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;
68 use middle::cstore::{self, DepKind};
69 use middle::cstore::LinkagePreference::{self, RequireStatic, RequireDynamic};
70 use util::nodemap::FxHashMap;
71 use rustc_target::spec::PanicStrategy;
73 /// A list of dependencies for a certain crate type.
75 /// The length of this vector is the same as the number of external crates used.
76 /// The value is None if the crate does not need to be linked (it was found
77 /// statically in another dylib), or Some(kind) if it needs to be linked as
78 /// `kind` (either static or dynamic).
79 pub type DependencyList = Vec<Linkage>;
81 /// A mapping of all required dependencies for a particular flavor of output.
83 /// This is local to the tcx, and is generally relevant to one session.
84 pub type Dependencies = FxHashMap<config::CrateType, DependencyList>;
86 #[derive(Copy, Clone, PartialEq, Debug)]
94 pub fn calculate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
96 let fmts = sess.crate_types.borrow().iter().map(|&ty| {
97 let linkage = calculate_type(tcx, ty);
98 verify_ok(tcx, &linkage);
100 }).collect::<FxHashMap<_, _>>();
101 sess.abort_if_errors();
102 sess.dependency_formats.set(fmts);
105 fn calculate_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
106 ty: config::CrateType) -> DependencyList {
108 let sess = &tcx.sess;
110 if !sess.opts.output_types.should_codegen() {
114 let preferred_linkage = match ty {
115 // cdylibs must have all static dependencies.
116 config::CrateType::Cdylib => Linkage::Static,
118 // Generating a dylib without `-C prefer-dynamic` means that we're going
119 // to try to eagerly statically link all dependencies. This is normally
120 // done for end-product dylibs, not intermediate products.
121 config::CrateType::Dylib if !sess.opts.cg.prefer_dynamic => Linkage::Static,
122 config::CrateType::Dylib => Linkage::Dynamic,
124 // If the global prefer_dynamic switch is turned off, or the final
125 // executable will be statically linked, prefer static crate linkage.
126 config::CrateType::Executable if !sess.opts.cg.prefer_dynamic ||
127 sess.crt_static() => Linkage::Static,
128 config::CrateType::Executable => Linkage::Dynamic,
130 // proc-macro crates are mostly cdylibs, but we also need metadata.
131 config::CrateType::ProcMacro => Linkage::Static,
133 // No linkage happens with rlibs, we just needed the metadata (which we
134 // got long ago), so don't bother with anything.
135 config::CrateType::Rlib => Linkage::NotLinked,
137 // staticlibs must have all static dependencies.
138 config::CrateType::Staticlib => Linkage::Static,
141 if preferred_linkage == Linkage::NotLinked {
142 // If the crate is not linked, there are no link-time dependencies.
146 if preferred_linkage == Linkage::Static {
147 // Attempt static linkage first. For dylibs and executables, we may be
148 // able to retry below with dynamic linkage.
149 if let Some(v) = attempt_static(tcx) {
153 // Staticlibs, cdylibs, and static executables must have all static
154 // dependencies. If any are not found, generate some nice pretty errors.
155 if ty == config::CrateType::Cdylib || ty == config::CrateType::Staticlib ||
156 (ty == config::CrateType::Executable && sess.crt_static() &&
157 !sess.target.target.options.crt_static_allows_dylibs) {
158 for &cnum in tcx.crates().iter() {
159 if tcx.dep_kind(cnum).macros_only() { continue }
160 let src = tcx.used_crate_source(cnum);
161 if src.rlib.is_some() { continue }
162 sess.err(&format!("crate `{}` required to be available in rlib format, \
163 but was not found in this form",
164 tcx.crate_name(cnum)));
170 let mut formats = FxHashMap::default();
172 // Sweep all crates for found dylibs. Add all dylibs, as well as their
173 // dependencies, ensuring there are no conflicts. The only valid case for a
174 // dependency to be relied upon twice is for both cases to rely on a dylib.
175 for &cnum in tcx.crates().iter() {
176 if tcx.dep_kind(cnum).macros_only() { continue }
177 let name = tcx.crate_name(cnum);
178 let src = tcx.used_crate_source(cnum);
179 if src.dylib.is_some() {
180 info!("adding dylib: {}", name);
181 add_library(tcx, cnum, RequireDynamic, &mut formats);
182 let deps = tcx.dylib_dependency_formats(cnum);
183 for &(depnum, style) in deps.iter() {
184 info!("adding {:?}: {}", style, tcx.crate_name(depnum));
185 add_library(tcx, depnum, style, &mut formats);
190 // Collect what we've got so far in the return vector.
191 let last_crate = tcx.crates().len();
192 let mut ret = (1..last_crate+1).map(|cnum| {
193 match formats.get(&CrateNum::new(cnum)) {
194 Some(&RequireDynamic) => Linkage::Dynamic,
195 Some(&RequireStatic) => Linkage::IncludedFromDylib,
196 None => Linkage::NotLinked,
198 }).collect::<Vec<_>>();
200 // Run through the dependency list again, and add any missing libraries as
203 // If the crate hasn't been included yet and it's not actually required
204 // (e.g. it's an allocator) then we skip it here as well.
205 for &cnum in tcx.crates().iter() {
206 let src = tcx.used_crate_source(cnum);
207 if src.dylib.is_none() &&
208 !formats.contains_key(&cnum) &&
209 tcx.dep_kind(cnum) == DepKind::Explicit {
210 assert!(src.rlib.is_some() || src.rmeta.is_some());
211 info!("adding staticlib: {}", tcx.crate_name(cnum));
212 add_library(tcx, cnum, RequireStatic, &mut formats);
213 ret[cnum.as_usize() - 1] = Linkage::Static;
217 // We've gotten this far because we're emitting some form of a final
218 // artifact which means that we may need to inject dependencies of some
221 // Things like allocators and panic runtimes may not have been activated
222 // quite yet, so do so here.
223 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
224 &|cnum| tcx.is_panic_runtime(cnum));
226 // When dylib B links to dylib A, then when using B we must also link to A.
227 // It could be the case, however, that the rlib for A is present (hence we
228 // found metadata), but the dylib for A has since been removed.
230 // For situations like this, we perform one last pass over the dependencies,
231 // making sure that everything is available in the requested format.
232 for (cnum, kind) in ret.iter().enumerate() {
233 let cnum = CrateNum::new(cnum + 1);
234 let src = tcx.used_crate_source(cnum);
237 Linkage::IncludedFromDylib => {}
238 Linkage::Static if src.rlib.is_some() => continue,
239 Linkage::Dynamic if src.dylib.is_some() => continue,
241 let kind = match kind {
242 Linkage::Static => "rlib",
245 sess.err(&format!("crate `{}` required to be available in {} format, \
246 but was not found in this form",
247 tcx.crate_name(cnum), kind));
255 fn add_library(tcx: TyCtxt<'_, '_, '_>,
257 link: LinkagePreference,
258 m: &mut FxHashMap<CrateNum, LinkagePreference>) {
261 // If the linkages differ, then we'd have two copies of the library
262 // if we continued linking. If the linkages are both static, then we
263 // would also have two copies of the library (static from two
264 // different locations).
266 // This error is probably a little obscure, but I imagine that it
267 // can be refined over time.
268 if link2 != link || link == RequireStatic {
269 tcx.sess.struct_err(&format!("cannot satisfy dependencies so `{}` only \
270 shows up once", tcx.crate_name(cnum)))
271 .help("having upstream crates all available in one format \
272 will likely make this go away")
276 None => { m.insert(cnum, link); }
280 fn attempt_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Option<DependencyList> {
281 let sess = &tcx.sess;
282 let crates = cstore::used_crates(tcx, RequireStatic);
283 if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) {
287 // All crates are available in an rlib format, so we're just going to link
288 // everything in explicitly so long as it's actually required.
289 let last_crate = tcx.crates().len();
290 let mut ret = (1..last_crate+1).map(|cnum| {
291 if tcx.dep_kind(CrateNum::new(cnum)) == DepKind::Explicit {
296 }).collect::<Vec<_>>();
298 // Our allocator/panic runtime may not have been linked above if it wasn't
299 // explicitly linked, which is the case for any injected dependency. Handle
300 // that here and activate them.
301 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
302 &|cnum| tcx.is_panic_runtime(cnum));
307 // Given a list of how to link upstream dependencies so far, ensure that an
308 // injected dependency is activated. This will not do anything if one was
309 // transitively included already (e.g. via a dylib or explicitly so).
311 // If an injected dependency was not found then we're guaranteed the
312 // metadata::creader module has injected that dependency (not listed as
313 // a required dependency) in one of the session's field. If this field is not
314 // set then this compilation doesn't actually need the dependency and we can
315 // also skip this step entirely.
316 fn activate_injected_dep(injected: Option<CrateNum>,
317 list: &mut DependencyList,
318 replaces_injected: &dyn Fn(CrateNum) -> bool) {
319 for (i, slot) in list.iter().enumerate() {
320 let cnum = CrateNum::new(i + 1);
321 if !replaces_injected(cnum) {
324 if *slot != Linkage::NotLinked {
328 if let Some(injected) = injected {
329 let idx = injected.as_usize() - 1;
330 assert_eq!(list[idx], Linkage::NotLinked);
331 list[idx] = Linkage::Static;
335 // After the linkage for a crate has been determined we need to verify that
336 // there's only going to be one allocator in the output.
337 fn verify_ok<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, list: &[Linkage]) {
338 let sess = &tcx.sess;
342 let mut panic_runtime = None;
343 for (i, linkage) in list.iter().enumerate() {
344 if let Linkage::NotLinked = *linkage {
347 let cnum = CrateNum::new(i + 1);
349 if tcx.is_panic_runtime(cnum) {
350 if let Some((prev, _)) = panic_runtime {
351 let prev_name = tcx.crate_name(prev);
352 let cur_name = tcx.crate_name(cnum);
353 sess.err(&format!("cannot link together two \
354 panic runtimes: {} and {}",
355 prev_name, cur_name));
357 panic_runtime = Some((cnum, tcx.panic_strategy(cnum)));
361 // If we found a panic runtime, then we know by this point that it's the
362 // only one, but we perform validation here that all the panic strategy
363 // compilation modes for the whole DAG are valid.
364 if let Some((cnum, found_strategy)) = panic_runtime {
365 let desired_strategy = sess.panic_strategy();
367 // First up, validate that our selected panic runtime is indeed exactly
368 // our same strategy.
369 if found_strategy != desired_strategy {
370 sess.err(&format!("the linked panic runtime `{}` is \
371 not compiled with this crate's \
372 panic strategy `{}`",
373 tcx.crate_name(cnum),
374 desired_strategy.desc()));
377 // Next up, verify that all other crates are compatible with this panic
378 // strategy. If the dep isn't linked, we ignore it, and if our strategy
379 // is abort then it's compatible with everything. Otherwise all crates'
380 // panic strategy must match our own.
381 for (i, linkage) in list.iter().enumerate() {
382 if let Linkage::NotLinked = *linkage {
385 if desired_strategy == PanicStrategy::Abort {
388 let cnum = CrateNum::new(i + 1);
389 let found_strategy = tcx.panic_strategy(cnum);
390 let is_compiler_builtins = tcx.is_compiler_builtins(cnum);
391 if is_compiler_builtins || desired_strategy == found_strategy {
395 sess.err(&format!("the crate `{}` is compiled with the \
396 panic strategy `{}` which is \
397 incompatible with this crate's \
399 tcx.crate_name(cnum),
400 found_strategy.desc(),
401 desired_strategy.desc()));