Re: [PATCH v4 0/6] Optimize posix_spawn signal setup with clone3

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

Carlos, do we still want this for 2.37?

On 12/01/23 10:58, Adhemerval Zanella 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.  The clone3
> for x86_64 is change to not align the stack, since this is not
> async-signal safe (although current calls does mask/unmask signals).
> 
> * Changes from v3:
>   - Changes commit message and comments wording.
>   - Removed powerpc, s390x, riscv, arm, and mips clone3 optimizations.
> 
> * Changes from v2:
>   - Improve clone3 internal documentation.
> 
> * Changes from v1:
>   - Extend clone3 documentation.
>   - Remove x86_64 stack alignment on clone3 child.
>   - Fixed powerpc64 missing initial stack frame.
>   - Fixed missing save/restore r7 for arm.
> 
> Adhemerval Zanella (6):
>   linux: Do not reset signal handler in posix_spawn if it is already
>     SIG_DFL
>   linux: Extend internal clone3 documentation
>   Linux: Do not align the stack for __clone3
>   linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn
>   aarch64: Add the clone3 wrapper
>   Linux: optimize clone3 internal usage
> 
>  include/clone_internal.h                      |  37 +++-
>  posix/Makefile                                |   3 +-
>  posix/tst-spawn7.c                            | 179 ++++++++++++++++++
>  sysdeps/unix/sysv/linux/Makefile              |   3 +-
>  sysdeps/unix/sysv/linux/aarch64/clone3.S      |  85 +++++++++
>  sysdeps/unix/sysv/linux/aarch64/sysdep.h      |   2 +
>  sysdeps/unix/sysv/linux/clone-internal.c      |  59 ++++--
>  sysdeps/unix/sysv/linux/clone3.h              |  15 +-
>  sysdeps/unix/sysv/linux/kernel-features.h     |   9 +
>  sysdeps/unix/sysv/linux/spawni.c              |  33 +++-
>  .../sysv/linux/tst-misalign-clone-internal.c  |  74 --------
>  sysdeps/unix/sysv/linux/x86_64/clone3.S       |   3 -
>  12 files changed, 384 insertions(+), 118 deletions(-)
>  create mode 100644 posix/tst-spawn7.c
>  create mode 100644 sysdeps/unix/sysv/linux/aarch64/clone3.S
>  delete mode 100644 sysdeps/unix/sysv/linux/tst-misalign-clone-internal.c
>