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Date:   Wed, 3 Jun 2020 08:22:43 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     Florian Weimer <fweimer@redhat.com>
Cc:     carlos <carlos@redhat.com>, Joseph Myers <joseph@codesourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        libc-alpha <libc-alpha@sourceware.org>,
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        Peter Zijlstra <peterz@infradead.org>,
        Paul <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>
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References: <20200527185130.5604-1-mathieu.desnoyers@efficios.com> <20200527185130.5604-2-mathieu.desnoyers@efficios.com> <87d06gxsla.fsf@oldenburg2.str.redhat.com>
Subject: Re: [PATCH glibc 1/3] glibc: Perform rseq registration at C startup
 and thread creation (v20)
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Thread-Topic: glibc: Perform rseq registration at C startup and thread creation (v20)
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----- On Jun 3, 2020, at 8:05 AM, Florian Weimer fweimer@redhat.com wrote:

> * Mathieu Desnoyers:
>=20
>> +#ifdef __cplusplus
>> +# if  __cplusplus >=3D 201103L
>> +#  define __rseq_static_assert(expr, diagnostic) static_assert (expr,
>> diagnostic)
>> +#  define __rseq_alignof(type)                   alignof (type)
>> +#  define __rseq_alignas(x)                      alignas (x)
>> +#  define __rseq_tls_storage_class               thread_local
>> +# endif
>> +#elif (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) >=3D 201112L
>> +# define __rseq_static_assert(expr, diagnostic)  _Static_assert (expr,
>> diagnostic)
>> +# define __rseq_alignof(type)                    _Alignof (type)
>> +# define __rseq_alignas(x)                       _Alignas (x)
>> +# define __rseq_tls_storage_class                _Thread_local
>> +#endif
>=20
> This does not seem to work.  I get this with GCC 9:
>=20
> In file included from /tmp/cih_test_gsrKbC.cc:8:0:
> ../sysdeps/unix/sysv/linux/sys/rseq.h:42:50: error: attribute ignored
> [-Werror=3Dattributes]
> #  define __rseq_alignas(x)                      alignas (x)
>                                                  ^
> ../sysdeps/unix/sysv/linux/sys/rseq.h:122:14: note: in expansion of macro
> =E2=80=98__rseq_alignas=E2=80=99
>     uint32_t __rseq_alignas (32) version;
>              ^

Is that when compiling C or C++ code ? If it's C code, I would expect
"_Alignas" to be used, not "alignas".

Which exact version of gcc do you use ?

>=20
> In any case, these changes really have to go into the UAPI header first.
> Only the __thread handling should remain.  Otherwise, we'll have a tough
> situation on our hands changing the UAPI header, without introducing
> macro definition conflicts.  I'd suggest to stick to the aligned
> attribute for the time being, like the current UAPI headers.

OK. Should I do that in a separate patch, or you do it on top of my patchse=
t,
or should I re-spin another round of the series ?
>=20
> The resut looks okay to me.
>=20
> I'm still waiting for feedback from other maintainers whether the level
> of documentation and testing is appropriate.

OK.

Thanks,

Mathieu

--=20
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com