Symbols are not demangled properly with -Csymbol-mangling-version=v0

[bobrik]

See: https://doc.rust-lang.org/rustc/symbol-mangling/v0.html

With default demangling:

With RUSTFLAGS=-Csymbol-mangling-version=v0:

That's on macOS, so dtrace based profiling.

There's a crate that supports better demangling: https://github.com/luser/rustfilt

[bobrik]

My best guess: by default dtrace does an equivalent of c++filt, which just doesn't understand v0 mangling:

$ echo 'requests-5d17f3a5c1ea5a42`_RNCNvXs0_NtCshIpxUpB4cO7_3fl29lifecycleINtB7_14FL2RequestHookNtB9_6FL2AppEINtNtNtCsirrfZNuT3Ck_7oxy_api12pub_wrappers5hooks15HttpRequestHookBX_E21handle_client_request0B9_' | c++filt
requests-5d17f3a5c1ea5a42`_RNCNvXs0_NtCshIpxUpB4cO7_3fl29lifecycleINtB7_14FL2RequestHookNtB9_6FL2AppEINtNtNtCsirrfZNuT3Ck_7oxy_api12pub_wrappers5hooks15HttpRequestHookBX_E21handle_client_request0B9_

Compare to rustfilt:

$ echo 'requests-5d17f3a5c1ea5a42`_RNCNvXs0_NtCshIpxUpB4cO7_3fl29lifecycleINtB7_14FL2RequestHookNtB9_6FL2AppEINtNtNtCsirrfZNuT3Ck_7oxy_api12pub_wrappers5hooks15HttpRequestHookBX_E21handle_client_request0B9_' | rustfilt
requests-5d17f3a5c1ea5a42`<fl2::lifecycle::FL2RequestHook<fl2::FL2App> as oxy_api::pub_wrappers::hooks::HttpRequestHook<fl2::FL2App>>::handle_client_request::{closure#0}

Outside of cargo flamegraph with perf we normally request --no-demangle and pipe through rustfilt and then c++filt for a good measure, which seems to work well. I'm not sure if c++filt is necessary, rustfilt might be sufficient.

[djc]

Open to review a PR for this if it belongs in flamegraph, maybe it belongs in inferno instead?

[bobrik]

I think demangling should happen before stack collapsing, so it belongs here. @jonhoo, what do you think?

[jonhoo]

Hmm, so, inferno doesn't demangle internally — we even explicitly removed support for that ages ago in jonhoo/inferno#144. See also jonhoo/inferno#180 (comment). It generally expects that whatever tool produces the input to the stack collapser does the demangling.

[djc]

Fair enough.

[bobrik]

I opened #363 to take care of this.