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Ensure we emit an allocator shim when only some crate types need one #145962

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Merged
bors merged 4 commits into rust-lang:master from bjorn3:linkage_fixes
Sep 4, 2025
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17 changes: 13 additions & 4 deletions compiler/rustc_codegen_ssa/src/back/link.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ use super::linker::{self, Linker};
use super::metadata::{MetadataPosition, create_wrapper_file};
use super::rpath::{self, RPathConfig};
use super::{apple, versioned_llvm_target};
use crate::base::needs_allocator_shim_for_linking;
use crate::{
CodegenResults, CompiledModule, CrateInfo, NativeLib, errors, looks_like_rust_object_file,
};
Expand Down Expand Up @@ -2080,9 +2081,17 @@ fn add_local_crate_regular_objects(cmd: &mut dyn Linker, codegen_results: &Codeg
}

/// Add object files for allocator code linked once for the whole crate tree.
fn add_local_crate_allocator_objects(cmd: &mut dyn Linker, codegen_results: &CodegenResults) {
if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref()) {
cmd.add_object(obj);
fn add_local_crate_allocator_objects(
cmd: &mut dyn Linker,
codegen_results: &CodegenResults,
crate_type: CrateType,
) {
if needs_allocator_shim_for_linking(&codegen_results.crate_info.dependency_formats, crate_type)
{
if let Some(obj) = codegen_results.allocator_module.as_ref().and_then(|m| m.object.as_ref())
{
cmd.add_object(obj);
}
}
}

Expand Down Expand Up @@ -2281,7 +2290,7 @@ fn linker_with_args(
codegen_results,
metadata,
);
add_local_crate_allocator_objects(cmd, codegen_results);
add_local_crate_allocator_objects(cmd, codegen_results, crate_type);

// Avoid linking to dynamic libraries unless they satisfy some undefined symbols
// at the point at which they are specified on the command line.
Expand Down
17 changes: 14 additions & 3 deletions compiler/rustc_codegen_ssa/src/back/linker.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,9 @@ use rustc_metadata::{
};
use rustc_middle::bug;
use rustc_middle::middle::dependency_format::Linkage;
use rustc_middle::middle::exported_symbols;
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo, SymbolExportKind};
use rustc_middle::middle::exported_symbols::{
self, ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
};
use rustc_middle::ty::TyCtxt;
use rustc_session::Session;
use rustc_session::config::{self, CrateType, DebugInfo, LinkerPluginLto, Lto, OptLevel, Strip};
Expand All @@ -22,6 +23,8 @@ use tracing::{debug, warn};

use super::command::Command;
use super::symbol_export;
use crate::back::symbol_export::allocator_shim_symbols;
use crate::base::needs_allocator_shim_for_linking;
use crate::errors;

#[cfg(test)]
Expand Down Expand Up @@ -1827,7 +1830,7 @@ fn exported_symbols_for_non_proc_macro(
let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
// Do not export mangled symbols from cdylibs and don't attempt to export compiler-builtins
// from any cdylib. The latter doesn't work anyway as we use hidden visibility for
// from any dylib. The latter doesn't work anyway as we use hidden visibility for
// compiler-builtins. Most linkers silently ignore it, but ld64 gives a warning.
if info.level.is_below_threshold(export_threshold) && !tcx.is_compiler_builtins(cnum) {
symbols.push((
Expand All @@ -1838,6 +1841,14 @@ fn exported_symbols_for_non_proc_macro(
}
});

// Mark allocator shim symbols as exported only if they were generated.
if export_threshold == SymbolExportLevel::Rust
&& needs_allocator_shim_for_linking(tcx.dependency_formats(()), crate_type)
&& tcx.allocator_kind(()).is_some()
{
symbols.extend(allocator_shim_symbols(tcx));
}

symbols
}

Expand Down
8 changes: 7 additions & 1 deletion compiler/rustc_codegen_ssa/src/back/lto.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,9 @@ use rustc_middle::ty::TyCtxt;
use rustc_session::config::{CrateType, Lto};
use tracing::info;

use crate::back::symbol_export::{self, symbol_name_for_instance_in_crate};
use crate::back::symbol_export::{self, allocator_shim_symbols, symbol_name_for_instance_in_crate};
use crate::back::write::CodegenContext;
use crate::base::allocator_kind_for_codegen;
use crate::errors::{DynamicLinkingWithLTO, LtoDisallowed, LtoDylib, LtoProcMacro};
use crate::traits::*;

Expand Down Expand Up @@ -115,6 +116,11 @@ pub(super) fn exported_symbols_for_lto(
}
}

// Mark allocator shim symbols as exported only if they were generated.
if export_threshold == SymbolExportLevel::Rust && allocator_kind_for_codegen(tcx).is_some() {
symbols_below_threshold.extend(allocator_shim_symbols(tcx).map(|(name, _kind)| name));
}

symbols_below_threshold
}

Expand Down
52 changes: 26 additions & 26 deletions compiler/rustc_codegen_ssa/src/back/symbol_export.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ use rustc_symbol_mangling::mangle_internal_symbol;
use rustc_target::spec::TlsModel;
use tracing::debug;

use crate::base::allocator_kind_for_codegen;
use crate::back::symbol_export;

fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
crates_export_threshold(tcx.crate_types())
Expand Down Expand Up @@ -217,31 +217,6 @@ fn exported_non_generic_symbols_provider_local<'tcx>(
));
}

// Mark allocator shim symbols as exported only if they were generated.
if allocator_kind_for_codegen(tcx).is_some() {
for symbol_name in ALLOCATOR_METHODS
.iter()
.map(|method| mangle_internal_symbol(tcx, global_fn_name(method.name).as_str()))
.chain([
mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
])
{
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));

symbols.push((
exported_symbol,
SymbolExportInfo {
level: SymbolExportLevel::Rust,
kind: SymbolExportKind::Text,
used: false,
rustc_std_internal_symbol: true,
},
));
}
}

// Sort so we get a stable incr. comp. hash.
symbols.sort_by_cached_key(|s| s.0.symbol_name_for_local_instance(tcx));

Expand Down Expand Up @@ -516,6 +491,31 @@ pub(crate) fn provide(providers: &mut Providers) {
upstream_monomorphizations_for_provider;
}

pub(crate) fn allocator_shim_symbols(
tcx: TyCtxt<'_>,
) -> impl Iterator<Item = (String, SymbolExportKind)> {
ALLOCATOR_METHODS
.iter()
.map(move |method| mangle_internal_symbol(tcx, global_fn_name(method.name).as_str()))
.chain([
mangle_internal_symbol(tcx, "__rust_alloc_error_handler"),
mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
])
.map(move |symbol_name| {
let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));

(
symbol_export::exporting_symbol_name_for_instance_in_crate(
tcx,
exported_symbol,
LOCAL_CRATE,
),
SymbolExportKind::Text,
)
})
}

fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel {
// We export anything that's not mangled at the "C" layer as it probably has
// to do with ABI concerns. We do not, however, apply such treatment to
Expand Down
27 changes: 22 additions & 5 deletions compiler/rustc_codegen_ssa/src/base.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ use rustc_hir::lang_items::LangItem;
use rustc_hir::{ItemId, Target};
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
use rustc_middle::middle::debugger_visualizer::{DebuggerVisualizerFile, DebuggerVisualizerType};
use rustc_middle::middle::dependency_format::Dependencies;
use rustc_middle::middle::exported_symbols::{self, SymbolExportKind};
use rustc_middle::middle::lang_items;
use rustc_middle::mir::BinOp;
Expand Down Expand Up @@ -630,14 +631,30 @@ pub fn allocator_kind_for_codegen(tcx: TyCtxt<'_>) -> Option<AllocatorKind> {
// If the crate doesn't have an `allocator_kind` set then there's definitely
// no shim to generate. Otherwise we also check our dependency graph for all
// our output crate types. If anything there looks like its a `Dynamic`
// linkage, then it's already got an allocator shim and we'll be using that
// one instead. If nothing exists then it's our job to generate the
// allocator!
let any_dynamic_crate = tcx.dependency_formats(()).iter().any(|(_, list)| {
// linkage for all crate types we may link as, then it's already got an
// allocator shim and we'll be using that one instead. If nothing exists
// then it's our job to generate the allocator! If crate types disagree
// about whether an allocator shim is necessary or not, we generate one
// and let needs_allocator_shim_for_linking decide at link time whether or
// not to use it for any particular linker invocation.
let all_crate_types_any_dynamic_crate = tcx.dependency_formats(()).iter().all(|(_, list)| {
use rustc_middle::middle::dependency_format::Linkage;
list.iter().any(|&linkage| linkage == Linkage::Dynamic)
});
if any_dynamic_crate { None } else { tcx.allocator_kind(()) }
if all_crate_types_any_dynamic_crate { None } else { tcx.allocator_kind(()) }
}

/// Decide if this particular crate type needs an allocator shim linked in.
/// This may return true even when allocator_kind_for_codegen returns false. In
/// this case no allocator shim shall be linked.
pub(crate) fn needs_allocator_shim_for_linking(
dependency_formats: &Dependencies,
crate_type: CrateType,
) -> bool {
use rustc_middle::middle::dependency_format::Linkage;
let any_dynamic_crate =
dependency_formats[&crate_type].iter().any(|&linkage| linkage == Linkage::Dynamic);
!any_dynamic_crate
}

pub fn codegen_crate<B: ExtraBackendMethods>(
Expand Down
16 changes: 16 additions & 0 deletions tests/ui/linking/mixed-allocator-shim.rs
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
//@ build-pass
//@ compile-flags: --crate-type staticlib,dylib -Zstaticlib-prefer-dynamic
//@ no-prefer-dynamic
//@ needs-crate-type: dylib

// Test that compiling for multiple crate types in a single compilation with
// mismatching allocator shim requirements doesn't result in the allocator shim
// missing entirely.
// In this particular test the dylib crate type will statically link libstd and
// thus need an allocator shim, while the staticlib crate type will dynamically
// link libstd and thus not need an allocator shim.
// The -Zstaticlib-prefer-dynamic flag could be avoided by doing it the other
// way around, but testing that the staticlib correctly has the allocator shim
// in that case would require a run-make test instead.

pub fn foo() {}
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