Re: [PATCH] [gdb/testsuite] Extend gdb.base/kill-during-detach.exp

[Kevin Buettner <kevinb@redhat.com>]

On Tue,  9 Jan 2024 17:56:20 +0100
Tom de Vries <tdevries@suse.de> wrote:

> I ran into the following FAIL:
> ...
> (gdb) python kill_and_detach()^M
> Traceback (most recent call last):^M
>   File "<string>", line 1, in <module>^M
>   File "<string>", line 7, in kill_and_detach^M
> gdb.error: Selected thread is running.^M
> Error while executing Python code.^M
> (gdb) FAIL: gdb.base/kill-during-detach.exp: exit_p=true: checkpoint_p=true: \
>   python kill_and_detach()
> ...
> 
> The FAIL happens as follows:
> - gdb is debugging a process A
> - a checkpoint is created, in other words, fork is called in the inferior,
>   after which we have:
>   - checkpoint 0 (the fork parent, process A), and
>   - checkpoint 1 (the fork child, process B).
> - during checkpoint creation, lseek is called in the inferior (process A) for
>   all file descriptors, and it returns != -1 for at least one file descriptor.
> - the process A continues in the background
> - gdb detaches, from process A
> - gdb switches to process B, in other words, it restarts checkpoint 1
> - while restarting checkpoint 1, gdb tries to call lseek in the inferior
>   (process B), but this fails because gdb incorrectly thinks that inferior B
>   is running.
> 
> This happens because linux_nat_switch_fork patches the pid of process B into
> the current inferior and current thread which where originally representing
> process A.  So, because process A was running in the background, the
> thread_info fields executing and resumed are set accordingly, but they are not
> correct for process B.
> 
> There's a line in fork_load_infrun_state that fixes up the thread_info field
> stop_pc, so fix this by adding similar fixups for the executing and resumed
> fields alongside.
> 
> The FAIL did not always reproduce, so extend the test-case to reliably
> trigger this scenario.

Thanks for the detailed explanation!

Makes sense to me...

Approved-By: Kevin Buettner <kevinb@redhat.com>