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Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)
- From: Florian Weimer <fweimer at redhat dot com>
- To: Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>
- Cc: carlos <carlos at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, libc-alpha <libc-alpha at sourceware dot org>, Thomas Gleixner <tglx at linutronix dot de>, Ben Maurer <bmaurer at fb dot com>, Peter Zijlstra <peterz at infradead dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>, Boqun Feng <boqun dot feng at gmail dot com>, Will Deacon <will dot deacon at arm dot com>, Dave Watson <davejwatson at fb dot com>, Paul Turner <pjt at google dot com>, Rich Felker <dalias at libc dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, linux-api <linux-api at vger dot kernel dot org>
- Date: Mon, 14 Jan 2019 20:37:01 +0100
- Subject: Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)
- References: <20181204192141.4684-1-mathieu.desnoyers@efficios.com> <87h8fkz6qx.fsf@oldenburg2.str.redhat.com> <1681283664.1380.1547152315426.JavaMail.zimbra@efficios.com> <87fttv9iic.fsf@oldenburg2.str.redhat.com> <394676913.486.1547493757710.JavaMail.zimbra@efficios.com>
* Mathieu Desnoyers:
> ----- On Jan 14, 2019, at 10:55 AM, Florian Weimer fweimer@redhat.com wrote:
>
>> * Mathieu Desnoyers:
>>
>>> Therefore, both symbols will end up in
>>> sysdeps/unix/sysv/linux/Versions.
>>
>> I'm not sure what you mean by that. The physical location in the
>> directory tree has little effect on which shared object the symbol is
>> placed in; that will need other changes.
>
> I'm currently moving the symbol definitions to csu/rseq-sym.c. On Linux,
> its content is overridden by a new sysdeps/unix/sysv/linux/rseq-sym.c
> which contains both __rseq_abi and __rseq_refcount symbols. On other
> platforms, it is a stub file.
You don't need a stub file if you use the “ifeq ($(subdir),csu)”
construct.
The other question is whether this belongs into the csu subdirectory.
Since TLS is not available in ld.so, the initialization would have to
happen rather late, after relocation, but before ELF constructors are
run.
(A side effect is that the rseq area would not be usable from IFUNC
resolvers.)
Thanks,
Florian