-               ccx.sess().crate_types.borrow().iter().any(|ct| *ct == config::CrateTypeRlib) {
-                create_imps(ccx.sess(), &llvm_module);
-            }
-
             ModuleTranslation {
                 name: cgu_name,
                 source: ModuleSource::Translated(llvm_module),

src/test/run-pass/thinlto/auxiliary/msvc-imp-present.rs

@@ -0,0 +1,21 @@
+// 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.
+
+// no-prefer-dynamic
+// compile-flags: -Z thinlto -C codegen-units=8 -C prefer-dynamic
+
+#![crate_type = "rlib"]
+#![crate_type = "dylib"]
+
+pub static A: u32 = 43;
+
+pub mod a {
+    pub static A: u32 = 43;
+}

src/test/run-pass/thinlto/msvc-imp-present.rs

@@ -0,0 +1,31 @@
+// 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.
+
+// aux-build:msvc-imp-present.rs
+// compile-flags: -Z thinlto -C codegen-units=8
+// min-llvm-version: 4.0
+// no-prefer-dynamic
+
+// On MSVC we have a "hack" where we emit symbols that look like `_imp_$name`
+// for all exported statics. This is done because we apply `dllimport` to all
+// imported constants and this allows everything to actually link correctly.
+//
+// The ThinLTO passes aggressively remove symbols if they can, and this test
+// asserts that the ThinLTO passes don't remove these compiler-generated
+// `_imp_*` symbols. The external library that we link in here is compiled with
+// ThinLTO and multiple codegen units and has a few exported constants. Note
+// that we also namely compile the library as both a dylib and an rlib, but we
+// link the rlib to ensure that we assert those generated symbols exist.
+
+extern crate msvc_imp_present as bar;
+
+fn main() {
+    println!("{}", bar::A);
+}