Rename symbols rather than add symbol aliases for EIIs when possible by bjorn3 · Pull Request #159843 · rust-lang/rust

bjorn3 · 2026-07-24T14:24:13Z

The symbol name of the EII impl will now get changed to match the EII decl whenever there is no default impl. This already works across all backends and targets unlike the weak symbol aliases that we currently use. When there is a default impl, we will still use weak symbol aliases.

Based on #159326 and #159374

This allows implementing EIIs that don't have a default impl without the involvement of symbol aliases by simply changing the mangled symbol name of the implementation, which would make them trivially compatible with all backends and targets. This change will be left to a followup PR.

This reduces the amount of special casing #[no_mangle] needs in the rest of the compiler.

The symbol name of the EII impl will now get changed to match the EII decl whenever there is no default impl. This already works across all backends and targets unlike the weak symbol aliases that we currently use. When there is a default impl, we will still use weak symbol aliases.

rust-log-analyzer · 2026-07-24T14:59:25Z

The job aarch64-gnu-llvm-21-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

   9:     0xff1ef2fc8330 - std[faaa1722a6c2e07a]::panicking::default_hook::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:292:27
  10:     0xff1ef2fe7db4 - std[faaa1722a6c2e07a]::panicking::default_hook
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:319:9
  11:     0xff1eef6d83f4 - std[faaa1722a6c2e07a]::panicking::update_hook::<alloc[7220a3968fb26a7c]::boxed::Box<rustc_driver_impl[7b725a2f7bf77b9a]::install_ice_hook::{closure#1}>>::{closure#0}
  12:     0xff1ef2fe8130 - <alloc[7220a3968fb26a7c]::boxed::Box<dyn for<'a, 'b> core[a3bed6fa7f8910de]::ops::function::Fn<(&'a std[faaa1722a6c2e07a]::panic::PanicHookInfo<'b>,), Output = ()> + core[a3bed6fa7f8910de]::marker::Sync + core[a3bed6fa7f8910de]::marker::Send> as core[a3bed6fa7f8910de]::ops::function::Fn<(&std[faaa1722a6c2e07a]::panic::PanicHookInfo,)>>::call
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/alloc/src/boxed.rs:2333:9
  13:     0xff1ef2fe8130 - std[faaa1722a6c2e07a]::panicking::panic_with_hook
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:823:13
  14:     0xff1ef2fc83f4 - std[faaa1722a6c2e07a]::panicking::panic_handler::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:681:13
  15:     0xff1ef2fc0520 - std[faaa1722a6c2e07a]::sys::backtrace::__rust_end_short_backtrace::<std[faaa1722a6c2e07a]::panicking::panic_handler::{closure#0}, !>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/backtrace.rs:182:18
  16:     0xff1ef2fc9c48 - __rustc[a25a212e9fab2cd3]::rust_begin_unwind
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:679:5
  17:     0xff1eef639bfc - core[a3bed6fa7f8910de]::panicking::panic_fmt
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/panicking.rs:80:14
  18:     0xff1eef639bd4 - core[a3bed6fa7f8910de]::panicking::panic
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/panicking.rs:150:5
  19:     0xff1eef639908 - core[a3bed6fa7f8910de]::option::unwrap_failed
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/option.rs:2251:5
  20:     0xff1ef1447d84 - rustc_lint[5d8010d553e09163]::foreign_modules::name_of_extern_decl
  21:     0xff1ef14498d0 - rustc_lint[5d8010d553e09163]::foreign_modules::clashing_extern_declarations
  22:     0xff1ef121a7a4 - rustc_query_impl[75f7ded4abce79f5]::query_impl::clashing_extern_declarations::invoke_provider_fn::__rust_begin_short_backtrace
  23:     0xff1ef10bbde8 - <std[faaa1722a6c2e07a]::thread::local::LocalKey<core[a3bed6fa7f8910de]::cell::Cell<*const ()>>>::with::<rustc_middle[ff4e3d3446a5eafc]::ty::context::tls::enter_context<rustc_query_impl[75f7ded4abce79f5]::execution::execute_job_non_incr<rustc_middle[ff4e3d3446a5eafc]::query::caches::SingleCache<rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>>::{closure#0}, rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>::{closure#0}, rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>
  24:     0xff1ef0fced88 - rustc_query_impl[75f7ded4abce79f5]::execution::try_execute_query::<rustc_middle[ff4e3d3446a5eafc]::query::caches::SingleCache<rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>, false>
  25:     0xff1ef12d5bac - rustc_query_impl[75f7ded4abce79f5]::query_impl::clashing_extern_declarations::execute_query_non_incr::__rust_end_short_backtrace
  26:     0xff1eef931dd4 - rustc_interface[5e735bd0272d27ec]::passes::analysis::{closure#0}::{closure#0}::{closure#3}
  27:     0xff1ef2f77f20 - rustc_data_structures[81c4a32698bb0a71]::sync::parallel::par_fns
  28:     0xff1eef932848 - rustc_interface[5e735bd0272d27ec]::passes::analysis::{closure#0}::{closure#0}
  29:     0xff1ef2f77f20 - rustc_data_structures[81c4a32698bb0a71]::sync::parallel::par_fns
  30:     0xff1eef92c554 - <rustc_session[83eec55e1416d174]::session::Session>::time::<(), rustc_interface[5e735bd0272d27ec]::passes::analysis::{closure#0}>
  31:     0xff1eef8a8370 - rustc_interface[5e735bd0272d27ec]::passes::analysis
  32:     0xff1ef128be9c - rustc_query_impl[75f7ded4abce79f5]::query_impl::analysis::invoke_provider_fn::__rust_begin_short_backtrace
  33:     0xff1ef10bbde8 - <std[faaa1722a6c2e07a]::thread::local::LocalKey<core[a3bed6fa7f8910de]::cell::Cell<*const ()>>>::with::<rustc_middle[ff4e3d3446a5eafc]::ty::context::tls::enter_context<rustc_query_impl[75f7ded4abce79f5]::execution::execute_job_non_incr<rustc_middle[ff4e3d3446a5eafc]::query::caches::SingleCache<rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>>::{closure#0}, rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>::{closure#0}, rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>
  34:     0xff1ef0fced88 - rustc_query_impl[75f7ded4abce79f5]::execution::try_execute_query::<rustc_middle[ff4e3d3446a5eafc]::query::caches::SingleCache<rustc_middle[ff4e3d3446a5eafc]::query::erase::ErasedData<[u8; 0usize]>>, false>
  35:     0xff1ef12d6314 - rustc_query_impl[75f7ded4abce79f5]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  36:     0xff1eef6b6ae8 - <std[faaa1722a6c2e07a]::thread::local::LocalKey<core[a3bed6fa7f8910de]::cell::Cell<*const ()>>>::with::<rustc_middle[ff4e3d3446a5eafc]::ty::context::tls::enter_context<<rustc_middle[ff4e3d3446a5eafc]::ty::context::GlobalCtxt>::enter<rustc_interface[5e735bd0272d27ec]::passes::create_and_enter_global_ctxt<core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>, rustc_driver_impl[7b725a2f7bf77b9a]::run_compiler::{closure#0}::{closure#1}>::{closure#2}, core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>>::{closure#1}, core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>>::{closure#0}, core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>>
  37:     0xff1eef665844 - <rustc_middle[ff4e3d3446a5eafc]::ty::context::TyCtxt>::create_global_ctxt::<core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>, rustc_interface[5e735bd0272d27ec]::passes::create_and_enter_global_ctxt<core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>, rustc_driver_impl[7b725a2f7bf77b9a]::run_compiler::{closure#0}::{closure#1}>::{closure#2}>
  38:     0xff1eef705a00 - rustc_interface[5e735bd0272d27ec]::passes::create_and_enter_global_ctxt::<core[a3bed6fa7f8910de]::option::Option<rustc_interface[5e735bd0272d27ec]::queries::Linker>, rustc_driver_impl[7b725a2f7bf77b9a]::run_compiler::{closure#0}::{closure#1}>
  39:     0xff1eef6a2b24 - std[faaa1722a6c2e07a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5e735bd0272d27ec]::util::run_in_thread_with_globals<rustc_interface[5e735bd0272d27ec]::util::run_in_thread_pool_with_globals<rustc_interface[5e735bd0272d27ec]::interface::run_compiler<(), rustc_driver_impl[7b725a2f7bf77b9a]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  40:     0xff1eef6ced28 - <std[faaa1722a6c2e07a]::thread::lifecycle::spawn_unchecked<rustc_interface[5e735bd0272d27ec]::util::run_in_thread_with_globals<rustc_interface[5e735bd0272d27ec]::util::run_in_thread_pool_with_globals<rustc_interface[5e735bd0272d27ec]::interface::run_compiler<(), rustc_driver_impl[7b725a2f7bf77b9a]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[a3bed6fa7f8910de]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0xff1ef2ff3058 - <alloc[7220a3968fb26a7c]::boxed::Box<dyn core[a3bed6fa7f8910de]::ops::function::FnOnce<(), Output = ()> + core[a3bed6fa7f8910de]::marker::Send> as core[a3bed6fa7f8910de]::ops::function::FnOnce<()>>::call_once
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/alloc/src/boxed.rs:2319:9
  42:     0xff1ef2ff3058 - <std[faaa1722a6c2e07a]::sys::thread::unix::Thread>::new::thread_start
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/thread/unix.rs:123:17
  43:     0xff1eeea8b9f4 - <unknown>
  44:     0xff1eeeaf700c - <unknown>
---

note: compiler flags: --crate-type bin

query stack during panic:
#0 [clashing_extern_declarations] checking `extern fn` declarations are compatible
#1 [analysis] running analysis passes on crate `rust_out`
end of query stack
warning: 1 warning emitted

Couldn't compile the test.

bjorn3 added 4 commits July 24, 2026 11:53

Lower #[no_mangle] to #[symbol_name]/#[link_name]

999d08b

This reduces the amount of special casing #[no_mangle] needs in the rest of the compiler.

Change foreign_item_symbol_aliases to an Option

d7efef3

bjorn3 mentioned this pull request Jul 24, 2026

Use EII for #[panic_handler] #159016

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Rename symbols rather than add symbol aliases for EIIs when possible#159843

Rename symbols rather than add symbol aliases for EIIs when possible#159843
bjorn3 wants to merge 4 commits into
rust-lang:mainfrom
bjorn3:eii_using_symbol_rename

bjorn3 commented Jul 24, 2026

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bjorn3 commented Jul 24, 2026

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rust-log-analyzer commented Jul 24, 2026

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