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From:   Florian Weimer <fweimer@redhat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     carlos <carlos@redhat.com>, Joseph Myers <joseph@codesourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        libc-alpha <libc-alpha@sourceware.org>,
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        Peter Zijlstra <peterz@infradead.org>,
        Paul <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Will Deacon <will.deacon@arm.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: [RFC PATCH glibc 1/3] glibc: Perform rseq(2) registration at C startup and thread creation (v18)
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Date:   Thu, 30 Apr 2020 19:07:17 +0200
In-Reply-To: <1972833271.77975.1588265754974.JavaMail.zimbra@efficios.com>
        (Mathieu Desnoyers's message of "Thu, 30 Apr 2020 12:55:54 -0400
        (EDT)")
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* Mathieu Desnoyers:

> If we go this way, I'd also recommend to treat any situation where
> __rseq_abi.cpu_id is already initialized as a fatal error. Does the
> code below seem OK to you ?
>
> static inline void
> rseq_register_current_thread (void)
> {
>   int ret;
>
>   if (__rseq_abi.cpu_id !=3D RSEQ_CPU_ID_UNINITIALIZED)
>     __libc_fatal ("rseq already initialized for this thread\n");

Agreed; this should work because this code runs after relocation
processing.

>   ret =3D INTERNAL_SYSCALL_CALL (rseq, &__rseq_abi, sizeof (struct rseq),
>                               0, RSEQ_SIG);
>   if (INTERNAL_SYSCALL_ERROR_P (ret))
>     {
>       if (INTERNAL_SYSCALL_ERRNO (ret) =3D=3D EBUSY)
>         __libc_fatal ("rseq already registered for this thread\n");
>       __rseq_abi.cpu_id =3D RSEQ_CPU_ID_REGISTRATION_FAILED;
>     }
> }

__libc_fatal does not attribute the error to glibc, so I suggest to
start the error messages with =E2=80=9Cglibc fatal error: =E2=80=9D, so tha=
t people know
where to look.

Thanks,
Florian