[Bug gdb/29735] New: Can't have multiple breakpoints - crash otherwise

[Bug gdb/29735] New: Can't have multiple breakpoints - crash otherwise

[amab8901 at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

            Bug ID: 29735
           Summary: Can't have multiple breakpoints - crash otherwise
           Product: gdb
           Version: 12.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: amab8901 at protonmail dot com
  Target Milestone: ---

I wrote the following code:

```
use fst::{Set};
use fst::automaton::Levenshtein;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let keys = vec!["hej"];
    let set = Set::from_iter(keys)?;

    let lev = Levenshtein::new("foo", 1)?;

    println!("{:#?}", set);
    println!("{:#?}", lev);
    Ok(())
}
```

This code crashes when attempting to run this line:
```
let lev = Levenshtein::new("foo", 1)?;
```

Here is the `Cargo.toml`:
```
[package]
name = "playground"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at
https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
fst = { version = "0.4.7", features = ["levenshtein"] }
```
How to reproduce:
1. `cargo new playground`
2. enter project's root directory
3. `cargo add fst --features=levenshtein`
4. `nvim .` (note: I have NerdTree extension in my Neovim)
5. Navigate into `main.rs` file via NerdTree
6. Replace the `main.rs` content with:
```
use fst::{Set};
use fst::automaton::Levenshtein;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let keys = vec!["hej"];
    let set = Set::from_iter(keys)?;

    let lev = Levenshtein::new("foo", 1)?;

    println!("{:#?}", set);
    println!("{:#?}", lev);
    Ok(())
```
7. `:w` in neovim
8. `:! cargo build` in neovim (note that bash is in project's root folder while
neovim is simultaneously in `main.rs` at this point)
9. Open another terminal in project's root folder
10. In the new terminal, run `gdb target/debug/playground` (alternatively:
`rust-gdb target/debug/playground`)
11. In gdb, run the following commands, one line at a time (note that I have
[GDB Dashboard](https://github.com/cyrus-and/gdb-dashboard) implemented into my
GDB):
```
list
b 8 
b 10
list
b 11
b 12
r
c
```
It crashes as soon as you enter `c`. The following specified what "crash" means
and shows the output that I see:

```
Breakpoint 2, playground::main () at src/main.rs:10
10          println!("{:#?}", set);
../../gdb/gdbtypes.h:1064: internal-error: field: Assertion `idx >= 0 && idx <
num_fields ()' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
----- Backtrace -----
0x5654d0133b6b ???
0x5654d0471d44 ???
0x5654d0534ce3 ???
0x5654d00b3ea1 ???
0x5654d0483e23 ???
0x5654d03b74bc ???
0x5654d047f0db ???
0x5654d0484935 ???
0x5654d0485b6b ???
0x5654d03b70ab ???
0x5654d047f0db ???
0x5654d03b6cd0 ???
0x5654d03b70ef ???
0x5654d047f0db ???
0x5654d036ed08 ???
0x7f96c5548418 ???
0x7f96c54f9c9f ???
0x7f96c54f4b83 ???
0x7f96c5529420 ???
0x7f96c54e4b33 ???
0x5654d03632a6 ???
0x5654d022a526 ???
0x5654d047f164 ???
0x5654d03b6cd0 ???
0x5654d03b70ef ???
0x5654d047f0db ???
0x5654d03b6cd0 ???
0x5654d03b70ef ???
0x5654d047f0db ???
0x5654d036ed08 ???
0x7f96c5548418 ???
0x7f96c54f9c9f ???
0x7f96c54f4b83 ???
0x7f96c5500bb8 ???
0x7f96c54efd75 ???
0x7f96c5500bb8 ???
0x7f96c54efd75 ???
0x7f96c5500bb8 ???
0x7f96c54f48de ???
0x7f96c5500bb8 ???
0x7f96c54f48de ???
0x7f96c5500bb8 ???
0x7f96c54f01a9 ???
0x7f96c550be45 ???
0x7f96c54f0eb5 ???
0x7f96c54ee9bf ???
0x7f96c550bf6c ???
0x7f96c5500357 ???
0x7f96c559dcc0 ???
0x5654d05b11ba ???
0x5654d03617f2 ???
0x5654d02bc432 ???
0x5654d02b3f52 ???
0x5654d0535955 ???
0x5654d0535d06 ???
0x5654d02f3d24 ???
0x5654d009fc04 ???
0x7f96c4c3a28f ???
0x7f96c4c3a349 ???
0x5654d00a61e4 ???
0xffffffffffffffff ???
---------------------
../../gdb/gdbtypes.h:1064: internal-error: field: Assertion `idx >= 0 && idx <
num_fields ()' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) 

```

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|gdb                         |rust
                 CC|                            |tromey at sourceware dot org

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
This works for me.  I tried the gdb 12 release branch and also git master.

Can you try reproducing with '-nx' -- that is, avoid your add-ons?

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[amab8901 at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #2 from amir <amab8901 at protonmail dot com> ---
(In reply to Tom Tromey from comment #1)
> This works for me.  I tried the gdb 12 release branch and also git master.
> 
> Can you try reproducing with '-nx' -- that is, avoid your add-ons?

Oh, it works for me now that I used `-nx`. Thanks

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
This doesn't mean there isn't a gdb bug.
Maybe gdb-dashboard is running other commands behind the scenes.
It would be good to find out.

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[amab8901 at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #4 from amir <amab8901 at protonmail dot com> ---
(In reply to Tom Tromey from comment #3)
> This doesn't mean there isn't a gdb bug.
> Maybe gdb-dashboard is running other commands behind the scenes.
> It would be good to find out.

Any suggestions on specific steps I may try out?

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to amir from comment #4)

> Any suggestions on specific steps I may try out?

I don't know much about gdb-dashboard, so I don't know what to suggest.
Based on the assertion, I'd say maybe try "info local" at the
second breakpoint.  Otherwise maybe see if gdb-dashboard has some
kind of verbose mode or the like.

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-03-08
             Status|UNCONFIRMED                 |WAITING

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
Any new info on this?

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

The Puzzlemaker <tpzker at thepuzzlemaker dot info> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tpzker at thepuzzlemaker dot info

--- Comment #7 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
Created attachment 15198
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15198&action=edit
Patch for this issue, or an issue similar to it

I experienced this in 13.2. I believe it's related to the null pointer
optimization, or at least the case I encountered was.

```
use std::num::NonZeroUsize;
use std::hint::black_box;

pub fn main() {
    foo(black_box(NonZeroUsize::new(5)), black_box(NonZeroUsize::new(5)))
}

#[inline(never)]
pub fn foo(x: Option<NonZeroUsize>, y: Option<NonZeroUsize>) {
    black_box(x.unwrap().checked_add(y.unwrap().into()));
}
```

Put this in `tmp.rs`.
Compile with `rustc tmp.rs -Copt-level=1 -Cdebuginfo=full`
Run `gdb tmp::foo`
`break foo`
`run`
`info args`

Observe assertion fail:
```
x = core::option::Option<core::num::nonzero::NonZeroUsize>::Some(
../../gdb/gdbtypes.h:985: internal-error: field: Assertion `idx >= 0 && idx <
num_fields ()' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
```

This issue is related to this portion of code in `rust_lang::print_enum`:
```
 461   type = resolve_dynamic_type (type, view, value_address (val));
 ...   [snip]
 472   int variant_fieldno = rust_enum_variant (type);
 473   val = value_field (val, variant_fieldno);
 474   struct type *variant_type = type->field (variant_fieldno).type ();
```
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/rust-lang.c;h=74808ad0716e4d67f6af859f05ebff2b55d5e276;hb=662243de0e14a4945555a480dca33c0e677976eb#l461
The type from `resolve_dynamic_type` makes only the variant field of the active
discriminant in active. However, the type of `val` has *all* variant fields
enabled, thus making this index meaningless for that. I created a patch for
this, which is somewhat hacky--any maintainers here, feel free to change it up
a bit; I am a Rust developer by nature and don't know much about idiomatic C/++
and in general, what the GDB codebase looks like.

Please let me know if you'd like me to test/update this patch to the v14
codebase.

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #8 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
Woops, I apologize, I accidentally left a debugging `printf` in there. Give me
a moment and I'll upload the real patch

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #9 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
Comment on attachment 15198
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15198
Patch for this issue, or an issue similar to it

>From 07bb370168aab780c4780435ad3d9257ad8a474b Mon Sep 17 00:00:00 2001
>From: ThePuzzlemaker <tpzker@thepuzzlemaker.info>
>Date: Sat, 28 Oct 2023 13:28:33 -0500
>Subject: [PATCH] Fix assertion fail from `rust_lang::print_enum`
>
>This commit fixes an assertion fail in `rust_lang::print_enum` related
>to the handling of field numbers for variant types.
>---
> gdb/rust-lang.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
>diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
>index 74808ad0716..9acd2e1d2fa 100644
>--- a/gdb/rust-lang.c
>+++ b/gdb/rust-lang.c
>@@ -470,8 +470,18 @@ rust_language::print_enum (struct value *val, struct ui_file *stream,
>     }
> 
>   int variant_fieldno = rust_enum_variant (type);
>-  val = value_field (val, variant_fieldno);
>   struct type *variant_type = type->field (variant_fieldno).type ();
>+  /* HACK: variant_fieldno is indexed in 'type', which has the field
>+     disabled for other variants. The type of 'val' does not. Thus,
>+     iterate through the fields and find the one that matches. */
>+  for (int i = 0; i < value_type (val)->num_fields (); i++) {
>+    value* new_val = value_field (val, i);
>+    if (types_equal (value_type (new_val), variant_type)) {
>+      val = new_val;
>+      break;
>+    }
>+  }
>+  gdb_assert(types_equal(value_type (val), variant_type));
> 
>   int nfields = variant_type->num_fields ();
> 
>-- 
>2.42.0

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #10 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to The Puzzlemaker from comment #9)
> Comment on attachment 15198 [details]
> Patch for this issue, or an issue similar to it
> 
> >From 07bb370168aab780c4780435ad3d9257ad8a474b Mon Sep 17 00:00:00 2001
> >From: ThePuzzlemaker <tpzker@thepuzzlemaker.info>
> >Date: Sat, 28 Oct 2023 13:28:33 -0500
> >Subject: [PATCH] Fix assertion fail from `rust_lang::print_enum`
> >
> >This commit fixes an assertion fail in `rust_lang::print_enum` related
> >to the handling of field numbers for variant types.
> >---
> > gdb/rust-lang.c | 12 +++++++++++-
> > 1 file changed, 11 insertions(+), 1 deletion(-)
> >
> >diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
> >index 74808ad0716..9acd2e1d2fa 100644
> >--- a/gdb/rust-lang.c
> >+++ b/gdb/rust-lang.c
> >@@ -470,8 +470,18 @@ rust_language::print_enum (struct value *val, struct ui_file *stream,
> >     }
> > 
> >   int variant_fieldno = rust_enum_variant (type);
> >-  val = value_field (val, variant_fieldno);

This code looks different on trunk.
IIRC I fixed a bug like this a while ago.
git says 2020 though, which seems wrong if you're using 13.

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #11 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to The Puzzlemaker from comment #7)

> `break foo`
> `run`
> `info args`

This works for me with my 14.x build from git:

(gdb) info args
x =
core::option::Option<core::num::nonzero::NonZeroUsize>::Some(core::num::nonzero::NonZeroUsize
(
    5
  ))
y =
core::option::Option<core::num::nonzero::NonZeroUsize>::Some(core::num::nonzero::NonZeroUsize
(
    5
  ))

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #12 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
This is in fact fixed in 14.x git.

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #13 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
It seems it was 2023 actually.
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;f=gdb/rust-lang.c;h=debd0556e519c3d258299cf5f14a44cc01c795da

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

--- Comment #14 from The Puzzlemaker <tpzker at thepuzzlemaker dot info> ---
Thanks for your help. @amir, it'd be great if you could test and see if this
issue still occurs with GDB 14.x

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[sam at gentoo dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at gentoo dot org

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[Bug rust/29735] Can't have multiple breakpoints - crash otherwise

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29735

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|WAITING                     |RESOLVED
   Target Milestone|---                         |14.1

--- Comment #15 from Tom Tromey <tromey at sourceware dot org> ---
I think this is fixed.

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