From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Rich Felker <dalias@libc.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>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>,
Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>
Subject: Re: [RFC PATCH v4 1/5] glibc: Perform rseq(2) registration at nptl init and thread creation
Date: Mon, 26 Nov 2018 10:51:09 -0500 (EST) [thread overview]
Message-ID: <688718071.12798.1543247469553.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <87bm6cqm31.fsf@oldenburg.str.redhat.com>
----- On Nov 26, 2018, at 3:28 AM, Florian Weimer fweimer@redhat.com wrote:
> * Mathieu Desnoyers:
>
>> Using a "weak" symbol in early adopter libraries is important, so they
>> can be loaded together into the same process without causing loader
>> errors due to many definitions of the same strong symbol.
>
> This is not how ELF dynamic linking works. If the symbol name is the
> same, one definition interposes the others.
>
> You need to ensure that the symbol has the same size everywhere, though.
> There are some tricky interactions with symbol versions, too. (The
> interposing libraries must not use symbol versioning.)
I was under the impression that loading the same strong symbol into an
application multiple times would cause some kind of warning if non-weak. I did
some testing to figure out which case I remembered would cause this.
When compiling with "-fno-common", dynamic and static linking work fine, but
trying to add multiple instances of a given symbol into a single object fails
with:
/tmp/ccSakXZV.o:(.bss+0x0): multiple definition of `a'
/tmp/ccQBJBOo.o:(.bss+0x0): first defined here
Even if the symbol has the same size.
So considering that we don't care about compiling into a single object here,
and only care about static and dynamic linking of libraries, indeed the "weak"
symbol is not useful.
So let's make __rseq_abi and __rseq_refcount strong symbols then ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2018-11-26 15:51 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-21 18:39 [RFC PATCH v4 1/5] glibc: Perform rseq(2) registration at nptl init and thread creation Mathieu Desnoyers
2018-11-21 18:39 ` [RFC PATCH v4 2/5] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux Mathieu Desnoyers
2018-11-22 14:36 ` [RFC PATCH v4 1/5] glibc: Perform rseq(2) registration at nptl init and thread creation Rich Felker
2018-11-22 15:04 ` Mathieu Desnoyers
2018-11-22 15:11 ` Florian Weimer
2018-11-22 15:17 ` Rich Felker
2018-11-22 15:21 ` Florian Weimer
2018-11-22 15:33 ` Mathieu Desnoyers
2018-11-22 15:44 ` Rich Felker
2018-11-22 16:24 ` Szabolcs Nagy
2018-11-22 18:35 ` Mathieu Desnoyers
2018-11-22 19:01 ` Rich Felker
2018-11-22 19:36 ` Mathieu Desnoyers
2018-11-22 15:14 ` Rich Felker
2018-11-22 15:47 ` Mathieu Desnoyers
2018-11-22 16:28 ` Florian Weimer
2018-11-22 16:47 ` Mathieu Desnoyers
2018-11-22 16:59 ` Florian Weimer
2018-11-22 17:10 ` Rich Felker
2018-11-23 13:10 ` Florian Weimer
2018-11-23 14:28 ` Rich Felker
2018-11-23 17:05 ` Mathieu Desnoyers
2018-11-23 17:30 ` Rich Felker
2018-11-23 17:39 ` Florian Weimer
2018-11-23 17:44 ` Rich Felker
2018-11-23 18:01 ` Florian Weimer
2018-11-23 17:52 ` Mathieu Desnoyers
2018-11-23 18:35 ` Rich Felker
2018-11-23 21:09 ` Mathieu Desnoyers
2018-11-26 8:28 ` Florian Weimer
2018-11-26 15:51 ` Mathieu Desnoyers [this message]
2018-11-26 16:03 ` Florian Weimer
2018-11-26 17:10 ` Rich Felker
2018-11-26 19:22 ` Mathieu Desnoyers
2018-12-03 21:30 ` Mathieu Desnoyers
2018-11-26 16:30 ` Mathieu Desnoyers
2018-11-26 17:07 ` Rich Felker
2018-12-05 17:24 ` Mathieu Desnoyers
2018-11-26 11:56 ` Szabolcs Nagy
2018-11-22 17:29 ` Mathieu Desnoyers
2018-11-23 13:29 ` Florian Weimer
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