From: Carlos O'Donell <codonell@redhat.com>
To: Florian Weimer <fweimer@redhat.com>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Paul Burton <paul.burton@mips.com>,
Will Deacon <will.deacon@arm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Russell King <linux@armlinux.org.uk>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, carlos <carlos@redhat.com>,
Joseph Myers <joseph@codesourcery.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha <libc-alpha@sourceware.org>,
Thomas Gleixner <tglx@linutronix.de>, Ben Maurer <bmaurer@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
Rich Felker <dalias@libc.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>
Subject: Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)
Date: Thu, 4 Apr 2019 16:32:53 -0400 [thread overview]
Message-ID: <ce6f9db3-bf85-7aec-4bae-998e6fd629e1@redhat.com> (raw)
In-Reply-To: <87pnq4zxyj.fsf@oldenburg2.str.redhat.com>
On 4/2/19 3:08 AM, Florian Weimer wrote:
> * Michael Ellerman:
>
>> I'm a bit vague on what we're trying to do here.
>>
>> But it seems like you want some sort of "eye catcher" prior to the branch?
>>
>> That value is a valid instruction on current CPUs (rlwimi.
>> r5,r24,6,1,9), and even if it wasn't it could become one in future.
>>
>> If you change it to 0x8053530 that is both a valid instruction and is a
>> nop (conditional trap immediate but with no conditions set).
>
> I think we need something that is very unlikely to appear in the
> instruction stream. It's just a marker. The instruction will never be
> executed, and it does not have to be a trap, either (I believe that a
> standard trap instruction would be a bad choice).
I assume you want to avoid a standard trap instruction because it would
be common, and so not meet the intent of the RSEQ_SIG choice as being something
that is *uncommon* right?
It is valuable that it be a trap, particularly for constant pools because
it means that a jump into the constant pool will trap.
--
Cheers,
Carlos.
next prev parent reply other threads:[~2019-04-04 20:33 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190212194253.1951-1-mathieu.desnoyers@efficios.com>
2019-02-12 19:42 ` [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7) Mathieu Desnoyers
2019-03-22 20:09 ` Carlos O'Donell
2019-03-25 15:54 ` Mathieu Desnoyers
2019-03-27 9:16 ` Martin Schwidefsky
2019-03-27 20:01 ` Mathieu Desnoyers
2019-03-27 20:38 ` Carlos O'Donell
2019-03-28 7:49 ` Martin Schwidefsky
2019-03-28 15:42 ` Mathieu Desnoyers
2019-04-02 6:02 ` Michael Ellerman
2019-04-02 7:08 ` Florian Weimer
2019-04-04 20:32 ` Carlos O'Donell [this message]
2019-04-05 9:16 ` Florian Weimer
2019-04-05 15:40 ` Carlos O'Donell
2019-04-08 19:20 ` Tulio Magno Quites Machado Filho
2019-04-08 21:45 ` Carlos O'Donell
2019-04-09 4:23 ` Michael Ellerman
2019-04-09 9:29 ` Alan Modra
[not found] ` <871s2bp9f9.fsf@linux.ibm.com>
2019-04-09 14:13 ` Carlos O'Donell
2019-04-09 15:45 ` Mathieu Desnoyers
2019-04-18 15:31 ` Mathieu Desnoyers
2019-04-09 16:33 ` Mathieu Desnoyers
2019-04-04 20:15 ` Carlos O'Donell
2019-04-04 20:50 ` Carlos O'Donell
2019-04-04 21:41 ` Paul Burton
2019-04-09 16:40 ` Mathieu Desnoyers
2019-04-18 18:58 ` Mathieu Desnoyers
2019-04-24 15:05 ` Mathieu Desnoyers
2019-04-24 23:13 ` Paul Burton
2019-04-25 0:41 ` Maciej W. Rozycki
2019-02-12 19:42 ` [PATCH 2/4] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux Mathieu Desnoyers
2019-03-22 20:13 ` Carlos O'Donell
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