[Bug 2041396] Re: gdb 12.1 generates SIGILL on armhf

[Zixing Liu]

** Description changed:

- GDB 12.1 had a regression where it will break program execution when the
- program contains mixed ARM code and THUMB code.
+ [ Impact ]
+ 
+  * GDB 12.1 introduced a regression where it will break program execution when the program contains mixed ARM code and THUMB code.
+  * Upstream stated they tested the changes on Ubuntu 20.04 and it went okay.
+ 
+ [ Test Plan ]
  
  Considering the following C program:
  
  ```
  __attribute__((target("arm"), noinline))
  int thumb_func() {
-   return 42;
+   return 42;
  }
  
  __attribute__((target("thumb")))
  int main() { return thumb_func(); }
  ```
  
  If you build it using `gcc repro.c -ggdb3 -Og -o repro` and run the GDB
- using the following commands:
+ using the following commands ...
  
  ```
  b 3
  r
  c
  ```
  
- (you can save it to a file and run GDB using `gdb -x script ./repro`)
+ (you can save the contents above to a file and run GDB using `gdb -x
+ script ./repro`)
  
- You will notice GDB broke the program and threw SIGILL.
+ ... you will notice GDB broke the program and threw SIGILL.
  If you run the program without GDB, the program exits normally.
  
- This bug has been fixed in GDB 13, but the fix was never backported to
- GDB 12. You can find the upstream bug in the remote bug watch.
+ [ Where problems could occur ]
+ 
+  * GDB is a complex software. As the patch suggests, it may break other use cases (like single-stepping) entirely.
+  * Since this is an ARM-only patch, it's unlikely to affect other CPU architectures. However, it is possible that this fix may break ARM64 execution.
+ 
+ [ Other Info ]
+  
+  * This bug has been fixed in GDB 13, but the fix was never backported to GDB 12. You can find the upstream bug in the remote bug watch.

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https://bugs.launchpad.net/bugs/2041396

Title:
  gdb 12.1 generates SIGILL on armhf

Status in gdb:
  Unknown
Status in gdb package in Ubuntu:
  New

Bug description:
  [ Impact ]

   * GDB 12.1 introduced a regression where it will break program execution when the program contains mixed ARM code and THUMB code.
   * Upstream stated they tested the changes on Ubuntu 20.04 and it went okay.

  [ Test Plan ]

  Considering the following C program:

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

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

  If you build it using `gcc repro.c -ggdb3 -Og -o repro` and run the
  GDB using the following commands ...

  ```
  b 3
  r
  c
  ```

  (you can save the contents above to a file and run GDB using `gdb -x
  script ./repro`)

  ... you will notice GDB broke the program and threw SIGILL.
  If you run the program without GDB, the program exits normally.

  [ Where problems could occur ]

   * GDB is a complex software. As the patch suggests, it may break other use cases (like single-stepping) entirely.
   * Since this is an ARM-only patch, it's unlikely to affect other CPU architectures. However, it is possible that this fix may break ARM64 execution.

  [ Other Info ]
   
   * This bug has been fixed in GDB 13, but the fix was never backported to GDB 12. You can find the upstream bug in the remote bug watch.

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