linux-kernel - Re: [RFC PATCH glibc 1/3] glibc: Perform rseq(2) registration at C startup and thread creation (v18)

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Message-ID: <874kt0lx6i.fsf@oldenburg2.str.redhat.com>
Date:   Thu, 30 Apr 2020 19:07:17 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     carlos <carlos@...hat.com>, Joseph Myers <joseph@...esourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        libc-alpha <libc-alpha@...rceware.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ben Maurer <bmaurer@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Rich Felker <dalias@...c.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [RFC PATCH glibc 1/3] glibc: Perform rseq(2) registration at C startup and thread creation (v18)

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

__libc_fatal does not attribute the error to glibc, so I suggest to
start the error messages with “glibc fatal error: ”, so that people know
where to look.

Thanks,
Florian