Support Rust v0 mangling

[ChoKyuWon]

For now, utils/demangle.c only care about the Itanium C++ ABI mangling rules.
However, Rust introduces a new mangling rule, v0 mangling. (See the RFC and PR)

For example, std::mem::align_of::<f64> mangles to _RINvNtC3std3mem8align_ofdE.
Note that this new mangling scheme starts with a new identifier, _R.

We need support for this new mangling scheme.

[namhyung]

What's the command line to enable the v0 mangling? It'd be nice if you share a result of uftrace + hello world in v0.

[ChoKyuWon]

$ cargo new --bin v0_mangling && cd v0_mangling
$ RUSTFLAGS="-Zsymbol-mangling-version=v0" cargo build

$ uftrace -P. -F _RNvCskxQuv2bvxbZ_11v0_mangling4main ./target/debug/v0_mangling
# DURATION     TID     FUNCTION
            [3613655] | _RNvCskxQuv2bvxbZ_11v0_mangling4main() {
   0.120 us [3613655] |   _RNvMs2_NtCscoN4IID3Vv4_4core3fmtNtB5_9Arguments6new_v1CskxQuv2bvxbZ_11v0_mangling();
            [3613655] |   std::io::stdio::_print() {
            [3613655] |     std::sync::once::Once::call_inner() {
            [3613655] |       std::sync::once::Once::call_once_force::_{{closure}}() {
   0.090 us [3613655] |         __rdl_alloc();
   0.351 us [3613655] |       } /* std::sync::once::Once::call_once_force::_{{closure}} */
   0.090 us [3613655] |       _<std..sync..once..WaiterQueue as core..ops..drop..Drop>::drop();
   0.741 us [3613655] |     } /* std::sync::once::Once::call_inner */
            [3613655] |     _<&std..io..stdio..Stdout as std..io..Write>::write_fmt() {
   0.090 us [3613655] |       std::sys_common::remutex::current_thread_unique_ptr::X::__getit();
            [3613655] |       core::fmt::write() {
            [3613655] |         _<std..io..Write..write_fmt..Adapter<T> as core..fmt..Write>::write_str() {
            [3613655] |           _<std..io..buffered..linewritershim..LineWriterShim<W> as std..io..Write>::write_all() {
            [3613655] |             _<std..io..stdio..StdoutRaw as std..io..Write>::write_all() {
   6.954 us [3613655] |               std::io::Write::write_all();
   7.184 us [3613655] |             } /* _<std..io..stdio..StdoutRaw as std..io..Write>::write_all */
   7.464 us [3613655] |           } /* _<std..io..buffered..linewritershim..LineWriterShim<W> as std..io..Write>::write_all */
   7.675 us [3613655] |         } /* _<std..io..Write..write_fmt..Adapter<T> as core..fmt..Write>::write_str */
   7.855 us [3613655] |       } /* core::fmt::write */
   8.235 us [3613655] |     } /* _<&std..io..stdio..Stdout as std..io..Write>::write_fmt */
   9.268 us [3613655] |   } /* std::io::stdio::_print */
  10.591 us [3613655] | } /* _RNvCskxQuv2bvxbZ_11v0_mangling4main */

$ uftrace -P. -F v0_mangling::main ./target/debug/v0_mangling
# DURATION     TID     FUNCTION
            [3613773] | main() {
            [3613773] |   _RINvNtCsjaRYnC5jcmR_3std2rt10lang_startuECskxQuv2bvxbZ_11v0_mangling() {
            [3613773] |     std::rt::lang_start_internal() {
            [3613773] |       std::rt::init() {
            [3613773] |         std::sys::unix::init() {
            [3613773] |           std::sys::unix::stack_overflow::imp::init() {
   2.365 us [3613773] |             std::sys::unix::stack_overflow::imp::make_handler();
   3.447 us [3613773] |           } /* std::sys::unix::stack_overflow::imp::init */
   8.336 us [3613773] |         } /* std::sys::unix::init */
  54.595 us [3613773] |         std::sys::unix::thread::guard::init();
            [3613773] |         _<&str as alloc..ffi..c_str..CString..new..SpecNewImpl>::spec_new_impl() {
   0.220 us [3613773] |           __rdl_alloc();
   0.130 us [3613773] |           alloc::vec::Vec<T,A>::into_boxed_slice();
   0.871 us [3613773] |         } /* _<&str as alloc..ffi..c_str..CString..new..SpecNewImpl>::spec_new_impl */
            [3613773] |         alloc::sync::Arc<T>::new_uninit() {
   0.110 us [3613773] |           __rdl_alloc();
   0.331 us [3613773] |         } /* alloc::sync::Arc<T>::new_uninit */
            [3613773] |         std::thread::local::LocalKey<T>::with() {
   0.471 us [3613773] |           std::sys_common::thread_info::THREAD_INFO::__getit();
   0.651 us [3613773] |         } /* std::thread::local::LocalKey<T>::with */
  65.405 us [3613773] |       } /* std::rt::init */
            [3613773] |       _RNCINvNtCsjaRYnC5jcmR_3std2rt10lang_startuE0CskxQuv2bvxbZ_11v0_mangling() {
            [3613773] |         _RINvNtNtCsjaRYnC5jcmR_3std10sys_common9backtrace28___rust_begin_short_backtraceFEuuECskxQuv2bvxbZ_11v0_mangling() {
            [3613773] |           _RNvYFEuINtNtNtCscoN4IID3Vv4_4core3ops8function6FnOnceuE9call_onceCskxQuv2bvxbZ_11v0_mangling() {
            [3613773] |             _RNvCskxQuv2bvxbZ_11v0_mangling4main() {
...

[namhyung]

I've pushed review/rust-demangle-v1 branch for the v0 format. The implementation is based on the Rust doc

$ cat input.txt
_RINvNtCsjaRYnC5jcmR_3std2rt10lang_startuECskxQuv2bvxbZ_11v0_mangling
_RNCINvNtCsjaRYnC5jcmR_3std2rt10lang_startuE0CskxQuv2bvxbZ_11v0_mangling
_RINvNtNtCsjaRYnC5jcmR_3std10sys_common9backtrace28___rust_begin_short_backtraceFEuuECskxQuv2bvxbZ_11v0_mangling
_RNvYFEuINtNtNtCscoN4IID3Vv4_4core3ops8function6FnOnceuE9call_onceCskxQuv2bvxbZ_11v0_mangling
_RNvCskxQuv2bvxbZ_11v0_mangling4main

$ cat input.txt | misc/demangler
std::rt::lang_start<()>
std::rt::lang_start<()>::{closure}
std::sys_common::backtrace::__rust_begin_short_backtrace<fn(),()>
<fn()>::call_once
v0_mangling::main

$ cat input.txt | c++filt
std[df58d1607babe273]::rt::lang_start::<()>
std[df58d1607babe273]::rt::lang_start::<()>::{closure#0}
std[df58d1607babe273]::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
<fn() as core[906dcb38ebedb744]::ops::function::FnOnce<()>>::call_once
v0_mangling[ef4f9b50eed7c9a5]::main

[namhyung]

Pushed review/rust-demangle-v2 branch.

• Fix a bug in base62 decoder
• Fix an error in tuple type dyn trait handling
• Add a new unit test for base62 decoding

Now it seems to be able to demangle all symbols in cargo.

Before:

$ uftrace -P. --report -- cargo --version
cargo 1.94.1 (29ea6fb6a 2026-03-24) (Fedora 1.94.1-1.fc43)
#
# uftrace report
#
  Total time   Self time       Calls  Function
  ==========  ==========  ==========  ====================
    1.912 ms  146.691 us           1  std::rt::lang_start_internal
    1.748 ms    8.134 us           1  _RNvCsf1z8G7XPNsX_5cargo4main
  757.529 us    7.827 us           1  _RNvNtCsf1z8G7XPNsX_5cargo3cli3cli
  629.898 us   73.749 us           1  _RNvNtCsf1z8G7XPNsX_5cargo8commands7builtin
  337.606 us   68.934 us          46  _RINvNtCs1EZQAllfVpG_4core3ptr13drop_in_placeNtNtNtCs7QfNEe7ub1A_12clap_builder7builder7command7CommandECsf1z8G7XPNsX_5cargo
  275.579 us    0.978 us           1  _RNvMNtNtCseQ5aOgbVAxM_5cargo4util7contextNtB2_13GlobalContext7default
  262.712 us  124.340 us        1009  _RINvNtCs1EZQAllfVpG_4core3ptr13drop_in_placeNtNtNtCs7QfNEe7ub1A_12clap_builder7builder3arg3ArgECsf1z8G7XPNsX_5cargo
  244.470 us   36.963 us           1  _RNvMNtNtCseQ5aOgbVAxM_5cargo4util7contextNtB2_13GlobalContext3new
  207.122 us    1.265 us           1  _RNvMs3_NtNtCs7QfNEe7ub1A_12clap_builder7builder7commandNtB5_7Command9__do_parse
  184.503 us   52.417 us           3  _RNvMs_NtNtNtCseQ5aOgbVAxM_5cargo4util7context2deNtB4_15ConfigMapAccess10new_struct
  147.663 us   41.286 us           1  _RNvMs3_NtNtCs7QfNEe7ub1A_12clap_builder7builder7commandNtB5_7Command11__build_self
  132.240 us   14.396 us         134  _RNvMs1_NtCs9rZxOlQsGp9_9hashbrown3mapINtB5_7HashMapNtNtCs4AfZbDHWQAq_5alloc6string6StringBN_NtNtNtCs89T1blTxxU8_3std4hash6random11RandomStateE6insertCseQ5aOgbVAxM_5cargo
  129.077 us   68.374 us        1110  _RINvNtCs1EZQAllfVpG_4core3ptr13drop_in_placeINtNtCs4AfZbDHWQAq_5alloc3vec3VecNtNtNtCs7QfNEe7ub1A_12clap_builder4util9any_value8AnyValueEECsf1z8G7XPNsX_5cargo
  124.957 us   80.748 us         625  _RINvNvMs2_NtCs4AfZbDHWQAq_5alloc7raw_vecINtB8_11RawVecInnerpE7reserve21do_reserve_and_handleNtNtBa_5alloc6GlobalECs7QfNEe7ub1A_12clap_builder.llvm.9431986496177942022
  104.839 us  104.839 us        1319  _RNvMs4_NtCs4AfZbDHWQAq_5alloc7raw_vecNtB5_11RawVecInner11finish_growCs7QfNEe7ub1A_12clap_builder.llvm.9431986496177942022
  103.612 us   65.768 us         350  _RINvYNtNtNtCs89T1blTxxU8_3std4hash6random11RandomStateNtNtCs1EZQAllfVpG_4core4hash11BuildHasher8hash_oneRNtCsj4RelT2Xl0o_3url3UrlECseQ5aOgbVAxM_5cargo
   98.165 us   30.087 us         174  _RNvMNtNtCs7QfNEe7ub1A_12clap_builder4util8flat_mapINtB2_7FlatMapNtNtB4_9any_value10AnyValueIdNtB12_8AnyValueE6insertCsf1z8G7XPNsX_5cargo
   97.287 us    1.073 us           1  _RNvNtCsf1z8G7XPNsX_5cargo3cli14configure_gctx
   95.087 us    1.185 us           1  _RNvMNtNtCseQ5aOgbVAxM_5cargo4util7contextNtB2_13GlobalContext9configure
...

After:

$ uftrace -P. --report -- cargo --version
cargo 1.94.1 (29ea6fb6a 2026-03-24) (Fedora 1.94.1-1.fc43)
#
# uftrace report
#
  Total time   Self time       Calls  Function
  ==========  ==========  ==========  ====================
    2.412 ms  166.767 us           1  std::rt::lang_start_internal
    2.224 ms    9.777 us           1  cargo::main
  953.208 us    9.534 us           1  cargo::cli::cli
  796.101 us  100.227 us           1  cargo::commands::builtin
  445.594 us   89.868 us          46  core::ptr::drop_in_place<clap_builder::builder::command::Command>
  348.268 us  172.604 us        1009  core::ptr::drop_in_place<clap_builder::builder::arg::Arg>
  337.026 us    1.382 us           1  <cargo::util::context::GlobalContext>::default
  297.483 us   44.737 us           1  <cargo::util::context::GlobalContext>::new
  262.128 us    1.806 us           1  <clap_builder::builder::command::Command>::_do_parse
  228.737 us   64.143 us           3  <cargo::util::context::de::ConfigMapAccess>::new_struct
  186.185 us   55.383 us           1  <clap_builder::builder::command::Command>::_build_self
  168.863 us  111.439 us         651  <alloc::raw_vec::RawVecInner<_>>::reserve::do_reserve_and_handle<alloc::alloc::Global>
  167.901 us   93.022 us        1124  core::ptr::drop_in_place<alloc::vec::Vec<clap_builder::util::any_value::AnyValue>>
  157.618 us   16.870 us         134  <hashbrown::map::HashMap<alloc::string::String,alloc::string::String,std::hash::random::RandomState>>::insert
  144.239 us  144.239 us        1382  <alloc::raw_vec::RawVecInner>::finish_grow
  126.804 us    1.692 us           1  cargo::cli::configure_gctx
  123.837 us    1.532 us           1  <cargo::util::context::GlobalContext>::configure
...