Re: [PATCH v2 0/9] Optimize posix_spawn signal setup with clone3

[Carlos O'Donell <carlos@redhat.com>]

On 9/30/22 15:26, Adhemerval Zanella via Libc-alpha wrote:
> Currently posix_spawn has to issue at least NSIG sigaction syscalls
> to obtain current signal disposition and more if they there are not
> either SIG_IGN or SIG_DFL.  The new clone3 CLONE_CLEAR_SIGHAND flags
> introduced with Linux 5.5 resets all signal handlers of the child not
> set to SIG_IGN to SIG_DFL, thus allowing posix_spawn to skip this
> preparation phase.
> 
> The exception is the signals defined by posix_spawnattr_setsigdefault
> when POSIX_SPAWN_SETSIGDEF is set (since they can be SIG_IGN).  In
> this case posix_spawn helper process needs to issue a sigction to 
> set the signal disposition to SIG_DFL.
> 
> The patchset also adds clone3 implementation for aarch64, powerpc64,
> s390x, riscv, arm, and mips.
> 

I would like to trim this down for glibc 2.37.

I think we can get the default implementation in place and enable this for x86_64.

Everything else that adds custom assembly should be something we commit once 2.38
opens and so we can have time to review the generated code and make sure we don't
break anything.

I'd like to see a v3 posted with just the 3 patches required to turn this on:
1/9 linux: Do not reset signal handler in posix_spawn if it is already SIG_DFL
2/9 linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn
9/9 Linux: optimize clone3 internal usage

> Changes from v1:
>   * Adeed arm and mips clone3 implementation.
> 
> Adhemerval Zanella (9):
>   linux: Do not reset signal handler in posix_spawn if it is already
>     SIG_DFL
>   linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn
>   powerpc64le: Add the clone3 wrapper
>   aarch64: Add the clone3 wrapper
>   s390x: Add the clone3 wrapper
>   riscv: Add the clone3 wrapper
>   arm: Add the clone3 wrapper
>   mips: Add the clone3 wrapper
>   Linux: optimize clone3 internal usage
> 
>  include/clone_internal.h                      |  10 +
>  posix/Makefile                                |   3 +-
>  posix/tst-spawn7.c                            | 179 ++++++++++++++++++
>  sysdeps/unix/sysv/linux/aarch64/clone3.S      |  90 +++++++++
>  sysdeps/unix/sysv/linux/aarch64/sysdep.h      |   2 +
>  sysdeps/unix/sysv/linux/arm/clone3.S          |  80 ++++++++
>  sysdeps/unix/sysv/linux/arm/sysdep.h          |   1 +
>  sysdeps/unix/sysv/linux/clone-internal.c      |  59 ++++--
>  sysdeps/unix/sysv/linux/clone3.h              |   6 +
>  sysdeps/unix/sysv/linux/kernel-features.h     |   9 +
>  sysdeps/unix/sysv/linux/mips/clone3.S         | 147 ++++++++++++++
>  sysdeps/unix/sysv/linux/mips/sysdep.h         |   2 +
>  .../sysv/linux/powerpc/powerpc64/clone3.S     | 145 ++++++++++++++
>  sysdeps/unix/sysv/linux/powerpc/sysdep.h      |   1 +
>  sysdeps/unix/sysv/linux/riscv/clone3.S        |  83 ++++++++
>  sysdeps/unix/sysv/linux/riscv/sysdep.h        |   1 +
>  sysdeps/unix/sysv/linux/s390/s390-64/clone3.S |  84 ++++++++
>  sysdeps/unix/sysv/linux/s390/sysdep.h         |   1 +
>  sysdeps/unix/sysv/linux/spawni.c              |  33 +++-
>  19 files changed, 910 insertions(+), 26 deletions(-)
>  create mode 100644 posix/tst-spawn7.c
>  create mode 100644 sysdeps/unix/sysv/linux/aarch64/clone3.S
>  create mode 100644 sysdeps/unix/sysv/linux/arm/clone3.S
>  create mode 100644 sysdeps/unix/sysv/linux/mips/clone3.S
>  create mode 100644 sysdeps/unix/sysv/linux/powerpc/powerpc64/clone3.S
>  create mode 100644 sysdeps/unix/sysv/linux/riscv/clone3.S
>  create mode 100644 sysdeps/unix/sysv/linux/s390/s390-64/clone3.S
> 

-- 
Cheers,
Carlos.