From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: carlos <carlos@redhat.com>
Cc: Florian Weimer <fweimer@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>,
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 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v5)
Date: Mon, 21 Jan 2019 16:23:55 -0500 (EST) [thread overview]
Message-ID: <1189519139.464.1548105835783.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <1887968822.1146.1547833305059.JavaMail.zimbra@efficios.com>
----- On Jan 18, 2019, at 12:41 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
> ----- On Jan 14, 2019, at 8:51 PM, Mathieu Desnoyers
> mathieu.desnoyers@efficios.com wrote:
>
> [...]
>
>> diff --git a/sysdeps/unix/sysv/linux/rseq-sym.c
>> b/sysdeps/unix/sysv/linux/rseq-sym.c
>> new file mode 100644
>> index 0000000000..6856d0388a
> [...]
>> +/* volatile because fields can be read/updated by the kernel. */
>> +__thread volatile struct rseq __rseq_abi = {
>> + .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
>> +};
>> +
>> +/* volatile because refcount can be read/updated by signal handlers. */
>> +__thread volatile uint32_t __rseq_refcount;
>
> Back to the weak vs non-weak question about those two symbols. I understand
> that tagging them as weak symbols has little effect on the dynamic loader
> when it loads libc.so. However, I'm worried about that happens when
> libc is statically linked into an application, and there happens to
> be more than one instance of those symbols (e.g. libc and another library
> define the same symbols, and both are statically linked into the same
> application). Isn't it a situation where tagging those symbols as "weak"
> becomes useful ?
Testing shows that it seems fine to statically link two archives within an
executable in a scenario where each .a defines the same symbol, without
using "weak", so I won't worry about this further.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
prev parent reply other threads:[~2019-01-21 21:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 1:51 [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v5) Mathieu Desnoyers
2019-01-15 1:51 ` [RFC PATCH glibc 2/4] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux Mathieu Desnoyers
2019-01-15 1:51 ` [RFC PATCH glibc 3/4] support record failure: allow use from constructor Mathieu Desnoyers
2019-01-15 1:51 ` [RFC PATCH glibc 4/4] rseq registration tests (v2) Mathieu Desnoyers
2019-01-18 17:41 ` [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v5) Mathieu Desnoyers
2019-01-21 21:23 ` Mathieu Desnoyers [this message]
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