gdb 12.1 generates SIGILL on armhf

I have proposed a fix in https://code.launchpad.net/~liushuyu-011/ubuntu/+source/gdb/+git/gdb/+merge/454654.

After several hours trying to obtain access to an ARM64 machine where I could test the fix, vorlon kindly provided me with credentials to a machine that's capable of launching an armhf container.

I could reproduce the bug:

# gdb -q ./a.out -ex 'b 3' -ex r -ex c
Reading symbols from ./a.out...
Breakpoint 1, thumb_func () at 1.c:3
3 return 42;
Continuing.

Program received signal SIGILL, Illegal instruction.
0x00401004 in ?? ()
...

And also verify that Liu's package fixes the problem:

# gdb -q ./a.out -ex 'b 3' -ex r -ex c
Reading symbols from ./a.out...
Breakpoint 1 at 0x4d8: file 1.c, line 3.
Starting program: /root/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Breakpoint 1, thumb_func () at 1.c:3
3 return 42;
Continuing.
[Inferior 1 (process 2666) exited with code 052]

Therefore, I sponsored the upload for him.

Currently waiting for an SRU team member to process the update through the upload queue.

Hello Zixing, or anyone else affected,

Accepted gdb into jammy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gdb/12.1-0ubuntu1~22.04.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-jammy to verification-done-jammy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-jammy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

All autopkgtests for the newly accepted gdb (12.1-0ubuntu1~22.04.1) for jammy have finished running.
The following regressions have been reported in tests triggered by the package:

linux-aws-5.19/5.19.0-1029.30~22.04.1 (arm64)
linux-aws-6.2/6.2.0-1015.15~22.04.1 (arm64)
linux-azure-5.19/5.19.0-1027.30~22.04.2 (arm64)
linux-azure-6.2/6.2.0-1016.16~22.04.1 (arm64)
linux-azure-6.5/6.5.0-1007.7~22.04.1 (arm64)
linux-gcp-5.19/5.19.0-1030.32~22.04.1 (arm64)
linux-gcp-6.2/6.2.0-1018.20~22.04.1 (arm64)
linux-gke/5.15.0-1046.51 (arm64)
linux-hwe-5.19/5.19.0-50.50 (arm64)
linux-hwe-6.2/6.2.0-39.40~22.04.1 (arm64)
linux-lowlatency/5.15.0-91.101 (arm64)
linux-lowlatency-hwe-5.19/5.19.0-1030.30 (arm64)
linux-lowlatency-hwe-6.2/6.2.0-1018.18~22.04.1 (arm64)
linux-nvidia-tegra/5.15.0-1019.19 (arm64)
linux-oracle-5.19/5.19.0-1027.30 (arm64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/jammy/update_excuses.html#gdb

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

Verification Report
===================

The test is conducted on an RK3399 device (with 4x ARM Cortex-A53 cores + 2x ARM Cortex-A72 cores).

Test (1) original Rust program test (associated-types.rs)
---------------------------------------------------------

GDB 12.1-0ubuntu1~22.04 (unpatched)
Rust 1.70.0+dfsg0ubuntu1~bpo2-0ubuntu0.22.04.2

Test program source: https://github.com/rust-lang/rust/blob/1.68.2/tests/debuginfo/associated-types.rs

GDB script content:
```
b associated-types.rs:111
r
c
```

Result:

```
Breakpoint 1 at 0x4838: file associated-types.rs, line 111.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Breakpoint 1, associated_types::assoc_struct<i32> (arg=...) at associated-types.rs:111
111 zzz(); // #break

Program received signal SIGILL, Illegal instruction.
0x00404ec4 in core::slice::cmp::{impl#5}::equal<u8, u8> (self=..., other=...) at library/core/src/slice/cmp.rs:91
91 library/core/src/slice/cmp.rs: No such file or directory.
```

>>> SRU'ed package:

GDB 12.1-0ubuntu1~22.04.1 (patched)
GCC 11.4.0-1ubuntu1~22.04

Result:
```
Breakpoint 1 at 0x4838: file associated-types.rs, line 111.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Breakpoint 1, associated_types::assoc_struct<i32> (arg=...) at associated-types.rs:111
111 zzz(); // #break
[Inferior 1 (process 3621) exited normally]
```

Test (2) simplified C program test (test.c)
-------------------------------------------

GDB 12.1-0ubuntu1~22.04 (unpatched)
GCC 11.4.0-1ubuntu1~22.04

Test program source:
```
__attribute__((target("arm"), noinline))
int thumb_func() {
  return 42;
}

__attribute__((target("thumb")))
int main() { return thumb_func(); }
```

Commands:
```
gcc -Og -ggdb3 test.c -o test
printf "b 3\nr\nc\n" > repro
gdb --batch -x ./repro ./test
```

Result:
```
Breakpoint 1 at 0x4d8: file test.c, line 3.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Breakpoint 1, thumb_func () at test.c:3
3 return 42;

Program received signal SIGILL, Illegal instruction.
0x00401004 in ?? ()
```

Disassembly of the crash site (ARM code):

```
=> 0x004004d8 <+0>: mov r0, #42 ; 0x2a
   0x004004dc <+4>: bx lr
```

Disassembly of the call site (Thumb code, +2 bytes):
```
   0x004004e0 <+0>: push {r3, lr}
   0x004004e2 <+2>: blx 0x4004d8 <thumb_func>
=> 0x004004e6 <+6>: pop {r3, pc}
```

>>> SRU'ed package:

GDB 12.1-0ubuntu1~22.04.1 (patched)
GCC 11.4.0-1ubuntu1~22.04

Result:
```
Breakpoint 1 at 0x4d8: file test.c, line 3.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Breakpoint 1, thumb_func () at test.c:3
3 return 42;
[Inferior 1 (process 3611) exited with code 052]
```

Conclusion
----------
GDB 12.1-0ubuntu1~22.04.1 package correctly fixed the issue described in the bug report.

The where problems could occur section says "it is possible that this fix may break ARM64 execution". How was it verified that this is not broken?

> The where problems could occur section says "it is possible that this fix may break ARM64 execution". How was it verified that this is not broken?

I believe this could be verified by running the GDB tests inside the Rust testing suite.
Should I queue an autopkgtest against rustc for GDB in this case?

Given the current size of the queues that might take some time. Could you run the test locally on the same device which you verified the fix on?