336 lines
14 KiB
Rust
336 lines
14 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Resolution of mixing rlibs and dylibs
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//!
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//! When producing a final artifact, such as a dynamic library, the compiler has
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//! a choice between linking an rlib or linking a dylib of all upstream
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//! dependencies. The linking phase must guarantee, however, that a library only
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//! show up once in the object file. For example, it is illegal for library A to
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//! be statically linked to B and C in separate dylibs, and then link B and C
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//! into a crate D (because library A appears twice).
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//!
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//! The job of this module is to calculate what format each upstream crate
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//! should be used when linking each output type requested in this session. This
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//! generally follows this set of rules:
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//!
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//! 1. Each library must appear exactly once in the output.
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//! 2. Each rlib contains only one library (it's just an object file)
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//! 3. Each dylib can contain more than one library (due to static linking),
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//! and can also bring in many dynamic dependencies.
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//!
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//! With these constraints in mind, it's generally a very difficult problem to
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//! find a solution that's not "all rlibs" or "all dylibs". I have suspicions
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//! that NP-ness may come into the picture here...
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//!
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//! The current selection algorithm below looks mostly similar to:
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//!
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//! 1. If static linking is required, then require all upstream dependencies
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//! to be available as rlibs. If not, generate an error.
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//! 2. If static linking is requested (generating an executable), then
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//! attempt to use all upstream dependencies as rlibs. If any are not
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//! found, bail out and continue to step 3.
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//! 3. Static linking has failed, at least one library must be dynamically
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//! linked. Apply a heuristic by greedily maximizing the number of
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//! dynamically linked libraries.
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//! 4. Each upstream dependency available as a dynamic library is
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//! registered. The dependencies all propagate, adding to a map. It is
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//! possible for a dylib to add a static library as a dependency, but it
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//! is illegal for two dylibs to add the same static library as a
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//! dependency. The same dylib can be added twice. Additionally, it is
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//! illegal to add a static dependency when it was previously found as a
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//! dylib (and vice versa)
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//! 5. After all dynamic dependencies have been traversed, re-traverse the
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//! remaining dependencies and add them statically (if they haven't been
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//! added already).
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//!
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//! While not perfect, this algorithm should help support use-cases such as leaf
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//! dependencies being static while the larger tree of inner dependencies are
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//! all dynamic. This isn't currently very well battle tested, so it will likely
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//! fall short in some use cases.
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//!
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//! Currently, there is no way to specify the preference of linkage with a
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//! particular library (other than a global dynamic/static switch).
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//! Additionally, the algorithm is geared towards finding *any* solution rather
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//! than finding a number of solutions (there are normally quite a few).
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use syntax::ast;
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use session;
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use session::config;
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use middle::cstore::CrateStore;
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use middle::cstore::LinkagePreference::{self, RequireStatic, RequireDynamic};
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use util::nodemap::FnvHashMap;
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/// A list of dependencies for a certain crate type.
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///
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/// The length of this vector is the same as the number of external crates used.
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/// The value is None if the crate does not need to be linked (it was found
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/// statically in another dylib), or Some(kind) if it needs to be linked as
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/// `kind` (either static or dynamic).
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pub type DependencyList = Vec<Linkage>;
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/// A mapping of all required dependencies for a particular flavor of output.
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///
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/// This is local to the tcx, and is generally relevant to one session.
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pub type Dependencies = FnvHashMap<config::CrateType, DependencyList>;
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#[derive(Copy, Clone, PartialEq, Debug)]
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pub enum Linkage {
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NotLinked,
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IncludedFromDylib,
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Static,
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Dynamic,
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}
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pub fn calculate(sess: &session::Session) {
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let mut fmts = sess.dependency_formats.borrow_mut();
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for &ty in sess.crate_types.borrow().iter() {
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let linkage = calculate_type(sess, ty);
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verify_ok(sess, &linkage);
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fmts.insert(ty, linkage);
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}
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sess.abort_if_errors();
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}
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fn calculate_type(sess: &session::Session,
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ty: config::CrateType) -> DependencyList {
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match ty {
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// If the global prefer_dynamic switch is turned off, first attempt
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// static linkage (this can fail).
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config::CrateTypeExecutable if !sess.opts.cg.prefer_dynamic => {
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match attempt_static(sess) {
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Some(v) => return v,
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None => {}
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}
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}
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// No linkage happens with rlibs, we just needed the metadata (which we
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// got long ago), so don't bother with anything.
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config::CrateTypeRlib => return Vec::new(),
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// Staticlibs must have all static dependencies. If any fail to be
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// found, we generate some nice pretty errors.
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config::CrateTypeStaticlib => {
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match attempt_static(sess) {
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Some(v) => return v,
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None => {}
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}
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for cnum in sess.cstore.crates() {
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let src = sess.cstore.used_crate_source(cnum);
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if src.rlib.is_some() { continue }
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sess.err(&format!("dependency `{}` not found in rlib format",
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sess.cstore.crate_name(cnum)));
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}
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return Vec::new();
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}
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// Generating a dylib without `-C prefer-dynamic` means that we're going
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// to try to eagerly statically link all dependencies. This is normally
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// done for end-product dylibs, not intermediate products.
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config::CrateTypeDylib if !sess.opts.cg.prefer_dynamic => {
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match attempt_static(sess) {
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Some(v) => return v,
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None => {}
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}
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}
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// Everything else falls through below
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config::CrateTypeExecutable | config::CrateTypeDylib => {},
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}
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let mut formats = FnvHashMap();
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// Sweep all crates for found dylibs. Add all dylibs, as well as their
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// dependencies, ensuring there are no conflicts. The only valid case for a
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// dependency to be relied upon twice is for both cases to rely on a dylib.
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for cnum in sess.cstore.crates() {
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let name = sess.cstore.crate_name(cnum);
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let src = sess.cstore.used_crate_source(cnum);
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if src.dylib.is_some() {
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info!("adding dylib: {}", name);
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add_library(sess, cnum, RequireDynamic, &mut formats);
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let deps = sess.cstore.dylib_dependency_formats(cnum);
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for &(depnum, style) in &deps {
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info!("adding {:?}: {}", style,
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sess.cstore.crate_name(depnum));
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add_library(sess, depnum, style, &mut formats);
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}
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}
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}
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// Collect what we've got so far in the return vector.
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let last_crate = sess.cstore.crates().len() as ast::CrateNum;
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let mut ret = (1..last_crate+1).map(|cnum| {
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match formats.get(&cnum) {
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Some(&RequireDynamic) => Linkage::Dynamic,
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Some(&RequireStatic) => Linkage::IncludedFromDylib,
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None => Linkage::NotLinked,
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}
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}).collect::<Vec<_>>();
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// Run through the dependency list again, and add any missing libraries as
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// static libraries.
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//
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// If the crate hasn't been included yet and it's not actually required
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// (e.g. it's an allocator) then we skip it here as well.
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for cnum in sess.cstore.crates() {
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let src = sess.cstore.used_crate_source(cnum);
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if src.dylib.is_none() &&
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!formats.contains_key(&cnum) &&
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sess.cstore.is_explicitly_linked(cnum) {
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assert!(src.rlib.is_some());
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info!("adding staticlib: {}", sess.cstore.crate_name(cnum));
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add_library(sess, cnum, RequireStatic, &mut formats);
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ret[cnum as usize - 1] = Linkage::Static;
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}
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}
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// We've gotten this far because we're emitting some form of a final
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// artifact which means that we're going to need an allocator of some form.
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// No allocator may have been required or linked so far, so activate one
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// here if one isn't set.
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activate_allocator(sess, &mut ret);
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// When dylib B links to dylib A, then when using B we must also link to A.
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// It could be the case, however, that the rlib for A is present (hence we
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// found metadata), but the dylib for A has since been removed.
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//
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// For situations like this, we perform one last pass over the dependencies,
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// making sure that everything is available in the requested format.
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for (cnum, kind) in ret.iter().enumerate() {
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let cnum = (cnum + 1) as ast::CrateNum;
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let src = sess.cstore.used_crate_source(cnum);
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match *kind {
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Linkage::NotLinked |
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Linkage::IncludedFromDylib => {}
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Linkage::Static if src.rlib.is_some() => continue,
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Linkage::Dynamic if src.dylib.is_some() => continue,
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kind => {
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let kind = match kind {
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Linkage::Static => "rlib",
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_ => "dylib",
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};
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let name = sess.cstore.crate_name(cnum);
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sess.err(&format!("crate `{}` required to be available in {}, \
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but it was not available in this form",
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name, kind));
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}
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}
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}
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return ret;
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}
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fn add_library(sess: &session::Session,
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cnum: ast::CrateNum,
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link: LinkagePreference,
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m: &mut FnvHashMap<ast::CrateNum, LinkagePreference>) {
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match m.get(&cnum) {
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Some(&link2) => {
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// If the linkages differ, then we'd have two copies of the library
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// if we continued linking. If the linkages are both static, then we
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// would also have two copies of the library (static from two
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// different locations).
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//
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// This error is probably a little obscure, but I imagine that it
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// can be refined over time.
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if link2 != link || link == RequireStatic {
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sess.struct_err(&format!("cannot satisfy dependencies so `{}` only \
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shows up once", sess.cstore.crate_name(cnum)))
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.help("having upstream crates all available in one format \
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will likely make this go away")
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.emit();
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}
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}
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None => { m.insert(cnum, link); }
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}
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}
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fn attempt_static(sess: &session::Session) -> Option<DependencyList> {
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let crates = sess.cstore.used_crates(RequireStatic);
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if !crates.iter().by_ref().all(|&(_, ref p)| p.is_some()) {
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return None
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}
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// All crates are available in an rlib format, so we're just going to link
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// everything in explicitly so long as it's actually required.
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let last_crate = sess.cstore.crates().len() as ast::CrateNum;
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let mut ret = (1..last_crate+1).map(|cnum| {
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if sess.cstore.is_explicitly_linked(cnum) {
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Linkage::Static
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} else {
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Linkage::NotLinked
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}
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}).collect::<Vec<_>>();
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// Our allocator may not have been activated as it's not flagged with
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// explicitly_linked, so flag it here if necessary.
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activate_allocator(sess, &mut ret);
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Some(ret)
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}
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// Given a list of how to link upstream dependencies so far, ensure that an
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// allocator is activated. This will not do anything if one was transitively
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// included already (e.g. via a dylib or explicitly so).
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//
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// If an allocator was not found then we're guaranteed the metadata::creader
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// module has injected an allocator dependency (not listed as a required
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// dependency) in the session's `injected_allocator` field. If this field is not
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// set then this compilation doesn't actually need an allocator and we can also
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// skip this step entirely.
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fn activate_allocator(sess: &session::Session, list: &mut DependencyList) {
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let mut allocator_found = false;
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for (i, slot) in list.iter().enumerate() {
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let cnum = (i + 1) as ast::CrateNum;
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if !sess.cstore.is_allocator(cnum) {
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continue
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}
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if let Linkage::NotLinked = *slot {
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continue
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}
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allocator_found = true;
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}
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if !allocator_found {
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if let Some(injected_allocator) = sess.injected_allocator.get() {
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let idx = injected_allocator as usize - 1;
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assert_eq!(list[idx], Linkage::NotLinked);
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list[idx] = Linkage::Static;
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}
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}
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}
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// After the linkage for a crate has been determined we need to verify that
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// there's only going to be one allocator in the output.
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fn verify_ok(sess: &session::Session, list: &[Linkage]) {
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if list.len() == 0 {
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return
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}
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let mut allocator = None;
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for (i, linkage) in list.iter().enumerate() {
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let cnum = (i + 1) as ast::CrateNum;
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if !sess.cstore.is_allocator(cnum) {
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continue
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}
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if let Linkage::NotLinked = *linkage {
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continue
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}
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if let Some(prev_alloc) = allocator {
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let prev_name = sess.cstore.crate_name(prev_alloc);
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let cur_name = sess.cstore.crate_name(cnum);
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sess.err(&format!("cannot link together two \
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allocators: {} and {}",
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prev_name, cur_name));
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}
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allocator = Some(cnum);
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}
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}
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