Re: [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v20)

Florian Weimer
2020-06-03T12:32:13Z

* Mathieu Desnoyers:

> ----- On Jun 3, 2020, at 8:05 AM, Florian Weimer fweimer@redhat.com wrote:
>
>> * Mathieu Desnoyers:
>>
>>> +#ifdef __cplusplus
>>> +# if __cplusplus >= 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) >= 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
>>
>> This does not seem to work. I get this with GCC 9:
>>
>> In file included from /tmp/cih_test_gsrKbC.cc:8:0:
>> ../sysdeps/unix/sysv/linux/sys/rseq.h:42:50: error: attribute ignored
>> [-Werror=attributes]
>> # define __rseq_alignas(x) alignas (x)
>> ^
>> ../sysdeps/unix/sysv/linux/sys/rseq.h:122:14: note: in expansion of macro
>> ‘__rseq_alignas’
>> 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 ?

C++ code. CXX was set to this compiler at configure time:

gcc version 9.3.1 20200408 (Red Hat 9.3.1-2) (GCC)

>> 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 patchset,
> or should I re-spin another round of the series ?

I think the initial commit should mirror the current UAPI header
contents.

Keep the macros for the UAPI patch though. 8-) We can pick up these
changes once they have been merged into Linux.

Thanks,
Florian