src/librustc_trans/back/linker.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::collections::HashMap;
  12 use std::ffi::OsString;
  13 use std::fs::{self, File};
  14 use std::io::prelude::*;
  15 use std::io::{self, BufWriter};
  16 use std::path::{Path, PathBuf};
  17 use std::process::Command;
  18
  19 use context::SharedCrateContext;
  20 use monomorphize::Instance;
  21
  22 use back::archive;
  23 use middle::dependency_format::Linkage;
  24 use rustc::hir::def_id::CrateNum;
  25 use session::Session;
  26 use session::config::CrateType;
  27 use session::config;
  28
  29 /// For all the linkers we support, and information they might
  30 /// need out of the shared crate context before we get rid of it.
  31 pub struct LinkerInfo {
  32     exports: HashMap<CrateType, Vec<String>>,
  33 }
  34
  35 impl<'a, 'tcx> LinkerInfo {
  36     pub fn new(scx: &SharedCrateContext<'a, 'tcx>,
  37                reachable: &[String]) -> LinkerInfo {
  38         LinkerInfo {
  39             exports: scx.sess().crate_types.borrow().iter().map(|&c| {
  40                 (c, exported_symbols(scx, reachable, c))
  41             }).collect(),
  42         }
  43     }
  44
  45     pub fn to_linker(&'a self,
  46                      cmd: &'a mut Command,
  47                      sess: &'a Session) -> Box<Linker+'a> {
  48         if sess.target.target.options.is_like_msvc {
  49             Box::new(MsvcLinker {
  50                 cmd: cmd,
  51                 sess: sess,
  52                 info: self
  53             }) as Box<Linker>
  54         } else {
  55             Box::new(GnuLinker {
  56                 cmd: cmd,
  57                 sess: sess,
  58                 info: self
  59             }) as Box<Linker>
  60         }
  61     }
  62 }
  63
  64 /// Linker abstraction used by back::link to build up the command to invoke a
  65 /// linker.
  66 ///
  67 /// This trait is the total list of requirements needed by `back::link` and
  68 /// represents the meaning of each option being passed down. This trait is then
  69 /// used to dispatch on whether a GNU-like linker (generally `ld.exe`) or an
  70 /// MSVC linker (e.g. `link.exe`) is being used.
  71 pub trait Linker {
  72     fn link_dylib(&mut self, lib: &str);
  73     fn link_rust_dylib(&mut self, lib: &str, path: &Path);
  74     fn link_framework(&mut self, framework: &str);
  75     fn link_staticlib(&mut self, lib: &str);
  76     fn link_rlib(&mut self, lib: &Path);
  77     fn link_whole_rlib(&mut self, lib: &Path);
  78     fn link_whole_staticlib(&mut self, lib: &str, search_path: &[PathBuf]);
  79     fn include_path(&mut self, path: &Path);
  80     fn framework_path(&mut self, path: &Path);
  81     fn output_filename(&mut self, path: &Path);
  82     fn add_object(&mut self, path: &Path);
  83     fn gc_sections(&mut self, keep_metadata: bool);
  84     fn position_independent_executable(&mut self);
  85     fn optimize(&mut self);
  86     fn debuginfo(&mut self);
  87     fn no_default_libraries(&mut self);
  88     fn build_dylib(&mut self, out_filename: &Path);
  89     fn args(&mut self, args: &[String]);
  90     fn hint_static(&mut self);
  91     fn hint_dynamic(&mut self);
  92     fn whole_archives(&mut self);
  93     fn no_whole_archives(&mut self);
  94     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType);
  95     fn subsystem(&mut self, subsystem: &str);
  96 }
  97
  98 pub struct GnuLinker<'a> {
  99     cmd: &'a mut Command,
 100     sess: &'a Session,
 101     info: &'a LinkerInfo
 102 }
 103
 104 impl<'a> GnuLinker<'a> {
 105     fn takes_hints(&self) -> bool {
 106         !self.sess.target.target.options.is_like_osx
 107     }
 108 }
 109
 110 impl<'a> Linker for GnuLinker<'a> {
 111     fn link_dylib(&mut self, lib: &str) { self.cmd.arg("-l").arg(lib); }
 112     fn link_staticlib(&mut self, lib: &str) { self.cmd.arg("-l").arg(lib); }
 113     fn link_rlib(&mut self, lib: &Path) { self.cmd.arg(lib); }
 114     fn include_path(&mut self, path: &Path) { self.cmd.arg("-L").arg(path); }
 115     fn framework_path(&mut self, path: &Path) { self.cmd.arg("-F").arg(path); }
 116     fn output_filename(&mut self, path: &Path) { self.cmd.arg("-o").arg(path); }
 117     fn add_object(&mut self, path: &Path) { self.cmd.arg(path); }
 118     fn position_independent_executable(&mut self) { self.cmd.arg("-pie"); }
 119     fn args(&mut self, args: &[String]) { self.cmd.args(args); }
 120
 121     fn link_rust_dylib(&mut self, lib: &str, _path: &Path) {
 122         self.cmd.arg("-l").arg(lib);
 123     }
 124
 125     fn link_framework(&mut self, framework: &str) {
 126         self.cmd.arg("-framework").arg(framework);
 127     }
 128
 129     fn link_whole_staticlib(&mut self, lib: &str, search_path: &[PathBuf]) {
 130         let target = &self.sess.target.target;
 131         if !target.options.is_like_osx {
 132             self.cmd.arg("-Wl,--whole-archive")
 133                     .arg("-l").arg(lib)
 134                     .arg("-Wl,--no-whole-archive");
 135         } else {
 136             // -force_load is the OSX equivalent of --whole-archive, but it
 137             // involves passing the full path to the library to link.
 138             let mut v = OsString::from("-Wl,-force_load,");
 139             v.push(&archive::find_library(lib, search_path, &self.sess));
 140             self.cmd.arg(&v);
 141         }
 142     }
 143
 144     fn link_whole_rlib(&mut self, lib: &Path) {
 145         if self.sess.target.target.options.is_like_osx {
 146             let mut v = OsString::from("-Wl,-force_load,");
 147             v.push(lib);
 148             self.cmd.arg(&v);
 149         } else {
 150             self.cmd.arg("-Wl,--whole-archive").arg(lib)
 151                     .arg("-Wl,--no-whole-archive");
 152         }
 153     }
 154
 155     fn gc_sections(&mut self, keep_metadata: bool) {
 156         // The dead_strip option to the linker specifies that functions and data
 157         // unreachable by the entry point will be removed. This is quite useful
 158         // with Rust's compilation model of compiling libraries at a time into
 159         // one object file. For example, this brings hello world from 1.7MB to
 160         // 458K.
 161         //
 162         // Note that this is done for both executables and dynamic libraries. We
 163         // won't get much benefit from dylibs because LLVM will have already
 164         // stripped away as much as it could. This has not been seen to impact
 165         // link times negatively.
 166         //
 167         // -dead_strip can't be part of the pre_link_args because it's also used
 168         // for partial linking when using multiple codegen units (-r).  So we
 169         // insert it here.
 170         if self.sess.target.target.options.is_like_osx {
 171             self.cmd.arg("-Wl,-dead_strip");
 172         } else if self.sess.target.target.options.is_like_solaris {
 173             self.cmd.arg("-Wl,-z");
 174             self.cmd.arg("-Wl,ignore");
 175
 176         // If we're building a dylib, we don't use --gc-sections because LLVM
 177         // has already done the best it can do, and we also don't want to
 178         // eliminate the metadata. If we're building an executable, however,
 179         // --gc-sections drops the size of hello world from 1.8MB to 597K, a 67%
 180         // reduction.
 181         } else if !keep_metadata {
 182             self.cmd.arg("-Wl,--gc-sections");
 183         }
 184     }
 185
 186     fn optimize(&mut self) {
 187         if !self.sess.target.target.options.linker_is_gnu { return }
 188
 189         // GNU-style linkers support optimization with -O. GNU ld doesn't
 190         // need a numeric argument, but other linkers do.
 191         if self.sess.opts.optimize == config::OptLevel::Default ||
 192            self.sess.opts.optimize == config::OptLevel::Aggressive {
 193             self.cmd.arg("-Wl,-O1");
 194         }
 195     }
 196
 197     fn debuginfo(&mut self) {
 198         // Don't do anything special here for GNU-style linkers.
 199     }
 200
 201     fn no_default_libraries(&mut self) {
 202         self.cmd.arg("-nodefaultlibs");
 203     }
 204
 205     fn build_dylib(&mut self, out_filename: &Path) {
 206         // On mac we need to tell the linker to let this library be rpathed
 207         if self.sess.target.target.options.is_like_osx {
 208             self.cmd.args(&["-dynamiclib", "-Wl,-dylib"]);
 209
 210             if self.sess.opts.cg.rpath {
 211                 let mut v = OsString::from("-Wl,-install_name,@rpath/");
 212                 v.push(out_filename.file_name().unwrap());
 213                 self.cmd.arg(&v);
 214             }
 215         } else {
 216             self.cmd.arg("-shared");
 217         }
 218     }
 219
 220     fn whole_archives(&mut self) {
 221         if !self.takes_hints() { return }
 222         self.cmd.arg("-Wl,--whole-archive");
 223     }
 224
 225     fn no_whole_archives(&mut self) {
 226         if !self.takes_hints() { return }
 227         self.cmd.arg("-Wl,--no-whole-archive");
 228     }
 229
 230     fn hint_static(&mut self) {
 231         if !self.takes_hints() { return }
 232         self.cmd.arg("-Wl,-Bstatic");
 233     }
 234
 235     fn hint_dynamic(&mut self) {
 236         if !self.takes_hints() { return }
 237         self.cmd.arg("-Wl,-Bdynamic");
 238     }
 239
 240     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType) {
 241         // If we're compiling a dylib, then we let symbol visibility in object
 242         // files to take care of whether they're exported or not.
 243         //
 244         // If we're compiling a cdylib, however, we manually create a list of
 245         // exported symbols to ensure we don't expose any more. The object files
 246         // have far more public symbols than we actually want to export, so we
 247         // hide them all here.
 248         if crate_type == CrateType::CrateTypeDylib ||
 249            crate_type == CrateType::CrateTypeProcMacro {
 250             return
 251         }
 252
 253         let mut arg = OsString::new();
 254         let path = tmpdir.join("list");
 255
 256         if self.sess.target.target.options.is_like_solaris {
 257             let res = (|| -> io::Result<()> {
 258                 let mut f = BufWriter::new(File::create(&path)?);
 259                 writeln!(f, "{{\n  global:")?;
 260                 for sym in self.info.exports[&crate_type].iter() {
 261                     writeln!(f, "    {};", sym)?;
 262                 }
 263                 writeln!(f, "\n  local:\n    *;\n}};")?;
 264                 Ok(())
 265             })();
 266             if let Err(e) = res {
 267                 self.sess.fatal(&format!("failed to write version script: {}", e));
 268             }
 269
 270             arg.push("-Wl,-M,");
 271             arg.push(&path);
 272         } else {
 273             let prefix = if self.sess.target.target.options.is_like_osx {
 274                 "_"
 275             } else {
 276                 ""
 277             };
 278             let res = (|| -> io::Result<()> {
 279                 let mut f = BufWriter::new(File::create(&path)?);
 280                 for sym in self.info.exports[&crate_type].iter() {
 281                     writeln!(f, "{}{}", prefix, sym)?;
 282                 }
 283                 Ok(())
 284             })();
 285             if let Err(e) = res {
 286                 self.sess.fatal(&format!("failed to write lib.def file: {}", e));
 287             }
 288             if self.sess.target.target.options.is_like_osx {
 289                 arg.push("-Wl,-exported_symbols_list,");
 290             } else {
 291                 arg.push("-Wl,--retain-symbols-file=");
 292             }
 293             arg.push(&path);
 294         }
 295
 296         self.cmd.arg(arg);
 297     }
 298
 299     fn subsystem(&mut self, subsystem: &str) {
 300         self.cmd.arg(&format!("-Wl,--subsystem,{}", subsystem));
 301     }
 302 }
 303
 304 pub struct MsvcLinker<'a> {
 305     cmd: &'a mut Command,
 306     sess: &'a Session,
 307     info: &'a LinkerInfo
 308 }
 309
 310 impl<'a> Linker for MsvcLinker<'a> {
 311     fn link_rlib(&mut self, lib: &Path) { self.cmd.arg(lib); }
 312     fn add_object(&mut self, path: &Path) { self.cmd.arg(path); }
 313     fn args(&mut self, args: &[String]) { self.cmd.args(args); }
 314
 315     fn build_dylib(&mut self, out_filename: &Path) {
 316         self.cmd.arg("/DLL");
 317         let mut arg: OsString = "/IMPLIB:".into();
 318         arg.push(out_filename.with_extension("dll.lib"));
 319         self.cmd.arg(arg);
 320     }
 321
 322     fn gc_sections(&mut self, _keep_metadata: bool) {
 323         self.cmd.arg("/OPT:REF,ICF");
 324     }
 325
 326     fn link_dylib(&mut self, lib: &str) {
 327         self.cmd.arg(&format!("{}.lib", lib));
 328     }
 329
 330     fn link_rust_dylib(&mut self, lib: &str, path: &Path) {
 331         // When producing a dll, the MSVC linker may not actually emit a
 332         // `foo.lib` file if the dll doesn't actually export any symbols, so we
 333         // check to see if the file is there and just omit linking to it if it's
 334         // not present.
 335         let name = format!("{}.dll.lib", lib);
 336         if fs::metadata(&path.join(&name)).is_ok() {
 337             self.cmd.arg(name);
 338         }
 339     }
 340
 341     fn link_staticlib(&mut self, lib: &str) {
 342         self.cmd.arg(&format!("{}.lib", lib));
 343     }
 344
 345     fn position_independent_executable(&mut self) {
 346         // noop
 347     }
 348
 349     fn no_default_libraries(&mut self) {
 350         // Currently we don't pass the /NODEFAULTLIB flag to the linker on MSVC
 351         // as there's been trouble in the past of linking the C++ standard
 352         // library required by LLVM. This likely needs to happen one day, but
 353         // in general Windows is also a more controlled environment than
 354         // Unix, so it's not necessarily as critical that this be implemented.
 355         //
 356         // Note that there are also some licensing worries about statically
 357         // linking some libraries which require a specific agreement, so it may
 358         // not ever be possible for us to pass this flag.
 359     }
 360
 361     fn include_path(&mut self, path: &Path) {
 362         let mut arg = OsString::from("/LIBPATH:");
 363         arg.push(path);
 364         self.cmd.arg(&arg);
 365     }
 366
 367     fn output_filename(&mut self, path: &Path) {
 368         let mut arg = OsString::from("/OUT:");
 369         arg.push(path);
 370         self.cmd.arg(&arg);
 371     }
 372
 373     fn framework_path(&mut self, _path: &Path) {
 374         bug!("frameworks are not supported on windows")
 375     }
 376     fn link_framework(&mut self, _framework: &str) {
 377         bug!("frameworks are not supported on windows")
 378     }
 379
 380     fn link_whole_staticlib(&mut self, lib: &str, _search_path: &[PathBuf]) {
 381         // not supported?
 382         self.link_staticlib(lib);
 383     }
 384     fn link_whole_rlib(&mut self, path: &Path) {
 385         // not supported?
 386         self.link_rlib(path);
 387     }
 388     fn optimize(&mut self) {
 389         // Needs more investigation of `/OPT` arguments
 390     }
 391
 392     fn debuginfo(&mut self) {
 393         // This will cause the Microsoft linker to generate a PDB file
 394         // from the CodeView line tables in the object files.
 395         self.cmd.arg("/DEBUG");
 396     }
 397
 398     fn whole_archives(&mut self) {
 399         // hints not supported?
 400     }
 401     fn no_whole_archives(&mut self) {
 402         // hints not supported?
 403     }
 404
 405     // On windows static libraries are of the form `foo.lib` and dynamic
 406     // libraries are not linked against directly, but rather through their
 407     // import libraries also called `foo.lib`. As a result there's no
 408     // possibility for a native library to appear both dynamically and
 409     // statically in the same folder so we don't have to worry about hints like
 410     // we do on Unix platforms.
 411     fn hint_static(&mut self) {}
 412     fn hint_dynamic(&mut self) {}
 413
 414     // Currently the compiler doesn't use `dllexport` (an LLVM attribute) to
 415     // export symbols from a dynamic library. When building a dynamic library,
 416     // however, we're going to want some symbols exported, so this function
 417     // generates a DEF file which lists all the symbols.
 418     //
 419     // The linker will read this `*.def` file and export all the symbols from
 420     // the dynamic library. Note that this is not as simple as just exporting
 421     // all the symbols in the current crate (as specified by `trans.reachable`)
 422     // but rather we also need to possibly export the symbols of upstream
 423     // crates. Upstream rlibs may be linked statically to this dynamic library,
 424     // in which case they may continue to transitively be used and hence need
 425     // their symbols exported.
 426     fn export_symbols(&mut self,
 427                       tmpdir: &Path,
 428                       crate_type: CrateType) {
 429         let path = tmpdir.join("lib.def");
 430         let res = (|| -> io::Result<()> {
 431             let mut f = BufWriter::new(File::create(&path)?);
 432
 433             // Start off with the standard module name header and then go
 434             // straight to exports.
 435             writeln!(f, "LIBRARY")?;
 436             writeln!(f, "EXPORTS")?;
 437             for symbol in self.info.exports[&crate_type].iter() {
 438                 writeln!(f, "  {}", symbol)?;
 439             }
 440             Ok(())
 441         })();
 442         if let Err(e) = res {
 443             self.sess.fatal(&format!("failed to write lib.def file: {}", e));
 444         }
 445         let mut arg = OsString::from("/DEF:");
 446         arg.push(path);
 447         self.cmd.arg(&arg);
 448     }
 449
 450     fn subsystem(&mut self, subsystem: &str) {
 451         // Note that previous passes of the compiler validated this subsystem,
 452         // so we just blindly pass it to the linker.
 453         self.cmd.arg(&format!("/SUBSYSTEM:{}", subsystem));
 454
 455         // Windows has two subsystems we're interested in right now, the console
 456         // and windows subsystems. These both implicitly have different entry
 457         // points (starting symbols). The console entry point starts with
 458         // `mainCRTStartup` and the windows entry point starts with
 459         // `WinMainCRTStartup`. These entry points, defined in system libraries,
 460         // will then later probe for either `main` or `WinMain`, respectively to
 461         // start the application.
 462         //
 463         // In Rust we just always generate a `main` function so we want control
 464         // to always start there, so we force the entry point on the windows
 465         // subsystem to be `mainCRTStartup` to get everything booted up
 466         // correctly.
 467         //
 468         // For more information see RFC #1665
 469         if subsystem == "windows" {
 470             self.cmd.arg("/ENTRY:mainCRTStartup");
 471         }
 472     }
 473 }
 474
 475 fn exported_symbols(scx: &SharedCrateContext,
 476                     reachable: &[String],
 477                     crate_type: CrateType)
 478                     -> Vec<String> {
 479     // See explanation in GnuLinker::export_symbols, for
 480     // why we don't ever need dylib symbols on non-MSVC.
 481     if crate_type == CrateType::CrateTypeDylib ||
 482        crate_type == CrateType::CrateTypeProcMacro {
 483         if !scx.sess().target.target.options.is_like_msvc {
 484             return vec![];
 485         }
 486     }
 487
 488     let mut symbols = reachable.to_vec();
 489
 490     // If we're producing anything other than a dylib then the `reachable` array
 491     // above is the exhaustive set of symbols we should be exporting.
 492     //
 493     // For dylibs, however, we need to take a look at how all upstream crates
 494     // are linked into this dynamic library. For all statically linked
 495     // libraries we take all their reachable symbols and emit them as well.
 496     if crate_type != CrateType::CrateTypeDylib {
 497         return symbols
 498     }
 499
 500     let cstore = &scx.sess().cstore;
 501     let formats = scx.sess().dependency_formats.borrow();
 502     let deps = formats[&crate_type].iter();
 503     symbols.extend(deps.enumerate().filter_map(|(i, f)| {
 504         if *f == Linkage::Static {
 505             Some(CrateNum::new(i + 1))
 506         } else {
 507             None
 508         }
 509     }).flat_map(|cnum| {
 510         cstore.reachable_ids(cnum)
 511     }).map(|did| -> String {
 512         Instance::mono(scx, did).symbol_name(scx)
 513     }));
 514     symbols
 515 }