1 //! Resolution of mixing rlibs and dylibs
3 //! When producing a final artifact, such as a dynamic library, the compiler has
4 //! a choice between linking an rlib or linking a dylib of all upstream
5 //! dependencies. The linking phase must guarantee, however, that a library only
6 //! show up once in the object file. For example, it is illegal for library A to
7 //! be statically linked to B and C in separate dylibs, and then link B and C
8 //! into a crate D (because library A appears twice).
10 //! The job of this module is to calculate what format each upstream crate
11 //! should be used when linking each output type requested in this session. This
12 //! generally follows this set of rules:
14 //! 1. Each library must appear exactly once in the output.
15 //! 2. Each rlib contains only one library (it's just an object file)
16 //! 3. Each dylib can contain more than one library (due to static linking),
17 //! and can also bring in many dynamic dependencies.
19 //! With these constraints in mind, it's generally a very difficult problem to
20 //! find a solution that's not "all rlibs" or "all dylibs". I have suspicions
21 //! that NP-ness may come into the picture here...
23 //! The current selection algorithm below looks mostly similar to:
25 //! 1. If static linking is required, then require all upstream dependencies
26 //! to be available as rlibs. If not, generate an error.
27 //! 2. If static linking is requested (generating an executable), then
28 //! attempt to use all upstream dependencies as rlibs. If any are not
29 //! found, bail out and continue to step 3.
30 //! 3. Static linking has failed, at least one library must be dynamically
31 //! linked. Apply a heuristic by greedily maximizing the number of
32 //! dynamically linked libraries.
33 //! 4. Each upstream dependency available as a dynamic library is
34 //! registered. The dependencies all propagate, adding to a map. It is
35 //! possible for a dylib to add a static library as a dependency, but it
36 //! is illegal for two dylibs to add the same static library as a
37 //! dependency. The same dylib can be added twice. Additionally, it is
38 //! illegal to add a static dependency when it was previously found as a
39 //! dylib (and vice versa)
40 //! 5. After all dynamic dependencies have been traversed, re-traverse the
41 //! remaining dependencies and add them statically (if they haven't been
44 //! While not perfect, this algorithm should help support use-cases such as leaf
45 //! dependencies being static while the larger tree of inner dependencies are
46 //! all dynamic. This isn't currently very well battle tested, so it will likely
47 //! fall short in some use cases.
49 //! Currently, there is no way to specify the preference of linkage with a
50 //! particular library (other than a global dynamic/static switch).
51 //! Additionally, the algorithm is geared towards finding *any* solution rather
52 //! than finding a number of solutions (there are normally quite a few).
54 use crate::creader::CStore;
56 use rustc::hir::def_id::CrateNum;
57 use rustc::middle::cstore::LinkagePreference::{self, RequireDynamic, RequireStatic};
58 use rustc::middle::cstore::{self, DepKind};
59 use rustc::middle::dependency_format::{Dependencies, DependencyList, Linkage};
60 use rustc::session::config;
61 use rustc::ty::TyCtxt;
62 use rustc_data_structures::fx::FxHashMap;
63 use rustc_target::spec::PanicStrategy;
65 crate fn calculate(tcx: TyCtxt<'_>) -> Dependencies {
71 let linkage = calculate_type(tcx, ty);
72 verify_ok(tcx, &linkage);
78 fn calculate_type(tcx: TyCtxt<'_>, ty: config::CrateType) -> DependencyList {
81 if !sess.opts.output_types.should_codegen() {
85 let preferred_linkage = match ty {
86 // cdylibs must have all static dependencies.
87 config::CrateType::Cdylib => Linkage::Static,
89 // Generating a dylib without `-C prefer-dynamic` means that we're going
90 // to try to eagerly statically link all dependencies. This is normally
91 // done for end-product dylibs, not intermediate products.
92 config::CrateType::Dylib if !sess.opts.cg.prefer_dynamic => Linkage::Static,
93 config::CrateType::Dylib => Linkage::Dynamic,
95 // If the global prefer_dynamic switch is turned off, or the final
96 // executable will be statically linked, prefer static crate linkage.
97 config::CrateType::Executable if !sess.opts.cg.prefer_dynamic || sess.crt_static() => {
100 config::CrateType::Executable => Linkage::Dynamic,
102 // proc-macro crates are mostly cdylibs, but we also need metadata.
103 config::CrateType::ProcMacro => Linkage::Static,
105 // No linkage happens with rlibs, we just needed the metadata (which we
106 // got long ago), so don't bother with anything.
107 config::CrateType::Rlib => Linkage::NotLinked,
109 // staticlibs must have all static dependencies.
110 config::CrateType::Staticlib => Linkage::Static,
113 if preferred_linkage == Linkage::NotLinked {
114 // If the crate is not linked, there are no link-time dependencies.
118 if preferred_linkage == Linkage::Static {
119 // Attempt static linkage first. For dylibs and executables, we may be
120 // able to retry below with dynamic linkage.
121 if let Some(v) = attempt_static(tcx) {
125 // Staticlibs, cdylibs, and static executables must have all static
126 // dependencies. If any are not found, generate some nice pretty errors.
127 if ty == config::CrateType::Cdylib
128 || ty == config::CrateType::Staticlib
129 || (ty == config::CrateType::Executable
131 && !sess.target.target.options.crt_static_allows_dylibs)
133 for &cnum in tcx.crates().iter() {
134 if tcx.dep_kind(cnum).macros_only() {
137 let src = tcx.used_crate_source(cnum);
138 if src.rlib.is_some() {
142 "crate `{}` required to be available in rlib format, \
143 but was not found in this form",
151 let mut formats = FxHashMap::default();
153 // Sweep all crates for found dylibs. Add all dylibs, as well as their
154 // dependencies, ensuring there are no conflicts. The only valid case for a
155 // dependency to be relied upon twice is for both cases to rely on a dylib.
156 for &cnum in tcx.crates().iter() {
157 if tcx.dep_kind(cnum).macros_only() {
160 let name = tcx.crate_name(cnum);
161 let src = tcx.used_crate_source(cnum);
162 if src.dylib.is_some() {
163 log::info!("adding dylib: {}", name);
164 add_library(tcx, cnum, RequireDynamic, &mut formats);
165 let deps = tcx.dylib_dependency_formats(cnum);
166 for &(depnum, style) in deps.iter() {
167 log::info!("adding {:?}: {}", style, tcx.crate_name(depnum));
168 add_library(tcx, depnum, style, &mut formats);
173 // Collect what we've got so far in the return vector.
174 let last_crate = tcx.crates().len();
175 let mut ret = (1..last_crate + 1)
176 .map(|cnum| match formats.get(&CrateNum::new(cnum)) {
177 Some(&RequireDynamic) => Linkage::Dynamic,
178 Some(&RequireStatic) => Linkage::IncludedFromDylib,
179 None => Linkage::NotLinked,
181 .collect::<Vec<_>>();
183 // Run through the dependency list again, and add any missing libraries as
186 // If the crate hasn't been included yet and it's not actually required
187 // (e.g., it's an allocator) then we skip it here as well.
188 for &cnum in tcx.crates().iter() {
189 let src = tcx.used_crate_source(cnum);
190 if src.dylib.is_none()
191 && !formats.contains_key(&cnum)
192 && tcx.dep_kind(cnum) == DepKind::Explicit
194 assert!(src.rlib.is_some() || src.rmeta.is_some());
195 log::info!("adding staticlib: {}", tcx.crate_name(cnum));
196 add_library(tcx, cnum, RequireStatic, &mut formats);
197 ret[cnum.as_usize() - 1] = Linkage::Static;
201 // We've gotten this far because we're emitting some form of a final
202 // artifact which means that we may need to inject dependencies of some
205 // Things like allocators and panic runtimes may not have been activated
206 // quite yet, so do so here.
207 activate_injected_dep(CStore::from_tcx(tcx).injected_panic_runtime(), &mut ret, &|cnum| {
208 tcx.is_panic_runtime(cnum)
211 // When dylib B links to dylib A, then when using B we must also link to A.
212 // It could be the case, however, that the rlib for A is present (hence we
213 // found metadata), but the dylib for A has since been removed.
215 // For situations like this, we perform one last pass over the dependencies,
216 // making sure that everything is available in the requested format.
217 for (cnum, kind) in ret.iter().enumerate() {
218 let cnum = CrateNum::new(cnum + 1);
219 let src = tcx.used_crate_source(cnum);
221 Linkage::NotLinked | Linkage::IncludedFromDylib => {}
222 Linkage::Static if src.rlib.is_some() => continue,
223 Linkage::Dynamic if src.dylib.is_some() => continue,
225 let kind = match kind {
226 Linkage::Static => "rlib",
230 "crate `{}` required to be available in {} format, \
231 but was not found in this form",
232 tcx.crate_name(cnum),
245 link: LinkagePreference,
246 m: &mut FxHashMap<CrateNum, LinkagePreference>,
250 // If the linkages differ, then we'd have two copies of the library
251 // if we continued linking. If the linkages are both static, then we
252 // would also have two copies of the library (static from two
253 // different locations).
255 // This error is probably a little obscure, but I imagine that it
256 // can be refined over time.
257 if link2 != link || link == RequireStatic {
259 .struct_err(&format!(
260 "cannot satisfy dependencies so `{}` only \
265 "having upstream crates all available in one format \
266 will likely make this go away",
272 m.insert(cnum, link);
277 fn attempt_static(tcx: TyCtxt<'_>) -> Option<DependencyList> {
278 let crates = cstore::used_crates(tcx, RequireStatic);
279 if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) {
283 // All crates are available in an rlib format, so we're just going to link
284 // everything in explicitly so long as it's actually required.
285 let last_crate = tcx.crates().len();
286 let mut ret = (1..last_crate + 1)
288 if tcx.dep_kind(CrateNum::new(cnum)) == DepKind::Explicit {
294 .collect::<Vec<_>>();
296 // Our allocator/panic runtime may not have been linked above if it wasn't
297 // explicitly linked, which is the case for any injected dependency. Handle
298 // that here and activate them.
299 activate_injected_dep(CStore::from_tcx(tcx).injected_panic_runtime(), &mut ret, &|cnum| {
300 tcx.is_panic_runtime(cnum)
306 // Given a list of how to link upstream dependencies so far, ensure that an
307 // injected dependency is activated. This will not do anything if one was
308 // transitively included already (e.g., via a dylib or explicitly so).
310 // If an injected dependency was not found then we're guaranteed the
311 // metadata::creader module has injected that dependency (not listed as
312 // a required dependency) in one of the session's field. If this field is not
313 // set then this compilation doesn't actually need the dependency and we can
314 // also skip this step entirely.
315 fn activate_injected_dep(
316 injected: Option<CrateNum>,
317 list: &mut DependencyList,
318 replaces_injected: &dyn Fn(CrateNum) -> bool,
320 for (i, slot) in list.iter().enumerate() {
321 let cnum = CrateNum::new(i + 1);
322 if !replaces_injected(cnum) {
325 if *slot != Linkage::NotLinked {
329 if let Some(injected) = injected {
330 let idx = injected.as_usize() - 1;
331 assert_eq!(list[idx], Linkage::NotLinked);
332 list[idx] = Linkage::Static;
336 // After the linkage for a crate has been determined we need to verify that
337 // there's only going to be one allocator in the output.
338 fn verify_ok(tcx: TyCtxt<'_>, list: &[Linkage]) {
339 let sess = &tcx.sess;
343 let mut panic_runtime = None;
344 for (i, linkage) in list.iter().enumerate() {
345 if let Linkage::NotLinked = *linkage {
348 let cnum = CrateNum::new(i + 1);
350 if tcx.is_panic_runtime(cnum) {
351 if let Some((prev, _)) = panic_runtime {
352 let prev_name = tcx.crate_name(prev);
353 let cur_name = tcx.crate_name(cnum);
355 "cannot link together two \
356 panic runtimes: {} and {}",
360 panic_runtime = Some((cnum, tcx.panic_strategy(cnum)));
364 // If we found a panic runtime, then we know by this point that it's the
365 // only one, but we perform validation here that all the panic strategy
366 // compilation modes for the whole DAG are valid.
367 if let Some((cnum, found_strategy)) = panic_runtime {
368 let desired_strategy = sess.panic_strategy();
370 // First up, validate that our selected panic runtime is indeed exactly
371 // our same strategy.
372 if found_strategy != desired_strategy {
374 "the linked panic runtime `{}` is \
375 not compiled with this crate's \
376 panic strategy `{}`",
377 tcx.crate_name(cnum),
378 desired_strategy.desc()
382 // Next up, verify that all other crates are compatible with this panic
383 // strategy. If the dep isn't linked, we ignore it, and if our strategy
384 // is abort then it's compatible with everything. Otherwise all crates'
385 // panic strategy must match our own.
386 for (i, linkage) in list.iter().enumerate() {
387 if let Linkage::NotLinked = *linkage {
390 if desired_strategy == PanicStrategy::Abort {
393 let cnum = CrateNum::new(i + 1);
394 let found_strategy = tcx.panic_strategy(cnum);
395 let is_compiler_builtins = tcx.is_compiler_builtins(cnum);
396 if is_compiler_builtins || desired_strategy == found_strategy {
401 "the crate `{}` is compiled with the \
402 panic strategy `{}` which is \
403 incompatible with this crate's \
405 tcx.crate_name(cnum),
406 found_strategy.desc(),
407 desired_strategy.desc()