| //! Resolution of mixing rlibs and dylibs |
| //! |
| //! When producing a final artifact, such as a dynamic library, the compiler has |
| //! a choice between linking an rlib or linking a dylib of all upstream |
| //! dependencies. The linking phase must guarantee, however, that a library only |
| //! show up once in the object file. For example, it is illegal for library A to |
| //! be statically linked to B and C in separate dylibs, and then link B and C |
| //! into a crate D (because library A appears twice). |
| //! |
| //! The job of this module is to calculate what format each upstream crate |
| //! should be used when linking each output type requested in this session. This |
| //! generally follows this set of rules: |
| //! |
| //! 1. Each library must appear exactly once in the output. |
| //! 2. Each rlib contains only one library (it's just an object file) |
| //! 3. Each dylib can contain more than one library (due to static linking), |
| //! and can also bring in many dynamic dependencies. |
| //! |
| //! With these constraints in mind, it's generally a very difficult problem to |
| //! find a solution that's not "all rlibs" or "all dylibs". I have suspicions |
| //! that NP-ness may come into the picture here... |
| //! |
| //! The current selection algorithm below looks mostly similar to: |
| //! |
| //! 1. If static linking is required, then require all upstream dependencies |
| //! to be available as rlibs. If not, generate an error. |
| //! 2. If static linking is requested (generating an executable), then |
| //! attempt to use all upstream dependencies as rlibs. If any are not |
| //! found, bail out and continue to step 3. |
| //! 3. Static linking has failed, at least one library must be dynamically |
| //! linked. Apply a heuristic by greedily maximizing the number of |
| //! dynamically linked libraries. |
| //! 4. Each upstream dependency available as a dynamic library is |
| //! registered. The dependencies all propagate, adding to a map. It is |
| //! possible for a dylib to add a static library as a dependency, but it |
| //! is illegal for two dylibs to add the same static library as a |
| //! dependency. The same dylib can be added twice. Additionally, it is |
| //! illegal to add a static dependency when it was previously found as a |
| //! dylib (and vice versa) |
| //! 5. After all dynamic dependencies have been traversed, re-traverse the |
| //! remaining dependencies and add them statically (if they haven't been |
| //! added already). |
| //! |
| //! While not perfect, this algorithm should help support use-cases such as leaf |
| //! dependencies being static while the larger tree of inner dependencies are |
| //! all dynamic. This isn't currently very well battle tested, so it will likely |
| //! fall short in some use cases. |
| //! |
| //! Currently, there is no way to specify the preference of linkage with a |
| //! particular library (other than a global dynamic/static switch). |
| //! Additionally, the algorithm is geared towards finding *any* solution rather |
| //! than finding a number of solutions (there are normally quite a few). |
| |
| use crate::creader::CStore; |
| |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_hir::def_id::CrateNum; |
| use rustc_middle::middle::cstore::LinkagePreference::{self, RequireDynamic, RequireStatic}; |
| use rustc_middle::middle::cstore::{self, DepKind}; |
| use rustc_middle::middle::dependency_format::{Dependencies, DependencyList, Linkage}; |
| use rustc_middle::ty::TyCtxt; |
| use rustc_session::config::CrateType; |
| use rustc_target::spec::PanicStrategy; |
| |
| crate fn calculate(tcx: TyCtxt<'_>) -> Dependencies { |
| tcx.sess |
| .crate_types() |
| .iter() |
| .map(|&ty| { |
| let linkage = calculate_type(tcx, ty); |
| verify_ok(tcx, &linkage); |
| (ty, linkage) |
| }) |
| .collect::<Vec<_>>() |
| } |
| |
| fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList { |
| let sess = &tcx.sess; |
| |
| if !sess.opts.output_types.should_codegen() { |
| return Vec::new(); |
| } |
| |
| let preferred_linkage = match ty { |
| // Generating a dylib without `-C prefer-dynamic` means that we're going |
| // to try to eagerly statically link all dependencies. This is normally |
| // done for end-product dylibs, not intermediate products. |
| // |
| // Treat cdylibs similarly. If `-C prefer-dynamic` is set, the caller may |
| // be code-size conscious, but without it, it makes sense to statically |
| // link a cdylib. |
| CrateType::Dylib | CrateType::Cdylib if !sess.opts.cg.prefer_dynamic => Linkage::Static, |
| CrateType::Dylib | CrateType::Cdylib => Linkage::Dynamic, |
| |
| // If the global prefer_dynamic switch is turned off, or the final |
| // executable will be statically linked, prefer static crate linkage. |
| CrateType::Executable if !sess.opts.cg.prefer_dynamic || sess.crt_static(Some(ty)) => { |
| Linkage::Static |
| } |
| CrateType::Executable => Linkage::Dynamic, |
| |
| // proc-macro crates are mostly cdylibs, but we also need metadata. |
| CrateType::ProcMacro => Linkage::Static, |
| |
| // No linkage happens with rlibs, we just needed the metadata (which we |
| // got long ago), so don't bother with anything. |
| CrateType::Rlib => Linkage::NotLinked, |
| |
| // staticlibs must have all static dependencies. |
| CrateType::Staticlib => Linkage::Static, |
| }; |
| |
| if preferred_linkage == Linkage::NotLinked { |
| // If the crate is not linked, there are no link-time dependencies. |
| return Vec::new(); |
| } |
| |
| if preferred_linkage == Linkage::Static { |
| // Attempt static linkage first. For dylibs and executables, we may be |
| // able to retry below with dynamic linkage. |
| if let Some(v) = attempt_static(tcx) { |
| return v; |
| } |
| |
| // Staticlibs and static executables must have all static dependencies. |
| // If any are not found, generate some nice pretty errors. |
| if ty == CrateType::Staticlib |
| || (ty == CrateType::Executable |
| && sess.crt_static(Some(ty)) |
| && !sess.target.target.options.crt_static_allows_dylibs) |
| { |
| for &cnum in tcx.crates().iter() { |
| if tcx.dep_kind(cnum).macros_only() { |
| continue; |
| } |
| let src = tcx.used_crate_source(cnum); |
| if src.rlib.is_some() { |
| continue; |
| } |
| sess.err(&format!( |
| "crate `{}` required to be available in rlib format, \ |
| but was not found in this form", |
| tcx.crate_name(cnum) |
| )); |
| } |
| return Vec::new(); |
| } |
| } |
| |
| let mut formats = FxHashMap::default(); |
| |
| // Sweep all crates for found dylibs. Add all dylibs, as well as their |
| // dependencies, ensuring there are no conflicts. The only valid case for a |
| // dependency to be relied upon twice is for both cases to rely on a dylib. |
| for &cnum in tcx.crates().iter() { |
| if tcx.dep_kind(cnum).macros_only() { |
| continue; |
| } |
| let name = tcx.crate_name(cnum); |
| let src = tcx.used_crate_source(cnum); |
| if src.dylib.is_some() { |
| log::info!("adding dylib: {}", name); |
| add_library(tcx, cnum, RequireDynamic, &mut formats); |
| let deps = tcx.dylib_dependency_formats(cnum); |
| for &(depnum, style) in deps.iter() { |
| log::info!("adding {:?}: {}", style, tcx.crate_name(depnum)); |
| add_library(tcx, depnum, style, &mut formats); |
| } |
| } |
| } |
| |
| // Collect what we've got so far in the return vector. |
| let last_crate = tcx.crates().len(); |
| let mut ret = (1..last_crate + 1) |
| .map(|cnum| match formats.get(&CrateNum::new(cnum)) { |
| Some(&RequireDynamic) => Linkage::Dynamic, |
| Some(&RequireStatic) => Linkage::IncludedFromDylib, |
| None => Linkage::NotLinked, |
| }) |
| .collect::<Vec<_>>(); |
| |
| // Run through the dependency list again, and add any missing libraries as |
| // static libraries. |
| // |
| // If the crate hasn't been included yet and it's not actually required |
| // (e.g., it's an allocator) then we skip it here as well. |
| for &cnum in tcx.crates().iter() { |
| let src = tcx.used_crate_source(cnum); |
| if src.dylib.is_none() |
| && !formats.contains_key(&cnum) |
| && tcx.dep_kind(cnum) == DepKind::Explicit |
| { |
| assert!(src.rlib.is_some() || src.rmeta.is_some()); |
| log::info!("adding staticlib: {}", tcx.crate_name(cnum)); |
| add_library(tcx, cnum, RequireStatic, &mut formats); |
| ret[cnum.as_usize() - 1] = Linkage::Static; |
| } |
| } |
| |
| // We've gotten this far because we're emitting some form of a final |
| // artifact which means that we may need to inject dependencies of some |
| // form. |
| // |
| // Things like allocators and panic runtimes may not have been activated |
| // quite yet, so do so here. |
| activate_injected_dep(CStore::from_tcx(tcx).injected_panic_runtime(), &mut ret, &|cnum| { |
| tcx.is_panic_runtime(cnum) |
| }); |
| |
| // When dylib B links to dylib A, then when using B we must also link to A. |
| // It could be the case, however, that the rlib for A is present (hence we |
| // found metadata), but the dylib for A has since been removed. |
| // |
| // For situations like this, we perform one last pass over the dependencies, |
| // making sure that everything is available in the requested format. |
| for (cnum, kind) in ret.iter().enumerate() { |
| let cnum = CrateNum::new(cnum + 1); |
| let src = tcx.used_crate_source(cnum); |
| match *kind { |
| Linkage::NotLinked | Linkage::IncludedFromDylib => {} |
| Linkage::Static if src.rlib.is_some() => continue, |
| Linkage::Dynamic if src.dylib.is_some() => continue, |
| kind => { |
| let kind = match kind { |
| Linkage::Static => "rlib", |
| _ => "dylib", |
| }; |
| sess.err(&format!( |
| "crate `{}` required to be available in {} format, \ |
| but was not found in this form", |
| tcx.crate_name(cnum), |
| kind |
| )); |
| } |
| } |
| } |
| |
| ret |
| } |
| |
| fn add_library( |
| tcx: TyCtxt<'_>, |
| cnum: CrateNum, |
| link: LinkagePreference, |
| m: &mut FxHashMap<CrateNum, LinkagePreference>, |
| ) { |
| match m.get(&cnum) { |
| Some(&link2) => { |
| // If the linkages differ, then we'd have two copies of the library |
| // if we continued linking. If the linkages are both static, then we |
| // would also have two copies of the library (static from two |
| // different locations). |
| // |
| // This error is probably a little obscure, but I imagine that it |
| // can be refined over time. |
| if link2 != link || link == RequireStatic { |
| tcx.sess |
| .struct_err(&format!( |
| "cannot satisfy dependencies so `{}` only \ |
| shows up once", |
| tcx.crate_name(cnum) |
| )) |
| .help( |
| "having upstream crates all available in one format \ |
| will likely make this go away", |
| ) |
| .emit(); |
| } |
| } |
| None => { |
| m.insert(cnum, link); |
| } |
| } |
| } |
| |
| fn attempt_static(tcx: TyCtxt<'_>) -> Option<DependencyList> { |
| let crates = cstore::used_crates(tcx, RequireStatic); |
| if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) { |
| return None; |
| } |
| |
| // All crates are available in an rlib format, so we're just going to link |
| // everything in explicitly so long as it's actually required. |
| let last_crate = tcx.crates().len(); |
| let mut ret = (1..last_crate + 1) |
| .map(|cnum| { |
| if tcx.dep_kind(CrateNum::new(cnum)) == DepKind::Explicit { |
| Linkage::Static |
| } else { |
| Linkage::NotLinked |
| } |
| }) |
| .collect::<Vec<_>>(); |
| |
| // Our allocator/panic runtime may not have been linked above if it wasn't |
| // explicitly linked, which is the case for any injected dependency. Handle |
| // that here and activate them. |
| activate_injected_dep(CStore::from_tcx(tcx).injected_panic_runtime(), &mut ret, &|cnum| { |
| tcx.is_panic_runtime(cnum) |
| }); |
| |
| Some(ret) |
| } |
| |
| // Given a list of how to link upstream dependencies so far, ensure that an |
| // injected dependency is activated. This will not do anything if one was |
| // transitively included already (e.g., via a dylib or explicitly so). |
| // |
| // If an injected dependency was not found then we're guaranteed the |
| // metadata::creader module has injected that dependency (not listed as |
| // a required dependency) in one of the session's field. If this field is not |
| // set then this compilation doesn't actually need the dependency and we can |
| // also skip this step entirely. |
| fn activate_injected_dep( |
| injected: Option<CrateNum>, |
| list: &mut DependencyList, |
| replaces_injected: &dyn Fn(CrateNum) -> bool, |
| ) { |
| for (i, slot) in list.iter().enumerate() { |
| let cnum = CrateNum::new(i + 1); |
| if !replaces_injected(cnum) { |
| continue; |
| } |
| if *slot != Linkage::NotLinked { |
| return; |
| } |
| } |
| if let Some(injected) = injected { |
| let idx = injected.as_usize() - 1; |
| assert_eq!(list[idx], Linkage::NotLinked); |
| list[idx] = Linkage::Static; |
| } |
| } |
| |
| // After the linkage for a crate has been determined we need to verify that |
| // there's only going to be one allocator in the output. |
| fn verify_ok(tcx: TyCtxt<'_>, list: &[Linkage]) { |
| let sess = &tcx.sess; |
| if list.is_empty() { |
| return; |
| } |
| let mut panic_runtime = None; |
| for (i, linkage) in list.iter().enumerate() { |
| if let Linkage::NotLinked = *linkage { |
| continue; |
| } |
| let cnum = CrateNum::new(i + 1); |
| |
| if tcx.is_panic_runtime(cnum) { |
| if let Some((prev, _)) = panic_runtime { |
| let prev_name = tcx.crate_name(prev); |
| let cur_name = tcx.crate_name(cnum); |
| sess.err(&format!( |
| "cannot link together two \ |
| panic runtimes: {} and {}", |
| prev_name, cur_name |
| )); |
| } |
| panic_runtime = Some((cnum, tcx.panic_strategy(cnum))); |
| } |
| } |
| |
| // If we found a panic runtime, then we know by this point that it's the |
| // only one, but we perform validation here that all the panic strategy |
| // compilation modes for the whole DAG are valid. |
| if let Some((cnum, found_strategy)) = panic_runtime { |
| let desired_strategy = sess.panic_strategy(); |
| |
| // First up, validate that our selected panic runtime is indeed exactly |
| // our same strategy. |
| if found_strategy != desired_strategy { |
| sess.err(&format!( |
| "the linked panic runtime `{}` is \ |
| not compiled with this crate's \ |
| panic strategy `{}`", |
| tcx.crate_name(cnum), |
| desired_strategy.desc() |
| )); |
| } |
| |
| // Next up, verify that all other crates are compatible with this panic |
| // strategy. If the dep isn't linked, we ignore it, and if our strategy |
| // is abort then it's compatible with everything. Otherwise all crates' |
| // panic strategy must match our own. |
| for (i, linkage) in list.iter().enumerate() { |
| if let Linkage::NotLinked = *linkage { |
| continue; |
| } |
| if desired_strategy == PanicStrategy::Abort { |
| continue; |
| } |
| let cnum = CrateNum::new(i + 1); |
| let found_strategy = tcx.panic_strategy(cnum); |
| let is_compiler_builtins = tcx.is_compiler_builtins(cnum); |
| if is_compiler_builtins || desired_strategy == found_strategy { |
| continue; |
| } |
| |
| sess.err(&format!( |
| "the crate `{}` is compiled with the \ |
| panic strategy `{}` which is \ |
| incompatible with this crate's \ |
| strategy of `{}`", |
| tcx.crate_name(cnum), |
| found_strategy.desc(), |
| desired_strategy.desc() |
| )); |
| } |
| } |
| } |
