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 rustc::hir::def_id::CrateNum;
55 use rustc::middle::cstore::LinkagePreference::{self, RequireStatic, RequireDynamic};
56 use rustc::middle::cstore::{self, DepKind};
57 use rustc::middle::dependency_format::{DependencyList, Dependencies, Linkage};
58 use rustc::session::config;
59 use rustc::ty::TyCtxt;
60 use rustc::util::nodemap::FxHashMap;
61 use rustc_target::spec::PanicStrategy;
63 crate fn calculate(tcx: TyCtxt<'_>) -> Dependencies {
64 tcx.sess.crate_types.borrow().iter().map(|&ty| {
65 let linkage = calculate_type(tcx, ty);
66 verify_ok(tcx, &linkage);
68 }).collect::<Vec<_>>()
71 fn calculate_type(tcx: TyCtxt<'_>, ty: config::CrateType) -> DependencyList {
74 if !sess.opts.output_types.should_codegen() {
78 let preferred_linkage = match ty {
79 // cdylibs must have all static dependencies.
80 config::CrateType::Cdylib => Linkage::Static,
82 // Generating a dylib without `-C prefer-dynamic` means that we're going
83 // to try to eagerly statically link all dependencies. This is normally
84 // done for end-product dylibs, not intermediate products.
85 config::CrateType::Dylib if !sess.opts.cg.prefer_dynamic => Linkage::Static,
86 config::CrateType::Dylib => Linkage::Dynamic,
88 // If the global prefer_dynamic switch is turned off, or the final
89 // executable will be statically linked, prefer static crate linkage.
90 config::CrateType::Executable if !sess.opts.cg.prefer_dynamic ||
91 sess.crt_static() => Linkage::Static,
92 config::CrateType::Executable => Linkage::Dynamic,
94 // proc-macro crates are mostly cdylibs, but we also need metadata.
95 config::CrateType::ProcMacro => Linkage::Static,
97 // No linkage happens with rlibs, we just needed the metadata (which we
98 // got long ago), so don't bother with anything.
99 config::CrateType::Rlib => Linkage::NotLinked,
101 // staticlibs must have all static dependencies.
102 config::CrateType::Staticlib => Linkage::Static,
105 if preferred_linkage == Linkage::NotLinked {
106 // If the crate is not linked, there are no link-time dependencies.
110 if preferred_linkage == Linkage::Static {
111 // Attempt static linkage first. For dylibs and executables, we may be
112 // able to retry below with dynamic linkage.
113 if let Some(v) = attempt_static(tcx) {
117 // Staticlibs, cdylibs, and static executables must have all static
118 // dependencies. If any are not found, generate some nice pretty errors.
119 if ty == config::CrateType::Cdylib || ty == config::CrateType::Staticlib ||
120 (ty == config::CrateType::Executable && sess.crt_static() &&
121 !sess.target.target.options.crt_static_allows_dylibs) {
122 for &cnum in tcx.crates().iter() {
123 if tcx.dep_kind(cnum).macros_only() { continue }
124 let src = tcx.used_crate_source(cnum);
125 if src.rlib.is_some() { continue }
126 sess.err(&format!("crate `{}` required to be available in rlib format, \
127 but was not found in this form",
128 tcx.crate_name(cnum)));
134 let mut formats = FxHashMap::default();
136 // Sweep all crates for found dylibs. Add all dylibs, as well as their
137 // dependencies, ensuring there are no conflicts. The only valid case for a
138 // dependency to be relied upon twice is for both cases to rely on a dylib.
139 for &cnum in tcx.crates().iter() {
140 if tcx.dep_kind(cnum).macros_only() { continue }
141 let name = tcx.crate_name(cnum);
142 let src = tcx.used_crate_source(cnum);
143 if src.dylib.is_some() {
144 log::info!("adding dylib: {}", name);
145 add_library(tcx, cnum, RequireDynamic, &mut formats);
146 let deps = tcx.dylib_dependency_formats(cnum);
147 for &(depnum, style) in deps.iter() {
148 log::info!("adding {:?}: {}", style, tcx.crate_name(depnum));
149 add_library(tcx, depnum, style, &mut formats);
154 // Collect what we've got so far in the return vector.
155 let last_crate = tcx.crates().len();
156 let mut ret = (1..last_crate+1).map(|cnum| {
157 match formats.get(&CrateNum::new(cnum)) {
158 Some(&RequireDynamic) => Linkage::Dynamic,
159 Some(&RequireStatic) => Linkage::IncludedFromDylib,
160 None => Linkage::NotLinked,
162 }).collect::<Vec<_>>();
164 // Run through the dependency list again, and add any missing libraries as
167 // If the crate hasn't been included yet and it's not actually required
168 // (e.g., it's an allocator) then we skip it here as well.
169 for &cnum in tcx.crates().iter() {
170 let src = tcx.used_crate_source(cnum);
171 if src.dylib.is_none() &&
172 !formats.contains_key(&cnum) &&
173 tcx.dep_kind(cnum) == DepKind::Explicit {
174 assert!(src.rlib.is_some() || src.rmeta.is_some());
175 log::info!("adding staticlib: {}", tcx.crate_name(cnum));
176 add_library(tcx, cnum, RequireStatic, &mut formats);
177 ret[cnum.as_usize() - 1] = Linkage::Static;
181 // We've gotten this far because we're emitting some form of a final
182 // artifact which means that we may need to inject dependencies of some
185 // Things like allocators and panic runtimes may not have been activated
186 // quite yet, so do so here.
187 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
188 &|cnum| tcx.is_panic_runtime(cnum));
190 // When dylib B links to dylib A, then when using B we must also link to A.
191 // It could be the case, however, that the rlib for A is present (hence we
192 // found metadata), but the dylib for A has since been removed.
194 // For situations like this, we perform one last pass over the dependencies,
195 // making sure that everything is available in the requested format.
196 for (cnum, kind) in ret.iter().enumerate() {
197 let cnum = CrateNum::new(cnum + 1);
198 let src = tcx.used_crate_source(cnum);
201 Linkage::IncludedFromDylib => {}
202 Linkage::Static if src.rlib.is_some() => continue,
203 Linkage::Dynamic if src.dylib.is_some() => continue,
205 let kind = match kind {
206 Linkage::Static => "rlib",
209 sess.err(&format!("crate `{}` required to be available in {} format, \
210 but was not found in this form",
211 tcx.crate_name(cnum), kind));
222 link: LinkagePreference,
223 m: &mut FxHashMap<CrateNum, LinkagePreference>,
227 // If the linkages differ, then we'd have two copies of the library
228 // if we continued linking. If the linkages are both static, then we
229 // would also have two copies of the library (static from two
230 // different locations).
232 // This error is probably a little obscure, but I imagine that it
233 // can be refined over time.
234 if link2 != link || link == RequireStatic {
235 tcx.sess.struct_err(&format!("cannot satisfy dependencies so `{}` only \
236 shows up once", tcx.crate_name(cnum)))
237 .help("having upstream crates all available in one format \
238 will likely make this go away")
242 None => { m.insert(cnum, link); }
246 fn attempt_static(tcx: TyCtxt<'_>) -> Option<DependencyList> {
247 let sess = &tcx.sess;
248 let crates = cstore::used_crates(tcx, RequireStatic);
249 if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) {
253 // All crates are available in an rlib format, so we're just going to link
254 // everything in explicitly so long as it's actually required.
255 let last_crate = tcx.crates().len();
256 let mut ret = (1..last_crate+1).map(|cnum| {
257 if tcx.dep_kind(CrateNum::new(cnum)) == DepKind::Explicit {
262 }).collect::<Vec<_>>();
264 // Our allocator/panic runtime may not have been linked above if it wasn't
265 // explicitly linked, which is the case for any injected dependency. Handle
266 // that here and activate them.
267 activate_injected_dep(*sess.injected_panic_runtime.get(), &mut ret,
268 &|cnum| tcx.is_panic_runtime(cnum));
273 // Given a list of how to link upstream dependencies so far, ensure that an
274 // injected dependency is activated. This will not do anything if one was
275 // transitively included already (e.g., via a dylib or explicitly so).
277 // If an injected dependency was not found then we're guaranteed the
278 // metadata::creader module has injected that dependency (not listed as
279 // a required dependency) in one of the session's field. If this field is not
280 // set then this compilation doesn't actually need the dependency and we can
281 // also skip this step entirely.
282 fn activate_injected_dep(injected: Option<CrateNum>,
283 list: &mut DependencyList,
284 replaces_injected: &dyn Fn(CrateNum) -> bool) {
285 for (i, slot) in list.iter().enumerate() {
286 let cnum = CrateNum::new(i + 1);
287 if !replaces_injected(cnum) {
290 if *slot != Linkage::NotLinked {
294 if let Some(injected) = injected {
295 let idx = injected.as_usize() - 1;
296 assert_eq!(list[idx], Linkage::NotLinked);
297 list[idx] = Linkage::Static;
301 // After the linkage for a crate has been determined we need to verify that
302 // there's only going to be one allocator in the output.
303 fn verify_ok(tcx: TyCtxt<'_>, list: &[Linkage]) {
304 let sess = &tcx.sess;
308 let mut panic_runtime = None;
309 for (i, linkage) in list.iter().enumerate() {
310 if let Linkage::NotLinked = *linkage {
313 let cnum = CrateNum::new(i + 1);
315 if tcx.is_panic_runtime(cnum) {
316 if let Some((prev, _)) = panic_runtime {
317 let prev_name = tcx.crate_name(prev);
318 let cur_name = tcx.crate_name(cnum);
319 sess.err(&format!("cannot link together two \
320 panic runtimes: {} and {}",
321 prev_name, cur_name));
323 panic_runtime = Some((cnum, tcx.panic_strategy(cnum)));
327 // If we found a panic runtime, then we know by this point that it's the
328 // only one, but we perform validation here that all the panic strategy
329 // compilation modes for the whole DAG are valid.
330 if let Some((cnum, found_strategy)) = panic_runtime {
331 let desired_strategy = sess.panic_strategy();
333 // First up, validate that our selected panic runtime is indeed exactly
334 // our same strategy.
335 if found_strategy != desired_strategy {
336 sess.err(&format!("the linked panic runtime `{}` is \
337 not compiled with this crate's \
338 panic strategy `{}`",
339 tcx.crate_name(cnum),
340 desired_strategy.desc()));
343 // Next up, verify that all other crates are compatible with this panic
344 // strategy. If the dep isn't linked, we ignore it, and if our strategy
345 // is abort then it's compatible with everything. Otherwise all crates'
346 // panic strategy must match our own.
347 for (i, linkage) in list.iter().enumerate() {
348 if let Linkage::NotLinked = *linkage {
351 if desired_strategy == PanicStrategy::Abort {
354 let cnum = CrateNum::new(i + 1);
355 let found_strategy = tcx.panic_strategy(cnum);
356 let is_compiler_builtins = tcx.is_compiler_builtins(cnum);
357 if is_compiler_builtins || desired_strategy == found_strategy {
361 sess.err(&format!("the crate `{}` is compiled with the \
362 panic strategy `{}` which is \
363 incompatible with this crate's \
365 tcx.crate_name(cnum),
366 found_strategy.desc(),
367 desired_strategy.desc()));