* Mathieu Desnoyers via Libc-alpha:
> diff --git a/NEWS b/NEWS
> index 141078c319..c4e0370fc4 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -23,6 +23,16 @@ Major new features:
> toolchains. It is recommended to use GCC 8 or newer when testing
> this option.
>
> +* Support for automatically registering threads with the Linux rseq
> + system call has been added. This system call is implemented starting
> + from Linux 4.18. The Restartable Sequences ABI accelerates user-space
> + operations on per-cpu data. It allows user-space to perform updates
> + on per-cpu data without requiring heavy-weight atomic operations.
> + Automatically registering threads allows all libraries, including libc,
> + to make immediate use of the rseq(2) support by using the documented ABI.
> + The GNU C Library manual has details on integration of Restartable
> + Sequences.
“rseq” instead “rseq(2)”.
> diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
> index e6c64fb526..f0fcf6448e 100644
> --- a/elf/libc_early_init.c
> +++ b/elf/libc_early_init.c
> @@ -18,10 +18,14 @@
>
> #include <ctype.h>
> #include <libc-early-init.h>
> +#include <rseq-internal.h>
>
> void
> __libc_early_init (_Bool initial)
> {
> /* Initialize ctype data. */
> __ctype_init ();
> + /* Register rseq ABI to the kernel for the main program's libc. */
> + if (initial)
> + rseq_register_current_thread ();
> }
Okay.
> diff --git a/manual/threads.texi b/manual/threads.texi
> index 0858ef8f92..a565095c43 100644
> --- a/manual/threads.texi
> +++ b/manual/threads.texi
> @@ -9,8 +9,10 @@ This chapter describes functions used for managing threads.
> POSIX threads.
>
> @menu
> -* ISO C Threads:: Threads based on the ISO C specification.
> -* POSIX Threads:: Threads based on the POSIX specification.
> +* ISO C Threads:: Threads based on the ISO C specification.
> +* POSIX Threads:: Threads based on the POSIX specification.
> +* Restartable Sequences:: Linux-specific Restartable Sequences
> + integration.
> @end menu
This should go into the extensions menu (@node Non-POSIX Extensions).
General comment: Please wrap the lines around 72 or so characters.
Thanks.
> @@ -881,3 +883,63 @@ Behaves like @code{pthread_timedjoin_np} except that the absolute time in
> @c pthread_spin_unlock
> @c pthread_testcancel
> @c pthread_yield
> +
> +@node Restartable Sequences
> +@section Restartable Sequences
> +@cindex Restartable Sequences
> +
> +This section describes Restartable Sequences integration for
> +@theglibc{}.
“This functionality is only available on Linux.” (The @standards parts
are not visible to readers.)
> +
> +@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 (Linux-specific). 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.
Can drop “(Linux-specific)” here.
> diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h b/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h
> new file mode 100644
> index 0000000000..37d83fcb4a
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/aarch64/bits/rseq.h
> +#ifdef __AARCH64EB__
> +#define RSEQ_SIG_DATA 0x00bc28d4 /* BRK #0x45E0. */
> +#else
> +#define RSEQ_SIG_DATA RSEQ_SIG_CODE
> +#endif
Missing indentation on the #defines (sorry!).
> diff --git a/sysdeps/unix/sysv/linux/arm/bits/rseq.h b/sysdeps/unix/sysv/linux/arm/bits/rseq.h
> new file mode 100644
> index 0000000000..c132f0327c
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/arm/bits/rseq.h
> +#ifdef __ARMEB__
> +#define RSEQ_SIG 0xf3def5e7 /* udf #24035 ; 0x5de3 (ARMv6+) */
> +#else
> +#define RSEQ_SIG 0xe7f5def3 /* udf #24035 ; 0x5de3 */
> +#endif
Likewise, missing indentation.
> diff --git a/sysdeps/unix/sysv/linux/bits/rseq.h b/sysdeps/unix/sysv/linux/bits/rseq.h
> new file mode 100644
> index 0000000000..014c08fe0f
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/bits/rseq.h
> @@ -0,0 +1,29 @@
> +/* RSEQ_SIG is a signature required before each abort handler code.
> +
> + It is a 32-bit value that maps to actual architecture code compiled
> + into applications and libraries. It needs to be defined for each
> + architecture. When choosing this value, it needs to be taken into
> + account that generating invalid instructions may have ill effects on
> + tools like objdump, and may also have impact on the CPU speculative
> + execution efficiency in some cases. */
I wonder if we should say something somewhere that the correct way to
check for compile-time rseq support in glibc is something like this?
#if __has_include (<sys/rseq.h>)
# include <sys/rseq.h>
#endif
#ifdef RSEQ_SIG
…
#endif
Or perhaps we should suppress installation of the headers if we only
have support for the stub.
(I think this fine tuning can be deferred to later patch.)
> diff --git a/sysdeps/unix/sysv/linux/mips/bits/rseq.h b/sysdeps/unix/sysv/linux/mips/bits/rseq.h
> new file mode 100644
> index 0000000000..cbad4290cc
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/mips/bits/rseq.h
> @@ -0,0 +1,62 @@
> +#if defined(__nanomips__)
> +# ifdef __MIPSEL__
> +# define RSEQ_SIG 0x03500010
> +# else
> +# define RSEQ_SIG 0x00100350
> +# endif
> +#elif defined(__mips_micromips)
> +# ifdef __MIPSEL__
> +# define RSEQ_SIG 0xd4070000
> +# else
> +# define RSEQ_SIG 0x0000d407
> +# endif
> +#elif defined(__mips__)
> +# define RSEQ_SIG 0x0350000d
> +#else
> +/* Unknown MIPS architecture. */
> +#endif
Please use “defined (”, with a space.
> diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
> new file mode 100644
> index 0000000000..6583691285
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/rseq-internal.h
> +#ifdef RSEQ_SIG
> +static inline void
> +rseq_register_current_thread (void)
> + if (msg)
> + __libc_fatal (msg);
> + }
“if (msg != NULL)”, please.
> +#else
> +static inline void
> +rseq_register_current_thread (void)
> +{
> +}
> +#endif
Maybe add /* RSEQ_SIG */ comments to #else/#endif here as well.
> diff --git a/sysdeps/unix/sysv/linux/sys/rseq.h b/sysdeps/unix/sysv/linux/sys/rseq.h
> new file mode 100644
> index 0000000000..ea51194bf8
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/sys/rseq.h
> +#ifdef __has_include
> +# if __has_include ("linux/rseq.h")
> +# define __GLIBC_HAVE_KERNEL_RSEQ
> +# endif
> +#else
> +# include <linux/version.h>
> +# if LINUX_VERSION_CODE >= KERNEL_VERSION (4, 18, 0)
> +# define __GLIBC_HAVE_KERNEL_RSEQ
> +# endif
> +#endif
Too much indentation on the define line, I think.
Still missing: #ifdef __ASSEMBLER__. .S files should be able to include
<sys/rseq.h> to get the definition of RSEQ_SIG. But I think this can be
deferred to a follow-up.
> +#ifdef __GLIBC_HAVE_KERNEL_RSEQ
> +/* We use the structures declarations from the kernel headers. */
> +# include <linux/rseq.h>
> +#else
> +/* We use a copy of the include/uapi/linux/rseq.h kernel header. */
This comment is not true, the kernel headers do not have uptr support.
If we revert the uptr change, we also need to update the manual, I
think.
> +/* Ensure the compiler supports __attribute__ ((aligned)). */
> +_Static_assert (__alignof__ (struct rseq_cs) >= 32, "alignment");
> +_Static_assert (__alignof__ (struct rseq) >= 32, "alignment");
This needs #ifndef __cplusplus or something like that. I'm surprised
that this passes the installed header tests.
> +/* Allocations of struct rseq and struct rseq_cs on the heap need to
> + be aligned on 32 bytes. Therefore, use of malloc is discouraged
> + because it does not guarantee alignment. posix_memalign should be
> + used instead. */
> +
> +extern __thread struct rseq __rseq_abi
> + __attribute__ ((tls_model ("initial-exec")));
Should be __tls_model__.
We're getting really close now. 8-)
Thanks,
Florian
