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Dylan-DPCDylan-DPC
authoredApr 17, 2022
Rollup merge of rust-lang#95604 - nbdd0121:used2, r=petrochenkov
Generate synthetic object file to ensure all exported and used symbols participate in the linking Fix rust-lang#50007 and rust-lang#47384 This is the synthetic object file approach that I described in rust-lang#95363 (comment), allowing all exported and used symbols to be linked while still allowing them to be GCed. Related rust-lang#93791, rust-lang#95363 r? `@petrochenkov` cc `@carbotaniuman`
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22 files changed

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‎compiler/rustc_codegen_llvm/src/back/lto.rs

+3-3
Original file line numberDiff line numberDiff line change
@@ -16,7 +16,7 @@ use rustc_errors::{FatalError, Handler};
1616
use rustc_hir::def_id::LOCAL_CRATE;
1717
use rustc_middle::bug;
1818
use rustc_middle::dep_graph::WorkProduct;
19-
use rustc_middle::middle::exported_symbols::SymbolExportLevel;
19+
use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
2020
use rustc_session::cgu_reuse_tracker::CguReuse;
2121
use rustc_session::config::{self, CrateType, Lto};
2222
use tracing::{debug, info};
@@ -55,8 +55,8 @@ fn prepare_lto(
5555
Lto::No => panic!("didn't request LTO but we're doing LTO"),
5656
};
5757

58-
let symbol_filter = &|&(ref name, level): &(String, SymbolExportLevel)| {
59-
if level.is_below_threshold(export_threshold) {
58+
let symbol_filter = &|&(ref name, info): &(String, SymbolExportInfo)| {
59+
if info.level.is_below_threshold(export_threshold) {
6060
Some(CString::new(name.as_str()).unwrap())
6161
} else {
6262
None

‎compiler/rustc_codegen_ssa/src/back/link.rs

+69
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@ use rustc_errors::{ErrorGuaranteed, Handler};
77
use rustc_fs_util::fix_windows_verbatim_for_gcc;
88
use rustc_hir::def_id::CrateNum;
99
use rustc_middle::middle::dependency_format::Linkage;
10+
use rustc_middle::middle::exported_symbols::SymbolExportKind;
1011
use rustc_session::config::{self, CFGuard, CrateType, DebugInfo, LdImpl, Strip};
1112
use rustc_session::config::{OutputFilenames, OutputType, PrintRequest, SplitDwarfKind};
1213
use rustc_session::cstore::DllImport;
@@ -1655,6 +1656,67 @@ fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor
16551656
}
16561657
}
16571658

1659+
/// Add a synthetic object file that contains reference to all symbols that we want to expose to
1660+
/// the linker.
1661+
///
1662+
/// Background: we implement rlibs as static library (archives). Linkers treat archives
1663+
/// differently from object files: all object files participate in linking, while archives will
1664+
/// only participate in linking if they can satisfy at least one undefined reference (version
1665+
/// scripts doesn't count). This causes `#[no_mangle]` or `#[used]` items to be ignored by the
1666+
/// linker, and since they never participate in the linking, using `KEEP` in the linker scripts
1667+
/// can't keep them either. This causes #47384.
1668+
///
1669+
/// To keep them around, we could use `--whole-archive` and equivalents to force rlib to
1670+
/// participate in linking like object files, but this proves to be expensive (#93791). Therefore
1671+
/// we instead just introduce an undefined reference to them. This could be done by `-u` command
1672+
/// line option to the linker or `EXTERN(...)` in linker scripts, however they does not only
1673+
/// introduce an undefined reference, but also make them the GC roots, preventing `--gc-sections`
1674+
/// from removing them, and this is especially problematic for embedded programming where every
1675+
/// byte counts.
1676+
///
1677+
/// This method creates a synthetic object file, which contains undefined references to all symbols
1678+
/// that are necessary for the linking. They are only present in symbol table but not actually
1679+
/// used in any sections, so the linker will therefore pick relevant rlibs for linking, but
1680+
/// unused `#[no_mangle]` or `#[used]` can still be discard by GC sections.
1681+
fn add_linked_symbol_object(
1682+
cmd: &mut dyn Linker,
1683+
sess: &Session,
1684+
tmpdir: &Path,
1685+
symbols: &[(String, SymbolExportKind)],
1686+
) {
1687+
if symbols.is_empty() {
1688+
return;
1689+
}
1690+
1691+
let Some(mut file) = super::metadata::create_object_file(sess) else {
1692+
return;
1693+
};
1694+
1695+
for (sym, kind) in symbols.iter() {
1696+
file.add_symbol(object::write::Symbol {
1697+
name: sym.clone().into(),
1698+
value: 0,
1699+
size: 0,
1700+
kind: match kind {
1701+
SymbolExportKind::Text => object::SymbolKind::Text,
1702+
SymbolExportKind::Data => object::SymbolKind::Data,
1703+
SymbolExportKind::Tls => object::SymbolKind::Tls,
1704+
},
1705+
scope: object::SymbolScope::Unknown,
1706+
weak: false,
1707+
section: object::write::SymbolSection::Undefined,
1708+
flags: object::SymbolFlags::None,
1709+
});
1710+
}
1711+
1712+
let path = tmpdir.join("symbols.o");
1713+
let result = std::fs::write(&path, file.write().unwrap());
1714+
if let Err(e) = result {
1715+
sess.fatal(&format!("failed to write {}: {}", path.display(), e));
1716+
}
1717+
cmd.add_object(&path);
1718+
}
1719+
16581720
/// Add object files containing code from the current crate.
16591721
fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
16601722
for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
@@ -1795,6 +1857,13 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
17951857
// Pre-link CRT objects.
17961858
add_pre_link_objects(cmd, sess, link_output_kind, crt_objects_fallback);
17971859

1860+
add_linked_symbol_object(
1861+
cmd,
1862+
sess,
1863+
tmpdir,
1864+
&codegen_results.crate_info.linked_symbols[&crate_type],
1865+
);
1866+
17981867
// Sanitizer libraries.
17991868
add_sanitizer_libraries(sess, crate_type, cmd);
18001869

‎compiler/rustc_codegen_ssa/src/back/linker.rs

+50-22
Original file line numberDiff line numberDiff line change
@@ -12,6 +12,7 @@ use std::{env, mem, str};
1212

1313
use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
1414
use rustc_middle::middle::dependency_format::Linkage;
15+
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
1516
use rustc_middle::ty::TyCtxt;
1617
use rustc_serialize::{json, Encoder};
1718
use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
@@ -1518,6 +1519,29 @@ impl<'a> L4Bender<'a> {
15181519
}
15191520
}
15201521

1522+
fn for_each_exported_symbols_include_dep<'tcx>(
1523+
tcx: TyCtxt<'tcx>,
1524+
crate_type: CrateType,
1525+
mut callback: impl FnMut(ExportedSymbol<'tcx>, SymbolExportInfo, CrateNum),
1526+
) {
1527+
for &(symbol, info) in tcx.exported_symbols(LOCAL_CRATE).iter() {
1528+
callback(symbol, info, LOCAL_CRATE);
1529+
}
1530+
1531+
let formats = tcx.dependency_formats(());
1532+
let deps = formats.iter().find_map(|(t, list)| (*t == crate_type).then_some(list)).unwrap();
1533+
1534+
for (index, dep_format) in deps.iter().enumerate() {
1535+
let cnum = CrateNum::new(index + 1);
1536+
// For each dependency that we are linking to statically ...
1537+
if *dep_format == Linkage::Static {
1538+
for &(symbol, info) in tcx.exported_symbols(cnum).iter() {
1539+
callback(symbol, info, cnum);
1540+
}
1541+
}
1542+
}
1543+
}
1544+
15211545
pub(crate) fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
15221546
if let Some(ref exports) = tcx.sess.target.override_export_symbols {
15231547
return exports.iter().map(ToString::to_string).collect();
@@ -1526,34 +1550,38 @@ pub(crate) fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<St
15261550
let mut symbols = Vec::new();
15271551

15281552
let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
1529-
for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
1530-
if level.is_below_threshold(export_threshold) {
1531-
symbols.push(symbol_export::symbol_name_for_instance_in_crate(
1532-
tcx,
1533-
symbol,
1534-
LOCAL_CRATE,
1535-
));
1553+
for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
1554+
if info.level.is_below_threshold(export_threshold) {
1555+
symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
15361556
}
1537-
}
1557+
});
15381558

1539-
let formats = tcx.dependency_formats(());
1540-
let deps = formats.iter().find_map(|(t, list)| (*t == crate_type).then_some(list)).unwrap();
1541-
1542-
for (index, dep_format) in deps.iter().enumerate() {
1543-
let cnum = CrateNum::new(index + 1);
1544-
// For each dependency that we are linking to statically ...
1545-
if *dep_format == Linkage::Static {
1546-
// ... we add its symbol list to our export list.
1547-
for &(symbol, level) in tcx.exported_symbols(cnum).iter() {
1548-
if !level.is_below_threshold(export_threshold) {
1549-
continue;
1550-
}
1559+
symbols
1560+
}
15511561

1552-
symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
1553-
}
1562+
pub(crate) fn linked_symbols(
1563+
tcx: TyCtxt<'_>,
1564+
crate_type: CrateType,
1565+
) -> Vec<(String, SymbolExportKind)> {
1566+
match crate_type {
1567+
CrateType::Executable | CrateType::Cdylib => (),
1568+
CrateType::Staticlib | CrateType::ProcMacro | CrateType::Rlib | CrateType::Dylib => {
1569+
return Vec::new();
15541570
}
15551571
}
15561572

1573+
let mut symbols = Vec::new();
1574+
1575+
let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
1576+
for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
1577+
if info.level.is_below_threshold(export_threshold) || info.used {
1578+
symbols.push((
1579+
symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum),
1580+
info.kind,
1581+
));
1582+
}
1583+
});
1584+
15571585
symbols
15581586
}
15591587

‎compiler/rustc_codegen_ssa/src/back/metadata.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -94,7 +94,7 @@ fn search_for_metadata<'a>(
9494
.map_err(|e| format!("failed to read {} section in '{}': {}", section, path.display(), e))
9595
}
9696

97-
fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
97+
pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
9898
let endianness = match sess.target.options.endian {
9999
Endian::Little => Endianness::Little,
100100
Endian::Big => Endianness::Big,

‎compiler/rustc_codegen_ssa/src/back/symbol_export.rs

+85-15
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@ use rustc_hir::Node;
99
use rustc_index::vec::IndexVec;
1010
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
1111
use rustc_middle::middle::exported_symbols::{
12-
metadata_symbol_name, ExportedSymbol, SymbolExportLevel,
12+
metadata_symbol_name, ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
1313
};
1414
use rustc_middle::ty::query::{ExternProviders, Providers};
1515
use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
@@ -42,7 +42,7 @@ pub fn crates_export_threshold(crate_types: &[CrateType]) -> SymbolExportLevel {
4242
}
4343
}
4444

45-
fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<SymbolExportLevel> {
45+
fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<SymbolExportInfo> {
4646
assert_eq!(cnum, LOCAL_CRATE);
4747

4848
if !tcx.sess.opts.output_types.should_codegen() {
@@ -124,17 +124,38 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<
124124
} else {
125125
symbol_export_level(tcx, def_id.to_def_id())
126126
};
127+
let codegen_attrs = tcx.codegen_fn_attrs(def_id.to_def_id());
127128
debug!(
128129
"EXPORTED SYMBOL (local): {} ({:?})",
129130
tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())),
130131
export_level
131132
);
132-
(def_id.to_def_id(), export_level)
133+
(def_id.to_def_id(), SymbolExportInfo {
134+
level: export_level,
135+
kind: if tcx.is_static(def_id.to_def_id()) {
136+
if codegen_attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
137+
SymbolExportKind::Tls
138+
} else {
139+
SymbolExportKind::Data
140+
}
141+
} else {
142+
SymbolExportKind::Text
143+
},
144+
used: codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
145+
|| codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER),
146+
})
133147
})
134148
.collect();
135149

136150
if let Some(id) = tcx.proc_macro_decls_static(()) {
137-
reachable_non_generics.insert(id.to_def_id(), SymbolExportLevel::C);
151+
reachable_non_generics.insert(
152+
id.to_def_id(),
153+
SymbolExportInfo {
154+
level: SymbolExportLevel::C,
155+
kind: SymbolExportKind::Data,
156+
used: false,
157+
},
158+
);
138159
}
139160

140161
reachable_non_generics
@@ -143,8 +164,8 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<
143164
fn is_reachable_non_generic_provider_local(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
144165
let export_threshold = threshold(tcx);
145166

146-
if let Some(&level) = tcx.reachable_non_generics(def_id.krate).get(&def_id) {
147-
level.is_below_threshold(export_threshold)
167+
if let Some(&info) = tcx.reachable_non_generics(def_id.krate).get(&def_id) {
168+
info.level.is_below_threshold(export_threshold)
148169
} else {
149170
false
150171
}
@@ -157,7 +178,7 @@ fn is_reachable_non_generic_provider_extern(tcx: TyCtxt<'_>, def_id: DefId) -> b
157178
fn exported_symbols_provider_local<'tcx>(
158179
tcx: TyCtxt<'tcx>,
159180
cnum: CrateNum,
160-
) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportLevel)] {
181+
) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
161182
assert_eq!(cnum, LOCAL_CRATE);
162183

163184
if !tcx.sess.opts.output_types.should_codegen() {
@@ -167,21 +188,35 @@ fn exported_symbols_provider_local<'tcx>(
167188
let mut symbols: Vec<_> = tcx
168189
.reachable_non_generics(LOCAL_CRATE)
169190
.iter()
170-
.map(|(&def_id, &level)| (ExportedSymbol::NonGeneric(def_id), level))
191+
.map(|(&def_id, &info)| (ExportedSymbol::NonGeneric(def_id), info))
171192
.collect();
172193

173194
if tcx.entry_fn(()).is_some() {
174195
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, "main"));
175196

176-
symbols.push((exported_symbol, SymbolExportLevel::C));
197+
symbols.push((
198+
exported_symbol,
199+
SymbolExportInfo {
200+
level: SymbolExportLevel::C,
201+
kind: SymbolExportKind::Text,
202+
used: false,
203+
},
204+
));
177205
}
178206

179207
if tcx.allocator_kind(()).is_some() {
180208
for method in ALLOCATOR_METHODS {
181209
let symbol_name = format!("__rust_{}", method.name);
182210
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
183211

184-
symbols.push((exported_symbol, SymbolExportLevel::Rust));
212+
symbols.push((
213+
exported_symbol,
214+
SymbolExportInfo {
215+
level: SymbolExportLevel::Rust,
216+
kind: SymbolExportKind::Text,
217+
used: false,
218+
},
219+
));
185220
}
186221
}
187222

@@ -194,7 +229,14 @@ fn exported_symbols_provider_local<'tcx>(
194229

195230
symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
196231
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
197-
(exported_symbol, SymbolExportLevel::C)
232+
(
233+
exported_symbol,
234+
SymbolExportInfo {
235+
level: SymbolExportLevel::C,
236+
kind: SymbolExportKind::Data,
237+
used: false,
238+
},
239+
)
198240
}));
199241
}
200242

@@ -204,15 +246,29 @@ fn exported_symbols_provider_local<'tcx>(
204246

205247
symbols.extend(MSAN_WEAK_SYMBOLS.iter().map(|sym| {
206248
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
207-
(exported_symbol, SymbolExportLevel::C)
249+
(
250+
exported_symbol,
251+
SymbolExportInfo {
252+
level: SymbolExportLevel::C,
253+
kind: SymbolExportKind::Data,
254+
used: false,
255+
},
256+
)
208257
}));
209258
}
210259

211260
if tcx.sess.crate_types().contains(&CrateType::Dylib) {
212261
let symbol_name = metadata_symbol_name(tcx);
213262
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
214263

215-
symbols.push((exported_symbol, SymbolExportLevel::Rust));
264+
symbols.push((
265+
exported_symbol,
266+
SymbolExportInfo {
267+
level: SymbolExportLevel::Rust,
268+
kind: SymbolExportKind::Data,
269+
used: false,
270+
},
271+
));
216272
}
217273

218274
if tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics() {
@@ -245,7 +301,14 @@ fn exported_symbols_provider_local<'tcx>(
245301
MonoItem::Fn(Instance { def: InstanceDef::Item(def), substs }) => {
246302
if substs.non_erasable_generics().next().is_some() {
247303
let symbol = ExportedSymbol::Generic(def.did, substs);
248-
symbols.push((symbol, SymbolExportLevel::Rust));
304+
symbols.push((
305+
symbol,
306+
SymbolExportInfo {
307+
level: SymbolExportLevel::Rust,
308+
kind: SymbolExportKind::Text,
309+
used: false,
310+
},
311+
));
249312
}
250313
}
251314
MonoItem::Fn(Instance { def: InstanceDef::DropGlue(_, Some(ty)), substs }) => {
@@ -254,7 +317,14 @@ fn exported_symbols_provider_local<'tcx>(
254317
substs.non_erasable_generics().next(),
255318
Some(GenericArgKind::Type(ty))
256319
);
257-
symbols.push((ExportedSymbol::DropGlue(ty), SymbolExportLevel::Rust));
320+
symbols.push((
321+
ExportedSymbol::DropGlue(ty),
322+
SymbolExportInfo {
323+
level: SymbolExportLevel::Rust,
324+
kind: SymbolExportKind::Text,
325+
used: false,
326+
},
327+
));
258328
}
259329
_ => {
260330
// Any other symbols don't qualify for sharing

‎compiler/rustc_codegen_ssa/src/back/write.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@ use rustc_incremental::{
2323
};
2424
use rustc_metadata::EncodedMetadata;
2525
use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
26-
use rustc_middle::middle::exported_symbols::SymbolExportLevel;
26+
use rustc_middle::middle::exported_symbols::SymbolExportInfo;
2727
use rustc_middle::ty::TyCtxt;
2828
use rustc_session::cgu_reuse_tracker::CguReuseTracker;
2929
use rustc_session::config::{self, CrateType, Lto, OutputFilenames, OutputType};
@@ -304,7 +304,7 @@ pub type TargetMachineFactoryFn<B> = Arc<
304304
+ Sync,
305305
>;
306306

307-
pub type ExportedSymbols = FxHashMap<CrateNum, Arc<Vec<(String, SymbolExportLevel)>>>;
307+
pub type ExportedSymbols = FxHashMap<CrateNum, Arc<Vec<(String, SymbolExportInfo)>>>;
308308

309309
/// Additional resources used by optimize_and_codegen (not module specific)
310310
#[derive(Clone)]

‎compiler/rustc_codegen_ssa/src/base.rs

+7
Original file line numberDiff line numberDiff line change
@@ -801,6 +801,12 @@ impl CrateInfo {
801801
.iter()
802802
.map(|&c| (c, crate::back::linker::exported_symbols(tcx, c)))
803803
.collect();
804+
let linked_symbols = tcx
805+
.sess
806+
.crate_types()
807+
.iter()
808+
.map(|&c| (c, crate::back::linker::linked_symbols(tcx, c)))
809+
.collect();
804810
let local_crate_name = tcx.crate_name(LOCAL_CRATE);
805811
let crate_attrs = tcx.hir().attrs(rustc_hir::CRATE_HIR_ID);
806812
let subsystem = tcx.sess.first_attr_value_str_by_name(crate_attrs, sym::windows_subsystem);
@@ -834,6 +840,7 @@ impl CrateInfo {
834840
let mut info = CrateInfo {
835841
target_cpu,
836842
exported_symbols,
843+
linked_symbols,
837844
local_crate_name,
838845
compiler_builtins: None,
839846
profiler_runtime: None,

‎compiler/rustc_codegen_ssa/src/lib.rs

+2
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,7 @@ use rustc_hir::def_id::CrateNum;
2828
use rustc_hir::LangItem;
2929
use rustc_middle::dep_graph::WorkProduct;
3030
use rustc_middle::middle::dependency_format::Dependencies;
31+
use rustc_middle::middle::exported_symbols::SymbolExportKind;
3132
use rustc_middle::ty::query::{ExternProviders, Providers};
3233
use rustc_serialize::{opaque, Decodable, Decoder, Encoder};
3334
use rustc_session::config::{CrateType, OutputFilenames, OutputType, RUST_CGU_EXT};
@@ -141,6 +142,7 @@ impl From<&cstore::NativeLib> for NativeLib {
141142
pub struct CrateInfo {
142143
pub target_cpu: String,
143144
pub exported_symbols: FxHashMap<CrateType, Vec<String>>,
145+
pub linked_symbols: FxHashMap<CrateType, Vec<(String, SymbolExportKind)>>,
144146
pub local_crate_name: Symbol,
145147
pub compiler_builtins: Option<CrateNum>,
146148
pub profiler_runtime: Option<CrateNum>,

‎compiler/rustc_metadata/src/rmeta/decoder.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@ use rustc_hir::lang_items;
2222
use rustc_index::vec::{Idx, IndexVec};
2323
use rustc_middle::arena::ArenaAllocatable;
2424
use rustc_middle::metadata::ModChild;
25-
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
25+
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
2626
use rustc_middle::middle::stability::DeprecationEntry;
2727
use rustc_middle::mir::interpret::{AllocDecodingSession, AllocDecodingState};
2828
use rustc_middle::thir;
@@ -1428,7 +1428,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
14281428
fn exported_symbols(
14291429
self,
14301430
tcx: TyCtxt<'tcx>,
1431-
) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportLevel)] {
1431+
) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
14321432
tcx.arena.alloc_from_iter(self.root.exported_symbols.decode((self, tcx)))
14331433
}
14341434

‎compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -190,9 +190,9 @@ provide! { <'tcx> tcx, def_id, other, cdata,
190190
let reachable_non_generics = tcx
191191
.exported_symbols(cdata.cnum)
192192
.iter()
193-
.filter_map(|&(exported_symbol, export_level)| {
193+
.filter_map(|&(exported_symbol, export_info)| {
194194
if let ExportedSymbol::NonGeneric(def_id) = exported_symbol {
195-
Some((def_id, export_level))
195+
Some((def_id, export_info))
196196
} else {
197197
None
198198
}

‎compiler/rustc_metadata/src/rmeta/encoder.rs

+3-3
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@ use rustc_index::vec::Idx;
2222
use rustc_middle::hir::nested_filter;
2323
use rustc_middle::middle::dependency_format::Linkage;
2424
use rustc_middle::middle::exported_symbols::{
25-
metadata_symbol_name, ExportedSymbol, SymbolExportLevel,
25+
metadata_symbol_name, ExportedSymbol, SymbolExportInfo,
2626
};
2727
use rustc_middle::mir::interpret;
2828
use rustc_middle::thir;
@@ -1865,8 +1865,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
18651865
// definition (as that's not defined in this crate).
18661866
fn encode_exported_symbols(
18671867
&mut self,
1868-
exported_symbols: &[(ExportedSymbol<'tcx>, SymbolExportLevel)],
1869-
) -> Lazy<[(ExportedSymbol<'tcx>, SymbolExportLevel)]> {
1868+
exported_symbols: &[(ExportedSymbol<'tcx>, SymbolExportInfo)],
1869+
) -> Lazy<[(ExportedSymbol<'tcx>, SymbolExportInfo)]> {
18701870
empty_proc_macro!(self);
18711871
// The metadata symbol name is special. It should not show up in
18721872
// downstream crates.

‎compiler/rustc_metadata/src/rmeta/mod.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@ use rustc_hir::definitions::DefKey;
1414
use rustc_hir::lang_items;
1515
use rustc_index::{bit_set::FiniteBitSet, vec::IndexVec};
1616
use rustc_middle::metadata::ModChild;
17-
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
17+
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
1818
use rustc_middle::mir;
1919
use rustc_middle::thir;
2020
use rustc_middle::ty::fast_reject::SimplifiedType;
@@ -219,7 +219,7 @@ crate struct CrateRoot<'tcx> {
219219

220220
tables: LazyTables<'tcx>,
221221

222-
exported_symbols: Lazy!([(ExportedSymbol<'tcx>, SymbolExportLevel)]),
222+
exported_symbols: Lazy!([(ExportedSymbol<'tcx>, SymbolExportInfo)]),
223223

224224
syntax_contexts: SyntaxContextTable,
225225
expn_data: ExpnDataTable,

‎compiler/rustc_middle/src/middle/exported_symbols.rs

+17
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,23 @@ impl SymbolExportLevel {
2121
}
2222
}
2323

24+
/// Kind of exported symbols.
25+
#[derive(Eq, PartialEq, Debug, Copy, Clone, Encodable, Decodable, HashStable)]
26+
pub enum SymbolExportKind {
27+
Text,
28+
Data,
29+
Tls,
30+
}
31+
32+
/// The `SymbolExportInfo` of a symbols specifies symbol-related information
33+
/// that is relevant to code generation and linking.
34+
#[derive(Eq, PartialEq, Debug, Copy, Clone, TyEncodable, TyDecodable, HashStable)]
35+
pub struct SymbolExportInfo {
36+
pub level: SymbolExportLevel,
37+
pub kind: SymbolExportKind,
38+
pub used: bool,
39+
}
40+
2441
#[derive(Eq, PartialEq, Debug, Copy, Clone, TyEncodable, TyDecodable, HashStable)]
2542
pub enum ExportedSymbol<'tcx> {
2643
NonGeneric(DefId),

‎compiler/rustc_middle/src/query/mod.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -1359,7 +1359,7 @@ rustc_queries! {
13591359
// Does not include external symbols that don't have a corresponding DefId,
13601360
// like the compiler-generated `main` function and so on.
13611361
query reachable_non_generics(_: CrateNum)
1362-
-> DefIdMap<SymbolExportLevel> {
1362+
-> DefIdMap<SymbolExportInfo> {
13631363
storage(ArenaCacheSelector<'tcx>)
13641364
desc { "looking up the exported symbols of a crate" }
13651365
separate_provide_extern
@@ -1675,7 +1675,7 @@ rustc_queries! {
16751675
/// correspond to a publicly visible symbol in `cnum` machine code.
16761676
/// - The `exported_symbols` sets of different crates do not intersect.
16771677
query exported_symbols(_: CrateNum)
1678-
-> &'tcx [(ExportedSymbol<'tcx>, SymbolExportLevel)] {
1678+
-> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
16791679
desc { "exported_symbols" }
16801680
separate_provide_extern
16811681
}

‎compiler/rustc_middle/src/ty/query.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@ use crate::infer::canonical::{self, Canonical};
33
use crate::lint::LintLevelMap;
44
use crate::metadata::ModChild;
55
use crate::middle::codegen_fn_attrs::CodegenFnAttrs;
6-
use crate::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
6+
use crate::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
77
use crate::middle::lib_features::LibFeatures;
88
use crate::middle::privacy::AccessLevels;
99
use crate::middle::region;

‎compiler/rustc_monomorphize/src/partitioning/default.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -5,7 +5,7 @@ use rustc_hir::def::DefKind;
55
use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
66
use rustc_hir::definitions::DefPathDataName;
77
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
8-
use rustc_middle::middle::exported_symbols::SymbolExportLevel;
8+
use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
99
use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, Linkage, Visibility};
1010
use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
1111
use rustc_middle::ty::print::characteristic_def_id_of_type;
@@ -554,7 +554,7 @@ fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibilit
554554
// C-export level items remain at `Default`, all other internal
555555
// items become `Hidden`.
556556
match tcx.reachable_non_generics(id.krate).get(&id) {
557-
Some(SymbolExportLevel::C) => Visibility::Default,
557+
Some(SymbolExportInfo { level: SymbolExportLevel::C, .. }) => Visibility::Default,
558558
_ => Visibility::Hidden,
559559
}
560560
}

‎compiler/rustc_passes/src/reachable.rs

+5
Original file line numberDiff line numberDiff line change
@@ -333,6 +333,11 @@ impl CollectPrivateImplItemsVisitor<'_, '_> {
333333
let codegen_attrs = self.tcx.codegen_fn_attrs(def_id);
334334
if codegen_attrs.contains_extern_indicator()
335335
|| codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
336+
// FIXME(nbdd0121): `#[used]` are marked as reachable here so it's picked up by
337+
// `linked_symbols` in cg_ssa. They won't be exported in binary or cdylib due to their
338+
// `SymbolExportLevel::Rust` export level but may end up being exported in dylibs.
339+
|| codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
340+
|| codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
336341
{
337342
self.worklist.push(def_id);
338343
}

‎src/test/run-make-fulldeps/reproducible-build/linker.rs

+6
Original file line numberDiff line numberDiff line change
@@ -25,6 +25,12 @@ fn main() {
2525
let mut contents = Vec::new();
2626
File::open(path).unwrap().read_to_end(&mut contents).unwrap();
2727

28+
// This file is produced during linking in a temporary directory.
29+
let arg = if arg.ends_with("/symbols.o") {
30+
"symbols.o"
31+
} else {
32+
&*arg
33+
};
2834
out.push_str(&format!("{}: {}\n", arg, hash(&contents)));
2935
}
3036

‎src/test/run-make/issue-47384/Makefile

+12
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
1+
-include ../../run-make-fulldeps/tools.mk
2+
3+
# only-linux
4+
# ignore-cross-compile
5+
6+
all: main.rs
7+
$(RUSTC) --crate-type lib lib.rs
8+
$(RUSTC) --crate-type cdylib -Clink-args="-Tlinker.ld" main.rs
9+
# Ensure `#[used]` and `KEEP`-ed section is there
10+
objdump -s -j".static" $(TMPDIR)/libmain.so
11+
# Ensure `#[no_mangle]` symbol is there
12+
nm $(TMPDIR)/libmain.so | $(CGREP) bar

‎src/test/run-make/issue-47384/lib.rs

+12
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
1+
mod foo {
2+
#[link_section = ".rodata.STATIC"]
3+
#[used]
4+
static STATIC: [u32; 10] = [1; 10];
5+
}
6+
7+
mod bar {
8+
#[no_mangle]
9+
extern "C" fn bar() -> i32 {
10+
0
11+
}
12+
}

‎src/test/run-make/issue-47384/linker.ld

+7
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,7 @@
1+
SECTIONS
2+
{
3+
.static : ALIGN(4)
4+
{
5+
KEEP(*(.rodata.STATIC));
6+
}
7+
}

‎src/test/run-make/issue-47384/main.rs

+1
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
extern crate lib;

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