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

* Mathieu Desnoyers:

----- On Jun 3, 2020, at 8:05 AM, Florian Weimer fweimer@redhat.com wrote:

quoted

* Mathieu Desnoyers:

quoted

+#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) 

quoted

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