1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
//! 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::dependency_format::{Dependencies, DependencyList, Linkage};
use rustc_middle::ty::TyCtxt;
use rustc_session::config::CrateType;
use rustc_session::cstore::CrateDepKind;
use rustc_session::cstore::LinkagePreference::{self, RequireDynamic, RequireStatic};
use rustc_target::spec::PanicStrategy;

pub(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.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() {
            tracing::info!("adding dylib: {}", name);
            add_library(tcx, cnum, RequireDynamic, &mut formats);
            let deps = tcx.dylib_dependency_formats(cnum);
            for &(depnum, style) in deps.iter() {
                tracing::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) == CrateDepKind::Explicit
        {
            assert!(src.rlib.is_some() || src.rmeta.is_some());
            tracing::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 all_crates_available_as_rlib = tcx
        .crates(())
        .iter()
        .copied()
        .filter_map(|cnum| {
            if tcx.dep_kind(cnum).macros_only() {
                return None;
            }
            Some(tcx.used_crate_source(cnum).rlib.is_some())
        })
        .all(|is_rlib| is_rlib);
    if !all_crates_available_as_rlib {
        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 mut ret = tcx
        .crates(())
        .iter()
        .map(|&cnum| {
            if tcx.dep_kind(cnum) == CrateDepKind::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);
            if tcx.is_compiler_builtins(cnum) {
                continue;
            }

            let found_strategy = tcx.panic_strategy(cnum);
            if desired_strategy != found_strategy {
                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()
                ));
            }

            let found_drop_strategy = tcx.panic_in_drop_strategy(cnum);
            if tcx.sess.opts.debugging_opts.panic_in_drop != found_drop_strategy {
                sess.err(&format!(
                    "the crate `{}` is compiled with the \
                               panic-in-drop strategy `{}` which is \
                               incompatible with this crate's \
                               strategy of `{}`",
                    tcx.crate_name(cnum),
                    found_drop_strategy.desc(),
                    tcx.sess.opts.debugging_opts.panic_in_drop.desc()
                ));
            }
        }
    }
}