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From: Florian Weimer <fweimer@redhat.com>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
	 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	 "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>,
	 "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>,
	 Joseph Myers <joseph@codesourcery.com>
Subject: Re: [RFC] <sys/tagged-address.h>: An API for tagged address
Date: Thu, 18 Feb 2021 14:28:47 +0100	[thread overview]
Message-ID: <874ki9mrn4.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20210218132419.GD12795@arm.com> (Szabolcs Nagy's message of "Thu, 18 Feb 2021 13:24:19 +0000")

* Szabolcs Nagy:

>> was called in a thread.  It won't work when 2 threads have different address
>> masks.  I think set_tagged_address_mask should be disallowed in child
>> threads and in parent thread when there are any active child threads.
>
> i think this is the wrong api. currently the libc should set
> things up early. api for user code is too late.
>
> user code does not know if it runs single threaded or not
> (although we have __libc_single_threaded now, i'm not sure if
> we can use that for this purpose)

We could, but it's possible to launch threads from ELF constructors (and
I think some libraries do that).  So you could avoid the call or
diagnose a failure if single-threaded, but the tagged address feature
wouldn't compose well.

Some kernel interfaces have this problem (e.g., unshare), but they are
less general-purpose than tagged addresses.

Thanks,
Florian


  reply	other threads:[~2021-02-18 13:28 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-11 17:37 H.J. Lu
2021-02-11 20:28 ` Joseph Myers
2021-02-11 21:39   ` H.J. Lu
2021-02-12  9:43     ` Florian Weimer
2021-02-12 13:06       ` H.J. Lu
2021-02-17 18:43         ` H.J. Lu
2021-02-17 21:58           ` H.J. Lu
2021-02-18 13:24             ` Szabolcs Nagy
2021-02-18 13:28               ` Florian Weimer [this message]
2021-02-18 13:50                 ` Szabolcs Nagy
2021-02-18 22:32                   ` H.J. Lu
2021-02-22  8:27                     ` Szabolcs Nagy
2021-02-22 13:57                       ` H.J. Lu
2021-02-18 13:17         ` Szabolcs Nagy
2021-02-18 13:21           ` Florian Weimer

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