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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 1 Apr 2021 09:24:57 -0700
Message-ID: <CAHk-=wh-VE=4puZ+r-Mo0GcAUou3aKrvnNsU3JxjnMXNcJOoug@mail.gmail.com>
Subject: Re: [PATCH 0/6] Allow signals for IO threads
To:     Stefan Metzmacher <metze@samba.org>
Cc:     Jens Axboe <axboe@kernel.dk>, io-uring <io-uring@vger.kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Apr 1, 2021 at 9:00 AM Stefan Metzmacher <metze@samba.org> wrote:
>
> I haven't tried it, but it seems gdb tries to use PTRACE_PEEKUSR
> against the last thread tid listed under /proc/<pid>/tasks/ in order to
> get the architecture for the userspace application

Christ, what an odd hack. Why wouldn't it just do it on the initial
thread you actually attached to?

Are you sure it's not simply because your test-case was to attach to
the io_uring thread? Because the io_uring thread might as well be
considered to be 64-bit.

> so my naive assumption
> would be that it wouldn't allow the detection of a 32-bit application
> using a 64-bit kernel.

I'm not entirely convinced we want to care about a confused gdb
implementation and somebody debugging a case that I don't believe
happens in practice.

32-bit user space is legacy. And legacy isn't io_uring. If somebody
insists on doing odd things, they can live with the odd results.

                  Linus