Very confusing error message when panicking during a panic #114954
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A-panic
Area: Panicking machinery
C-bug
Category: This is a bug.
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cc @RalfJung |
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Mmmm, actually this doesn't have anything to do with miri. Simply executing this code produces |
SUPERCILEX
changed the title
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This changed in 1.71: 1.70.0 output: 1.71.0 output: 1.71.0 stabilized C-unwind in #106075 (feature tracked in #74990), and that's what I expect this change to bisect to (though I haven't done any actual bisection) It would be nice if the old message could be restored, the message "thread panicked while panicking. aborting." is significantly more clear. The extra backtrace also isn't super nice. |
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A combination of those error messages would be great too. |
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"cannot unwind" here means "is not allowed to unwind". And as you say this error does not come from Miri, it comes from the standard library.
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Currently the compiler does not differentiate between an unwind in a landing pad (recursive panic) and an unwind from a function that cannot unwind ( |
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Well, unwind in a landing pad itself doesn't show that same error. It's the double-panic that triggers the error. Here's the full error: Having 2 stacktraces is already somewhat strange. And doesn't the panic machinery know that a panic-while-panicking occurred, so that it can print that? |
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That's a
The panic machinery can't determine that on its own, because this code is perfectly valid and shouldn't abort at the point of the inner panic, it should continue unwinding normally: struct Double;
impl Drop for Double {
fn drop(&mut self) {
// 2 panics are active at once, but this is fine since it is caught.
std::panic::catch_unwind(|| panic!("twice"));
}
}
let _d = Double;
panic!("once"); |
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Hm, I guess what happens is that the So to fix that we'd probably need some sort of |
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And then the 2nd backtrace occurs because rust/library/std/src/panicking.rs Lines 247 to 253 in d06ca0f That's probably also undesirable for this case. |
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There is some value in having a backtrace here since it shows you which function on the stack was no-unwind. But I agree that in practice this has rather limited value. |
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We should definitely print the backtrace on |
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When adding such a Cc @bjorn3 |
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Adding a string argument would increase binary sizes as the string would be duplicated for every codegen unit that calls it. Using two separate functions would only codegen the functions + strings once in libcore. |
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Considering that there are a limited number of possible reasons, it would be better for code size to have a specific entry point for each reason. |
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Doesn't LLVM deduplicate the strings?
I am a little surprised because Assert terminators are very common and they don't have any optimizations like that.
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Linkers can deduplicate C strings when marking the global as being a deduplicatable C string, however this requires the strings to be nul-terminated and not have any interior nul byte as they will split the section with the C strings on nul bytes to find the individual strings. There is also COMDAT which someone is trying to implement in rustc right now, but the current version of that PR seems to have the complete opposite effect and increase the binary size and make linking much slower: #114816 |
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when terminating during unwinding, show the reason why
With this, the output on double-panic becomes something like that:
```
thread 'main' panicked at src/tools/miri/tests/fail/panic/double_panic.rs:15:5:
first
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at src/tools/miri/tests/fail/panic/double_panic.rs:10:9:
second
stack backtrace:
0: 0xbe273a - std::backtrace_rs::backtrace::miri::trace_unsynchronized::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:99:5
1: 0xbe22e6 - std::backtrace_rs::backtrace::miri::trace::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:62:14
2: 0xbe1086 - std::backtrace_rs::backtrace::trace_unsynchronized::<[closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
3: 0xba3afd - std::sys_common::backtrace::_print_fmt
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:67:5
4: 0xba2471 - <std::sys_common::backtrace::_print::DisplayBacktrace as std::fmt::Display>::fmt
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:44:22
5: 0xbcf754 - core::fmt::rt::Argument::<'_>::fmt
at /home/r/src/rust/rustc.3/library/core/src/fmt/rt.rs:138:9
6: 0x9b8f81 - std::fmt::write
at /home/r/src/rust/rustc.3/library/core/src/fmt/mod.rs:1094:17
7: 0x21391d - <std::sys::unix::stdio::Stderr as std::io::Write>::write_fmt
at /home/r/src/rust/rustc.3/library/std/src/io/mod.rs:1714:15
8: 0xba37b1 - std::sys_common::backtrace::_print
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:47:5
9: 0xba365b - std::sys_common::backtrace::print
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:34:9
10: 0x143c67 - std::panic_hook_with_disk_dump::{closure#1}
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:278:22
11: 0x144187 - std::panic_hook_with_disk_dump
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:312:9
12: 0x143659 - std::panicking::default_hook
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:239:5
13: 0x1482a7 - std::panicking::rust_panic_with_hook
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:729:13
14: 0x1475d5 - std::rt::begin_panic::<&str>::{closure#0}
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:650:9
15: 0xba496a - std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::rt::begin_panic<&str>::{closure#0}], !>
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:170:18
16: 0x147599 - std::rt::begin_panic::<&str>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:649:12
17: 0x31916 - <Foo as std::ops::Drop>::drop
at src/tools/miri/tests/fail/panic/double_panic.rs:10:9
18: 0x1a2b5e - std::ptr::drop_in_place::<Foo> - shim(Some(Foo))
at /home/r/src/rust/rustc.3/library/core/src/ptr/mod.rs:497:1
19: 0x202bf - main
at src/tools/miri/tests/fail/panic/double_panic.rs:16:1
20: 0xcc6a8 - <fn() as std::ops::FnOnce<()>>::call_once - shim(fn())
at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:250:5
21: 0xba47d9 - std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:154:18
22: 0x141a6a - std::rt::lang_start::<()>::{closure#0}
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:166:18
23: 0xcca18 - std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once
at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:284:13
24: 0x146469 - std::panicking::try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
25: 0x145e09 - std::panicking::try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
26: 0x7b0ac - std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
27: 0x14189b - std::rt::lang_start_internal::{closure#2}
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:48
28: 0x146481 - std::panicking::try::do_call::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
29: 0x145e2c - std::panicking::try::<isize, [closure@std::rt::lang_start_internal::{closure#2}]>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
30: 0x7b0d5 - std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
31: 0x1418b0 - std::rt::lang_start_internal
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:20
32: 0x141a97 - std::rt::lang_start::<()>
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:165:17
thread 'main' panicked at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:126:5:
panic in a destructor during cleanup
stack backtrace:
0: 0xe9f6d7 - std::backtrace_rs::backtrace::miri::trace_unsynchronized::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:99:5
1: 0xe9f27d - std::backtrace_rs::backtrace::miri::trace::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:62:14
2: 0xe9e016 - std::backtrace_rs::backtrace::trace_unsynchronized::<[closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
3: 0xba3afd - std::sys_common::backtrace::_print_fmt
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:67:5
4: 0xba2471 - <std::sys_common::backtrace::_print::DisplayBacktrace as std::fmt::Display>::fmt
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:44:22
5: 0xbcf754 - core::fmt::rt::Argument::<'_>::fmt
at /home/r/src/rust/rustc.3/library/core/src/fmt/rt.rs:138:9
6: 0x9b8f81 - std::fmt::write
at /home/r/src/rust/rustc.3/library/core/src/fmt/mod.rs:1094:17
7: 0x4d0895 - <std::sys::unix::stdio::Stderr as std::io::Write>::write_fmt
at /home/r/src/rust/rustc.3/library/std/src/io/mod.rs:1714:15
8: 0xba37b1 - std::sys_common::backtrace::_print
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:47:5
9: 0xba365b - std::sys_common::backtrace::print
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:34:9
10: 0x400bd4 - std::panic_hook_with_disk_dump::{closure#1}
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:278:22
11: 0x144187 - std::panic_hook_with_disk_dump
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:312:9
12: 0x143659 - std::panicking::default_hook
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:239:5
13: 0x1482a7 - std::panicking::rust_panic_with_hook
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:729:13
14: 0x40403b - std::panicking::begin_panic_handler::{closure#0}
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:619:13
15: 0xe618b3 - std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::panicking::begin_panic_handler::{closure#0}], !>
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:170:18
16: 0x403fc8 - std::panicking::begin_panic_handler
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:617:5
17: 0xee23e9 - core::panicking::panic_nounwind_fmt
at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:96:14
18: 0xee29e6 - core::panicking::panic_nounwind
at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:126:5
19: 0xee365e - core::panicking::panic_in_cleanup
at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:206:5
20: 0x2028a - main
at src/tools/miri/tests/fail/panic/double_panic.rs:13:1
21: 0x3895ee - <fn() as std::ops::FnOnce<()>>::call_once - shim(fn())
at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:250:5
22: 0xe61725 - std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:154:18
23: 0x3fe9aa - std::rt::lang_start::<()>::{closure#0}
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:166:18
24: 0x389962 - std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once
at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:284:13
25: 0x4033b9 - std::panicking::try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
26: 0x402d58 - std::panicking::try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
27: 0x337ff7 - std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
28: 0x3fe7e7 - std::rt::lang_start_internal::{closure#2}
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:48
29: 0x4033d6 - std::panicking::try::do_call::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
30: 0x402d7f - std::panicking::try::<isize, [closure@std::rt::lang_start_internal::{closure#2}]>
at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
31: 0x338028 - std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
32: 0x1418b0 - std::rt::lang_start_internal
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:20
33: 0x3fe9dc - std::rt::lang_start::<()>
at /home/r/src/rust/rustc.3/library/std/src/rt.rs:165:17
thread caused non-unwinding panic. aborting.
```
If we also land rust-lang/rust#115020, the 2nd backtrace disappears, hopefully making the "panic in a destructor during cleanup" easier to see.
Fixes rust-lang/rust#114954.
GuillaumeGomez
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…trace, r=Amanieu avoid triple-backtrace due to panic-during-cleanup Supersedes rust-lang#115020 Cc rust-lang#114954 r? `@Amanieu`
matthiaskrgr
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…trace, r=Amanieu avoid triple-backtrace due to panic-during-cleanup Supersedes rust-lang#115020 Cc rust-lang#114954 r? ``@Amanieu``
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…Amanieu avoid triple-backtrace due to panic-during-cleanup Supersedes rust-lang/rust#115020 Cc rust-lang/rust#114954 r? ``@Amanieu``
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I tried this code:
Clearly the function panics so the error message doesn't make much sense. I believe it's saying that while panicking, the function is placed into a context in which nested panics are disallowed. Perhaps the message could include a hint that says something like
Possibly caused by nested panics from a drop function.The text was updated successfully, but these errors were encountered: