1 // Copyright 2014 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.
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.
11 //! Resolution of mixing rlibs and dylibs
13 //! When producing a final artifact, such as a dynamic library, the compiler has
14 //! a choice between linking an rlib or linking a dylib of all upstream
15 //! dependencies. The linking phase must guarantee, however, that a library only
16 //! show up once in the object file. For example, it is illegal for library A to
17 //! be statically linked to B and C in separate dylibs, and then link B and C
18 //! into a crate D (because library A appears twice).
20 //! The job of this module is to calculate what format each upstream crate
21 //! should be used when linking each output type requested in this session. This
22 //! generally follows this set of rules:
24 //! 1. Each library must appear exactly once in the output.
25 //! 2. Each rlib contains only one library (it's just an object file)
26 //! 3. Each dylib can contain more than one library (due to static linking),
27 //! and can also bring in many dynamic dependencies.
29 //! With these constraints in mind, it's generally a very difficult problem to
30 //! find a solution that's not "all rlibs" or "all dylibs". I have suspicions
31 //! that NP-ness may come into the picture here...
33 //! The current selection algorithm below looks mostly similar to:
35 //! 1. If static linking is required, then require all upstream dependencies
36 //! to be available as rlibs. If not, generate an error.
37 //! 2. If static linking is requested (generating an executable), then
38 //! attempt to use all upstream dependencies as rlibs. If any are not
39 //! found, bail out and continue to step 3.
40 //! 3. Static linking has failed, at least one library must be dynamically
41 //! linked. Apply a heuristic by greedily maximizing the number of
42 //! dynamically linked libraries.
43 //! 4. Each upstream dependency available as a dynamic library is
44 //! registered. The dependencies all propagate, adding to a map. It is
45 //! possible for a dylib to add a static library as a dependency, but it
46 //! is illegal for two dylibs to add the same static library as a
47 //! dependency. The same dylib can be added twice. Additionally, it is
48 //! illegal to add a static dependency when it was previously found as a
49 //! dylib (and vice versa)
50 //! 5. After all dynamic dependencies have been traversed, re-traverse the
51 //! remaining dependencies and add them statically (if they haven't been
54 //! While not perfect, this algorithm should help support use-cases such as leaf
55 //! dependencies being static while the larger tree of inner dependencies are
56 //! all dynamic. This isn't currently very well battle tested, so it will likely
57 //! fall short in some use cases.
59 //! Currently, there is no way to specify the preference of linkage with a
60 //! particular library (other than a global dynamic/static switch).
61 //! Additionally, the algorithm is geared towards finding *any* solution rather
62 //! than finding a number of solutions (there are normally quite a few).
64 use hir::def_id::CrateNum;
69 use middle::cstore::{self, DepKind};
70 use middle::cstore::LinkagePreference::{self, RequireStatic, RequireDynamic};
71 use util::nodemap::FxHashMap;
72 use rustc_target::spec::PanicStrategy;
74 /// A list of dependencies for a certain crate type.
76 /// The length of this vector is the same as the number of external crates used.
77 /// The value is None if the crate does not need to be linked (it was found
78 /// statically in another dylib), or Some(kind) if it needs to be linked as
79 /// `kind` (either static or dynamic).
80 pub type DependencyList = Vec<Linkage>;
82 /// A mapping of all required dependencies for a particular flavor of output.
84 /// This is local to the tcx, and is generally relevant to one session.
85 pub type Dependencies = FxHashMap<config::CrateType, DependencyList>;
87 #[derive(Copy, Clone, PartialEq, Debug)]
95 pub fn calculate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
97 let mut fmts = FxHashMap();
98 for &ty in sess.crate_types.borrow().iter() {
99 let linkage = calculate_type(tcx, ty);
100 verify_ok(tcx, &linkage);
101 fmts.insert(ty, linkage);
103 sess.abort_if_errors();
104 sess.dependency_formats.set(fmts);
107 fn calculate_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
108 ty: config::CrateType) -> DependencyList {
110 let sess = &tcx.sess;
112 if !sess.opts.output_types.should_codegen() {
116 let preferred_linkage = match ty {
117 // cdylibs must have all static dependencies.
118 config::CrateType::Cdylib => Linkage::Static,
120 // Generating a dylib without `-C prefer-dynamic` means that we're going
121 // to try to eagerly statically link all dependencies. This is normally
122 // done for end-product dylibs, not intermediate products.
123 config::CrateType::Dylib if !sess.opts.cg.prefer_dynamic => Linkage::Static,
124 config::CrateType::Dylib => Linkage::Dynamic,
126 // If the global prefer_dynamic switch is turned off, or the final
127 // executable will be statically linked, prefer static crate linkage.
128 config::CrateType::Executable if !sess.opts.cg.prefer_dynamic ||
129 sess.crt_static() => Linkage::Static,
130 config::CrateType::Executable => Linkage::Dynamic,
132 // proc-macro crates are required to be dylibs, and they're currently
133 // required to link to libsyntax as well.
134 config::CrateType::ProcMacro => Linkage::Dynamic,
136 // No linkage happens with rlibs, we just needed the metadata (which we
137 // got long ago), so don't bother with anything.
138 config::CrateType::Rlib => Linkage::NotLinked,
140 // staticlibs must have all static dependencies.
141 config::CrateType::Staticlib => Linkage::Static,
144 if preferred_linkage == Linkage::NotLinked {
145 // If the crate is not linked, there are no link-time dependencies.
149 if preferred_linkage == Linkage::Static {
150 // Attempt static linkage first. For dylibs and executables, we may be
151 // able to retry below with dynamic linkage.
152 if let Some(v) = attempt_static(tcx) {
156 // Staticlibs, cdylibs, and static executables must have all static
157 // dependencies. If any are not found, generate some nice pretty errors.
158 if ty == config::CrateType::Cdylib || ty == config::CrateType::Staticlib ||
159 (ty == config::CrateType::Executable && sess.crt_static() &&
160 !sess.target.target.options.crt_static_allows_dylibs) {
161 for &cnum in tcx.crates().iter() {
162 if tcx.dep_kind(cnum).macros_only() { continue }
163 let src = tcx.used_crate_source(cnum);
164 if src.rlib.is_some() { continue }
165 sess.err(&format!("crate `{}` required to be available in rlib format, \
166 but was not found in this form",
167 tcx.crate_name(cnum)));
173 let mut formats = FxHashMap();
175 // Sweep all crates for found dylibs. Add all dylibs, as well as their
176 // dependencies, ensuring there are no conflicts. The only valid case for a
177 // dependency to be relied upon twice is for both cases to rely on a dylib.
178 for &cnum in tcx.crates().iter() {
179 if tcx.dep_kind(cnum).macros_only() { continue }
180 let name = tcx.crate_name(cnum);
181 let src = tcx.used_crate_source(cnum);
182 if src.dylib.is_some() {
183 info!("adding dylib: {}", name);
184 add_library(tcx, cnum, RequireDynamic, &mut formats);
185 let deps = tcx.dylib_dependency_formats(cnum);
186 for &(depnum, style) in deps.iter() {
187 info!("adding {:?}: {}", style, tcx.crate_name(depnum));
188 add_library(tcx, depnum, style, &mut formats);
193 // Collect what we've got so far in the return vector.
194 let last_crate = tcx.crates().len();
195 let mut ret = (1..last_crate+1).map(|cnum| {
196 match formats.get(&CrateNum::new(cnum)) {
197 Some(&RequireDynamic) => Linkage::Dynamic,
198 Some(&RequireStatic) => Linkage::IncludedFromDylib,
199 None => Linkage::NotLinked,
201 }).collect::<Vec<_>>();
203 // Run through the dependency list again, and add any missing libraries as
206 // If the crate hasn't been included yet and it's not actually required
207 // (e.g. it's an allocator) then we skip it here as well.
208 for &cnum in tcx.crates().iter() {
209 let src = tcx.used_crate_source(cnum);
210 if src.dylib.is_none() &&
211 !formats.contains_key(&cnum) &&
212 tcx.dep_kind(cnum) == DepKind::Explicit {
213 assert!(src.rlib.is_some() || src.rmeta.is_some());
214 info!("adding staticlib: {}", tcx.crate_name(cnum));
215 add_library(tcx, cnum, RequireStatic, &mut formats);
216 ret[cnum.as_usize() - 1] = Linkage::Static;
220 // We've gotten this far because we're emitting some form of a final
221 // artifact which means that we may need to inject dependencies of some
224 // Things like allocators and panic runtimes may not have been activated
225 // quite yet, so do so here.
226 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
227 &|cnum| tcx.is_panic_runtime(cnum));
228 activate_injected_allocator(sess, &mut ret);
230 // When dylib B links to dylib A, then when using B we must also link to A.
231 // It could be the case, however, that the rlib for A is present (hence we
232 // found metadata), but the dylib for A has since been removed.
234 // For situations like this, we perform one last pass over the dependencies,
235 // making sure that everything is available in the requested format.
236 for (cnum, kind) in ret.iter().enumerate() {
237 let cnum = CrateNum::new(cnum + 1);
238 let src = tcx.used_crate_source(cnum);
241 Linkage::IncludedFromDylib => {}
242 Linkage::Static if src.rlib.is_some() => continue,
243 Linkage::Dynamic if src.dylib.is_some() => continue,
245 let kind = match kind {
246 Linkage::Static => "rlib",
249 sess.err(&format!("crate `{}` required to be available in {} format, \
250 but was not found in this form",
251 tcx.crate_name(cnum), kind));
259 fn add_library(tcx: TyCtxt,
261 link: LinkagePreference,
262 m: &mut FxHashMap<CrateNum, LinkagePreference>) {
265 // If the linkages differ, then we'd have two copies of the library
266 // if we continued linking. If the linkages are both static, then we
267 // would also have two copies of the library (static from two
268 // different locations).
270 // This error is probably a little obscure, but I imagine that it
271 // can be refined over time.
272 if link2 != link || link == RequireStatic {
273 tcx.sess.struct_err(&format!("cannot satisfy dependencies so `{}` only \
274 shows up once", tcx.crate_name(cnum)))
275 .help("having upstream crates all available in one format \
276 will likely make this go away")
280 None => { m.insert(cnum, link); }
284 fn attempt_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Option<DependencyList> {
285 let sess = &tcx.sess;
286 let crates = cstore::used_crates(tcx, RequireStatic);
287 if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) {
291 // All crates are available in an rlib format, so we're just going to link
292 // everything in explicitly so long as it's actually required.
293 let last_crate = tcx.crates().len();
294 let mut ret = (1..last_crate+1).map(|cnum| {
295 if tcx.dep_kind(CrateNum::new(cnum)) == DepKind::Explicit {
300 }).collect::<Vec<_>>();
302 // Our allocator/panic runtime may not have been linked above if it wasn't
303 // explicitly linked, which is the case for any injected dependency. Handle
304 // that here and activate them.
305 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
306 &|cnum| tcx.is_panic_runtime(cnum));
307 activate_injected_allocator(sess, &mut ret);
312 // Given a list of how to link upstream dependencies so far, ensure that an
313 // injected dependency is activated. This will not do anything if one was
314 // transitively included already (e.g. via a dylib or explicitly so).
316 // If an injected dependency was not found then we're guaranteed the
317 // metadata::creader module has injected that dependency (not listed as
318 // a required dependency) in one of the session's field. If this field is not
319 // set then this compilation doesn't actually need the dependency and we can
320 // also skip this step entirely.
321 fn activate_injected_dep(injected: Option<CrateNum>,
322 list: &mut DependencyList,
323 replaces_injected: &dyn Fn(CrateNum) -> bool) {
324 for (i, slot) in list.iter().enumerate() {
325 let cnum = CrateNum::new(i + 1);
326 if !replaces_injected(cnum) {
329 if *slot != Linkage::NotLinked {
333 if let Some(injected) = injected {
334 let idx = injected.as_usize() - 1;
335 assert_eq!(list[idx], Linkage::NotLinked);
336 list[idx] = Linkage::Static;
340 fn activate_injected_allocator(sess: &session::Session,
341 list: &mut DependencyList) {
342 let cnum = match sess.injected_allocator.get() {
346 let idx = cnum.as_usize() - 1;
347 if list[idx] == Linkage::NotLinked {
348 list[idx] = Linkage::Static;
352 // After the linkage for a crate has been determined we need to verify that
353 // there's only going to be one allocator in the output.
354 fn verify_ok<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, list: &[Linkage]) {
355 let sess = &tcx.sess;
359 let mut panic_runtime = None;
360 for (i, linkage) in list.iter().enumerate() {
361 if let Linkage::NotLinked = *linkage {
364 let cnum = CrateNum::new(i + 1);
366 if tcx.is_panic_runtime(cnum) {
367 if let Some((prev, _)) = panic_runtime {
368 let prev_name = tcx.crate_name(prev);
369 let cur_name = tcx.crate_name(cnum);
370 sess.err(&format!("cannot link together two \
371 panic runtimes: {} and {}",
372 prev_name, cur_name));
374 panic_runtime = Some((cnum, tcx.panic_strategy(cnum)));
378 // If we found a panic runtime, then we know by this point that it's the
379 // only one, but we perform validation here that all the panic strategy
380 // compilation modes for the whole DAG are valid.
381 if let Some((cnum, found_strategy)) = panic_runtime {
382 let desired_strategy = sess.panic_strategy();
384 // First up, validate that our selected panic runtime is indeed exactly
385 // our same strategy.
386 if found_strategy != desired_strategy {
387 sess.err(&format!("the linked panic runtime `{}` is \
388 not compiled with this crate's \
389 panic strategy `{}`",
390 tcx.crate_name(cnum),
391 desired_strategy.desc()));
394 // Next up, verify that all other crates are compatible with this panic
395 // strategy. If the dep isn't linked, we ignore it, and if our strategy
396 // is abort then it's compatible with everything. Otherwise all crates'
397 // panic strategy must match our own.
398 for (i, linkage) in list.iter().enumerate() {
399 if let Linkage::NotLinked = *linkage {
402 if desired_strategy == PanicStrategy::Abort {
405 let cnum = CrateNum::new(i + 1);
406 let found_strategy = tcx.panic_strategy(cnum);
407 let is_compiler_builtins = tcx.is_compiler_builtins(cnum);
408 if is_compiler_builtins || desired_strategy == found_strategy {
412 sess.err(&format!("the crate `{}` is compiled with the \
413 panic strategy `{}` which is \
414 incompatible with this crate's \
416 tcx.crate_name(cnum),
417 found_strategy.desc(),
418 desired_strategy.desc()));