From: Florian Weimer <fweimer@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: libc-alpha <libc-alpha@sourceware.org>,
Rich Felker <dalias@libc.org>,
linux-api <linux-api@vger.kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ben Maurer <bmaurer@fb.com>, Dave Watson <davejwatson@fb.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paul <paulmck@linux.vnet.ibm.com>, Paul Turner <pjt@google.com>,
Joseph Myers <joseph@codesourcery.com>
Subject: Re: [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v19)
Date: Tue, 26 May 2020 16:57:56 +0200 [thread overview]
Message-ID: <877dwypwuj.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <1931644690.34207.1590504804638.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Tue, 26 May 2020 10:53:24 -0400 (EDT)")
* Mathieu Desnoyers:
>> Like the attribute, it needs to come right after the struct keyword, I
>> think. (Trailing attributes can be ambiguous, but not in this case.)
>
> Nope. _Alignas really _is_ special :-(
>
> struct _Alignas (16) blah {
> int a;
> };
>
> p.c:1:8: error: expected ‘{’ before ‘_Alignas’
> struct _Alignas (16) blah {
Meh, yet another unnecessary C++ incompatibility. C does not support
empty structs, so I assume they didn't see the field requirement as a
burden.
> One last thing I'm planning to add in sys/rseq.h to cover acessing the
> rseq_cs pointers with both the UAPI headers and the glibc struct rseq
> declarations:
>
> /* The rseq_cs_ptr macro can be used to access the pointer to the current
> rseq critical section descriptor. */
> #ifdef __LP64__
> # define rseq_cs_ptr(rseq) \
> ((const struct rseq_cs *) (rseq)->rseq_cs.ptr)
> #else /* __LP64__ */
> # define rseq_cs_ptr(rseq) \
> ((const struct rseq_cs *) (rseq)->rseq_cs.ptr.ptr32)
> #endif /* __LP64__ */
>
> Does it make sense ?
Written this way, it's an aliasing violation. I don't think it's very
useful.
Thanks,
Florian
next prev parent reply other threads:[~2020-05-26 14:58 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-01 2:14 [PATCH glibc 0/3] Restartable Sequences enablement Mathieu Desnoyers
2020-05-01 2:14 ` [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v19) Mathieu Desnoyers
2020-05-20 11:40 ` Florian Weimer
2020-05-25 14:51 ` Mathieu Desnoyers
2020-05-25 15:20 ` Florian Weimer
2020-05-25 17:36 ` Mathieu Desnoyers
2020-05-26 12:41 ` Florian Weimer
2020-05-26 14:32 ` Mathieu Desnoyers
2020-05-26 14:38 ` Florian Weimer
2020-05-26 14:53 ` Mathieu Desnoyers
2020-05-26 14:57 ` Florian Weimer [this message]
2020-05-26 15:22 ` Mathieu Desnoyers
2020-05-01 2:14 ` [PATCH glibc 2/3] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v7) Mathieu Desnoyers
2020-05-20 10:14 ` Florian Weimer
2020-05-01 2:14 ` [PATCH glibc 3/3] rseq registration tests (v10) Mathieu Desnoyers
2020-05-20 10:52 ` Florian Weimer
2020-05-25 17:07 ` Mathieu Desnoyers
2020-05-26 12:47 ` Florian Weimer
2020-05-26 14:43 ` Mathieu Desnoyers
2020-05-27 15:05 ` Mathieu Desnoyers
2020-05-27 15:12 ` Florian Weimer
2020-05-27 15:17 ` Mathieu Desnoyers
2020-05-27 15:21 ` Florian Weimer
2020-05-27 15:30 ` Mathieu Desnoyers
2020-05-20 11:44 ` [PATCH glibc 0/3] Restartable Sequences enablement Florian Weimer
2020-05-25 13:52 ` Mathieu Desnoyers
2020-05-25 14:28 ` Florian Weimer
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