Please default "force-unwind-tables" to "yes" on Linux, so that unwind tables are present even if panic = "abort"

[mstange]

On Linux, binaries need to contain unwind tables if one wants to get useful and accurate stack traces in profilers, debuggers and crash reports,. This requirement is mostly due to the fact that the Rust compiler, by default, does not use frame pointers on Linux.

When panic is set to "unwind" (the default), the Rust compiler emits unwind tables for all functions. This is good.

However, when building with panic = "abort", the Rust compiler currently does not emit unwind tables for many functions. For example, a Linux x86_64 build of dump_syms with panic = "abort" has unwind tables for 5017 functions with the default settings, and for 9204 functions with -C force-unwind-tables=yes. The generated code for both builds is identical.

I think force-unwind-tables=yes would be a better default. It does not make the generated code any less efficient; it only generates extra information on the side. People who are concerned about binary size and who do not need useful stack traces can still make the trade-off and set -C force-unwind-tables=no.

This problem was also encountered in rust-lang/backtrace-rs#397 and in #81902.

[mstange]

@jrmuizel suggested I answer the following questions, to allow for a more informed decision:

• What is the default behavior for C++ code which is compiled with -fno-exceptions? Does clang emit unwind tables for leaf C++ function which don't throw any exceptions?
• For the functions without unwind tables, is the information only missing from .eh_frame or also from .debug_frame?

[e00E]

Repeating my comment from the linked issue right above this post because it shows some more motivation for this.

stable-x86_64-unknown-linux-gnu
rustc 1.69.0 (84c898d 2023-04-16

Consider the following rust program:

fn main() {
    foo();
}

fn foo() {
    bar();
}

fn bar() {
    assert_eq!(false, true);
}

This program panics. The call stack at the panic is bar <- foo <- main.

I am going to run this program while varying the -Cpanic argument like so:

rustc -Cpanic=unwind -Cdebuginfo=1 a.rs && env RUST_BACKTRACE=full ./a

With -Cpanic=unwind:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `false`,
 right: `true`', a.rs:10:5
stack backtrace:
   0:     0x555d9bd4c5aa - std::backtrace_rs::backtrace::libunwind::trace::ha9053a9a07ca49cb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x555d9bd4c5aa - std::backtrace_rs::backtrace::trace_unsynchronized::h9c2852a457ad564e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x555d9bd4c5aa - std::sys_common::backtrace::_print_fmt::h457936fbfaa0070f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x555d9bd4c5aa - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5779d7bf7f70cb0c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x555d9bd6620e - core::fmt::write::h5a4baaff1bcd3eb5
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/fmt/mod.rs:1232:17
   5:     0x555d9bd4a735 - std::io::Write::write_fmt::h4bc1f301cb9e9cce
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/io/mod.rs:1684:15
   6:     0x555d9bd4c375 - std::sys_common::backtrace::_print::h5fcdc36060f177e8
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x555d9bd4c375 - std::sys_common::backtrace::print::h54ca9458b876c8bf
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x555d9bd4d9cf - std::panicking::default_hook::{{closure}}::hbe471161c7664ed6
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:271:22
   9:     0x555d9bd4d70b - std::panicking::default_hook::ha3500da57aa4ac4f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:290:9
  10:     0x555d9bd4df78 - std::panicking::rust_panic_with_hook::h50c09d000dc561d2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:692:13
  11:     0x555d9bd4de79 - std::panicking::begin_panic_handler::{{closure}}::h9e2b2176e00e0d9c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:583:13
  12:     0x555d9bd4ca16 - std::sys_common::backtrace::__rust_end_short_backtrace::h5739b8e512c09d02
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:150:18
  13:     0x555d9bd4db82 - rust_begin_unwind
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
  14:     0x555d9bd34ed3 - core::panicking::panic_fmt::hf33a1475b4dc5c3e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
  15:     0x555d9bd3514f - core::panicking::assert_failed_inner::haf9816227b20b6f2
  16:     0x555d9bd356e6 - core::panicking::assert_failed::hfe4604f1e2156329
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:211:5
  17:     0x555d9bd355d2 - a::bar::h54068ed5e62eaea6
                               at /tmp/a/a.rs:10:5
  18:     0x555d9bd35586 - a::foo::hbe93c09168c5d787
                               at /tmp/a/a.rs:6:5
  19:     0x555d9bd35576 - a::main::hf778f5e35fefb56f
                               at /tmp/a/a.rs:2:5
  20:     0x555d9bd35503 - core::ops::function::FnOnce::call_once::h0cda876b3b6f352f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/ops/function.rs:250:5
  21:     0x555d9bd354e9 - std::sys_common::backtrace::__rust_begin_short_backtrace::hcd8ad9bf1b410bdc
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:134:18
  22:     0x555d9bd35659 - std::rt::lang_start::{{closure}}::h135e76f90c71d025
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:166:18
  23:     0x555d9bd48a6c - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hd6efcd3bec896f2c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/ops/function.rs:287:13
  24:     0x555d9bd48a6c - std::panicking::try::do_call::hce04e543bb1f4cbb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:487:40
  25:     0x555d9bd48a6c - std::panicking::try::h3342dd4e1f680968
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:451:19
  26:     0x555d9bd48a6c - std::panic::catch_unwind::h148ce1e59ac0cee7
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panic.rs:140:14
  27:     0x555d9bd48a6c - std::rt::lang_start_internal::{{closure}}::h25f9dda2057a67fe
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:148:48
  28:     0x555d9bd48a6c - std::panicking::try::do_call::h7caaaeaf9401650b
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:487:40
  29:     0x555d9bd48a6c - std::panicking::try::he7d15285746cbbc2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:451:19
  30:     0x555d9bd48a6c - std::panic::catch_unwind::h89fb4f50c0301fe0
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panic.rs:140:14
  31:     0x555d9bd48a6c - std::rt::lang_start_internal::h078acd489417d3c1
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:148:20
  32:     0x555d9bd35637 - std::rt::lang_start::h123fe1c2f5ee3bc1
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:165:17
  33:     0x555d9bd355fe - main
  34:     0x7f78e854c850 - <unknown>
  35:     0x7f78e854c90a - __libc_start_main
  36:     0x555d9bd35405 - _start
  37:                0x0 - <unknown>

With -Cpanic=abort:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `false`,
 right: `true`', a.rs:10:5
stack backtrace:
   0:     0x557cb620a58a - std::backtrace_rs::backtrace::libunwind::trace::ha9053a9a07ca49cb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x557cb620a58a - std::backtrace_rs::backtrace::trace_unsynchronized::h9c2852a457ad564e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x557cb620a58a - std::sys_common::backtrace::_print_fmt::h457936fbfaa0070f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x557cb620a58a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5779d7bf7f70cb0c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x557cb6223d9e - core::fmt::write::h5a4baaff1bcd3eb5
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/fmt/mod.rs:1232:17
   5:     0x557cb6208715 - std::io::Write::write_fmt::h4bc1f301cb9e9cce
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/io/mod.rs:1684:15
   6:     0x557cb620a355 - std::sys_common::backtrace::_print::h5fcdc36060f177e8
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x557cb620a355 - std::sys_common::backtrace::print::h54ca9458b876c8bf
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x557cb620b76f - std::panicking::default_hook::{{closure}}::hbe471161c7664ed6
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:271:22
   9:     0x557cb620b4ab - std::panicking::default_hook::ha3500da57aa4ac4f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:290:9
  10:     0x557cb620bd18 - std::panicking::rust_panic_with_hook::h50c09d000dc561d2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:692:13
  11:     0x557cb620bc19 - std::panicking::begin_panic_handler::{{closure}}::h9e2b2176e00e0d9c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:583:13
  12:     0x557cb620a9f6 - std::sys_common::backtrace::__rust_end_short_backtrace::h5739b8e512c09d02
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:150:18
  13:     0x557cb620b922 - rust_begin_unwind
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
  14:     0x557cb61f2ed3 - core::panicking::panic_fmt::hf33a1475b4dc5c3e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
  15:     0x557cb61f314f - core::panicking::assert_failed_inner::haf9816227b20b6f2
  16:     0x557cb61f36c6 - core::panicking::assert_failed::hfe4604f1e2156329
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:211:5

Now I am going to change the assert_eq to assert:

assert!(false == true, "expected {} == {} but they weren't", false, true);

With -Cpanic=unwind:

thread 'main' panicked at 'expected false == true but they weren't', a.rs:10:5
stack backtrace:
   0:     0x564f3069467a - std::backtrace_rs::backtrace::libunwind::trace::ha9053a9a07ca49cb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x564f3069467a - std::backtrace_rs::backtrace::trace_unsynchronized::h9c2852a457ad564e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x564f3069467a - std::sys_common::backtrace::_print_fmt::h457936fbfaa0070f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x564f3069467a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5779d7bf7f70cb0c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x564f306ae2de - core::fmt::write::h5a4baaff1bcd3eb5
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/fmt/mod.rs:1232:17
   5:     0x564f30692805 - std::io::Write::write_fmt::h4bc1f301cb9e9cce
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/io/mod.rs:1684:15
   6:     0x564f30694445 - std::sys_common::backtrace::_print::h5fcdc36060f177e8
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x564f30694445 - std::sys_common::backtrace::print::h54ca9458b876c8bf
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x564f30695a9f - std::panicking::default_hook::{{closure}}::hbe471161c7664ed6
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:271:22
   9:     0x564f306957db - std::panicking::default_hook::ha3500da57aa4ac4f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:290:9
  10:     0x564f30696048 - std::panicking::rust_panic_with_hook::h50c09d000dc561d2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:692:13
  11:     0x564f30695f49 - std::panicking::begin_panic_handler::{{closure}}::h9e2b2176e00e0d9c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:583:13
  12:     0x564f30694ae6 - std::sys_common::backtrace::__rust_end_short_backtrace::h5739b8e512c09d02
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:150:18
  13:     0x564f30695c52 - rust_begin_unwind
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
  14:     0x564f3067ced3 - core::panicking::panic_fmt::hf33a1475b4dc5c3e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
  15:     0x564f3067d5fd - a::bar::h54068ed5e62eaea6
                               at /tmp/a/a.rs:10:5
  16:     0x564f3067d576 - a::foo::hbe93c09168c5d787
                               at /tmp/a/a.rs:6:5
  17:     0x564f3067d566 - a::main::hf778f5e35fefb56f
                               at /tmp/a/a.rs:2:5
  18:     0x564f3067d503 - core::ops::function::FnOnce::call_once::h0cda876b3b6f352f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/ops/function.rs:250:5
  19:     0x564f3067d4e9 - std::sys_common::backtrace::__rust_begin_short_backtrace::hcd8ad9bf1b410bdc
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:134:18
  20:     0x564f3067d679 - std::rt::lang_start::{{closure}}::h135e76f90c71d025
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:166:18
  21:     0x564f30690b3c - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hd6efcd3bec896f2c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/ops/function.rs:287:13
  22:     0x564f30690b3c - std::panicking::try::do_call::hce04e543bb1f4cbb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:487:40
  23:     0x564f30690b3c - std::panicking::try::h3342dd4e1f680968
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:451:19
  24:     0x564f30690b3c - std::panic::catch_unwind::h148ce1e59ac0cee7
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panic.rs:140:14
  25:     0x564f30690b3c - std::rt::lang_start_internal::{{closure}}::h25f9dda2057a67fe
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:148:48
  26:     0x564f30690b3c - std::panicking::try::do_call::h7caaaeaf9401650b
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:487:40
  27:     0x564f30690b3c - std::panicking::try::he7d15285746cbbc2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:451:19
  28:     0x564f30690b3c - std::panic::catch_unwind::h89fb4f50c0301fe0
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panic.rs:140:14
  29:     0x564f30690b3c - std::rt::lang_start_internal::h078acd489417d3c1
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:148:20
  30:     0x564f3067d657 - std::rt::lang_start::h123fe1c2f5ee3bc1
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/rt.rs:165:17
  31:     0x564f3067d61e - main
  32:     0x7fbbad08d850 - <unknown>
  33:     0x7fbbad08d90a - __libc_start_main
  34:     0x564f3067d405 - _start
  35:                0x0 - <unknown>

With -Cpanic=abort:

thread 'main' panicked at 'expected false == true but they weren't', a.rs:10:5
stack backtrace:
   0:     0x5562f55a165a - std::backtrace_rs::backtrace::libunwind::trace::ha9053a9a07ca49cb
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x5562f55a165a - std::backtrace_rs::backtrace::trace_unsynchronized::h9c2852a457ad564e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x5562f55a165a - std::sys_common::backtrace::_print_fmt::h457936fbfaa0070f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x5562f55a165a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5779d7bf7f70cb0c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x5562f55bae6e - core::fmt::write::h5a4baaff1bcd3eb5
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/fmt/mod.rs:1232:17
   5:     0x5562f559f7e5 - std::io::Write::write_fmt::h4bc1f301cb9e9cce
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/io/mod.rs:1684:15
   6:     0x5562f55a1425 - std::sys_common::backtrace::_print::h5fcdc36060f177e8
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x5562f55a1425 - std::sys_common::backtrace::print::h54ca9458b876c8bf
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x5562f55a283f - std::panicking::default_hook::{{closure}}::hbe471161c7664ed6
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:271:22
   9:     0x5562f55a257b - std::panicking::default_hook::ha3500da57aa4ac4f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:290:9
  10:     0x5562f55a2de8 - std::panicking::rust_panic_with_hook::h50c09d000dc561d2
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:692:13
  11:     0x5562f55a2ce9 - std::panicking::begin_panic_handler::{{closure}}::h9e2b2176e00e0d9c
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:583:13
  12:     0x5562f55a1ac6 - std::sys_common::backtrace::__rust_end_short_backtrace::h5739b8e512c09d02
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/sys_common/backtrace.rs:150:18
  13:     0x5562f55a29f2 - rust_begin_unwind
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
  14:     0x5562f5589ed3 - core::panicking::panic_fmt::hf33a1475b4dc5c3e
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
  15:     0x5562f558a5dd - a::bar::h54068ed5e62eaea6
                               at /tmp/a/a.rs:10:5
  16:     0x5562f558a556 - a::foo::hbe93c09168c5d787
                               at /tmp/a/a.rs:6:5
  17:     0x5562f558a546 - a::main::hf778f5e35fefb56f
                               at /tmp/a/a.rs:2:5
  18:     0x5562f558a503 - core::ops::function::FnOnce::call_once::h0cda876b3b6f352f
                               at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/ops/function.rs:250:5

---

The part of the backtrace that is meaningful is the bar <- foo <- main relation. This part was found in all configurations except when using -Cpanic=abort with assert_eq. This is a bug because as evidenced by the other backtraces, main, foo, and bar are part of the call stack at this point. Yet they are not printed. Even when accepting that asserts might print incorrect backtraces in an abort configuration (which I don't), it is still separately unexpected that the backtrace is only incorrect with assert_eq but not with assert.