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From: Florian Weimer <fweimer@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH 2/5] nptl: Add rseq registration
Date: Mon, 06 Dec 2021 18:14:58 +0100	[thread overview]
Message-ID: <871r2podt9.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <1780152866.15126.1638809966443.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Mon, 6 Dec 2021 11:59:26 -0500 (EST)")

* Mathieu Desnoyers:

> ----- On Dec 6, 2021, at 8:46 AM, Florian Weimer fweimer@redhat.com wrote:
> [...]
>> @@ -406,6 +407,9 @@ struct pthread
>>   /* Used on strsignal.  */
>>   struct tls_internal_t tls_state;
>> 
>> +  /* rseq area registered with the kernel.  */
>> +  struct rseq rseq_area;
>
> The rseq UAPI requires that the fields within the rseq_area
> are read-written with single-copy atomicity semantics.
>
> So either we define a "volatile struct rseq" here, or we'll need
> to wrap all accesses with the proper volatile casts, or use the
> relaxed_mo atomic accesses.

Under the C memory model, neither volatile nor relaxed MO result in
single-copy atomicity semantics.  So I'm not sure what to make of this.
Surely switching to inline assembly on all targets is over the top.

I think we can rely on a plain read doing the right thing for us.

Thanks,
Florian


  reply	other threads:[~2021-12-06 17:15 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-06 13:45 [PATCH 0/5] Extensible rseq support for glibc Florian Weimer
2021-12-06 13:46 ` [PATCH 1/5] nptl: Add <thread_pointer.h> for defining __thread_pointer Florian Weimer
2021-12-06 16:44   ` Mathieu Desnoyers
2021-12-06 17:01     ` Florian Weimer
2021-12-06 19:55       ` Florian Weimer
2021-12-06 13:46 ` [PATCH 2/5] nptl: Add rseq registration Florian Weimer
2021-12-06 16:53   ` Mathieu Desnoyers
2021-12-06 17:10     ` Florian Weimer
2021-12-06 16:59   ` Mathieu Desnoyers
2021-12-06 17:14     ` Florian Weimer [this message]
2021-12-06 18:52       ` Mathieu Desnoyers
2021-12-06 19:03         ` Florian Weimer
2021-12-06 20:11           ` Paul E. McKenney
2021-12-06 20:26             ` Florian Weimer
2021-12-06 21:08               ` Paul E. McKenney
2021-12-06 13:46 ` [PATCH 3/5] Linux: Use rseq to accelerate sched_getcpu Florian Weimer
2021-12-06 16:50   ` Szabolcs Nagy
2021-12-06 17:06     ` Florian Weimer
2021-12-06 17:45       ` Szabolcs Nagy
2021-12-07 15:48         ` Florian Weimer
2021-12-06 13:46 ` [PATCH 4/5] nptl: Add glibc.pthread.rseq tunable to control rseq registration Florian Weimer
2021-12-06 13:53 ` [PATCH 5/5] nptl: Add public rseq symbols and <sys/rseq.h> Florian Weimer
2021-12-07 11:01   ` Szabolcs Nagy
2021-12-07 11:28     ` Florian Weimer
2021-12-06 16:13 ` [PATCH 0/5] Extensible rseq support for glibc Mathieu Desnoyers

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