Re: [PATCH 1/3] glibc: Perform rseq registration at C startup and thread creation (v21)

From: Florian Weimer <fweimer@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Carlos O'Donell <carlos@redhat.com>,
	Joseph Myers <joseph@codesourcery.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	libc-alpha@sourceware.org, Thomas Gleixner <tglx@linutronix.de>,
	Ben Maurer <bmaurer@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <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@vger.kernel.org, linux-api@vger.kernel.org
Subject: Re: [PATCH 1/3] glibc: Perform rseq registration at C startup and thread creation (v21)
Date: Wed, 24 Jun 2020 16:20:47 +0200	[thread overview]
Message-ID: <87d05obl4w.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20200622180803.1449-2-mathieu.desnoyers@efficios.com> (Mathieu Desnoyers's message of "Mon, 22 Jun 2020 14:08:01 -0400")

* Mathieu Desnoyers:

> diff --git a/manual/threads.texi b/manual/threads.texi
> index bb7a42c655..d5069d5581 100644
> --- a/manual/threads.texi
> +++ b/manual/threads.texi

> +@deftypevar {struct rseq} __rseq_abi
> +@standards{Linux, sys/rseq.h}
> +@Theglibc{} implements a @code{__rseq_abi} TLS symbol to interact with
> +the Restartable Sequences system call.  The layout of this structure is
> +defined by the @file{sys/rseq.h} header.  Registration of each thread's
> +@code{__rseq_abi} is performed by @theglibc{} at library initialization
> +and thread creation. The manual for the rseq system call can be found
> +at @uref{https://git.kernel.org/pub/scm/libs/librseq/librseq.git/tree/doc/man/rseq.2}.

Should be “creation.  The” (two spaces after a sentence-ending period).

> diff --git a/sysdeps/unix/sysv/linux/sys/rseq.h b/sysdeps/unix/sysv/linux/sys/rseq.h
> new file mode 100644
> index 0000000000..5e118c1781
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/sys/rseq.h

> +#ifdef __cplusplus
> +# if  __cplusplus >= 201103L
> +#  define __rseq_static_assert(expr, diagnostic) static_assert (expr, diagnostic)
> +#  define __rseq_alignof(type)                   alignof (type)
> +#  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_tls_storage_class                _Thread_local
> +#endif
> +
> +#ifndef __rseq_static_assert
> +/* Try to use _Static_assert macro from sys/cdefs.h.  */
> +# ifdef _Static_assert
> +#  define __rseq_static_assert(expr, diagnostic) _Static_assert (expr, diagnostic)
> +# else
> +#  define __rseq_static_assert(expr, diagnostic) /* Nothing.  */
> +# endif
> +#endif
> +
> +/* Rely on GNU extensions for older standards and tls model.  */
> +#ifdef __GNUC__
> +# ifndef __rseq_alignof
> +#  define __rseq_alignof(x) __alignof__ (x)
> +# endif
> +# define __rseq_tls_model_ie __attribute__ ((__tls_model__ ("initial-exec")))
> +#else
> +/* Specifying the TLS model on the declaration is optional.  */
> +# define __rseq_tls_model_ie /* Nothing.  */
> +#endif

I'm still worried that __rseq_static_assert and __rseq_alignof will show
up in the UAPI with textually different definitions.  (This does not
apply to __rseq_tls_model_ie.)

Is my worry unfounded?

Thanks,
Florian