linux-kernel - Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)

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Message-ID: <1031872348.636.1547497648914.JavaMail.zimbra@efficios.com>
Date:   Mon, 14 Jan 2019 15:27:28 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fweimer@...hat.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 E. McKenney" <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 1/4] glibc: Perform rseq(2) registration at
 nptl init and thread creation (v4)

----- On Jan 14, 2019, at 2:37 PM, Florian Weimer fweimer@...hat.com wrote:

> * Mathieu Desnoyers:
> 
>> ----- On Jan 14, 2019, at 10:55 AM, Florian Weimer fweimer@...hat.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.

OK

> 
> 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.)

Do you have a specific directory location in mind where we should put
the built object ? e.g. "ifeq ($(subdir),posix)" or
"ifeq ($(subdir),misc)" ?

Moreover, from where should we call the rseq initialization ? I'm having
trouble with invalid system calls parameters if I place it in
LIBC_START_MAIN() just before or after the call to __pthread_initialize_minimal.
I get what appears to be invalid parameters to sys_rseq, possibly due to
stack corruption (?). I'm investigating at the moment. But if you prefer
we call the rseq init from elsewhere, please let me know.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com