• Christian Brauner's avatar
    sparc64: enable HAVE_COPY_THREAD_TLS · dcad2a62
    Christian Brauner authored
    This is part of a larger series that aims at getting rid of the
    copy_thread()/copy_thread_tls() split that makes the process creation
    codepaths in the kernel more convoluted and error-prone than they need
    to be.
    It also unblocks implementing clone3() on architectures not support
    copy_thread_tls(). Any architecture that wants to implement clone3()
    will need to select HAVE_COPY_THREAD_TLS and thus need to implement
    copy_thread_tls(). So both goals are connected but independently
    beneficial.
    
    HAVE_COPY_THREAD_TLS means that a given architecture supports
    CLONE_SETTLS and not setting it should usually mean that the
    architectures doesn't implement it but that's not how things are. In
    fact all architectures support CLONE_TLS it's just that they don't
    follow the calling convention that HAVE_COPY_THREAD_TLS implies. That
    means all architectures can be switched over to select
    HAVE_COPY_THREAD_TLS. Once that is done we can remove that macro (yay,
    less code), the unnecessary do_fork() export in kernel/fork.c, and also
    rename copy_thread_tls() back to copy_thread(). At this point
    copy_thread() becomes the main architecture specific part of process
    creation but it will be the same layout and calling convention for all
    architectures. (Once that is done we can probably cleanup each
    copy_thread() function even more but that's for the future.)
    
    Since sparc does support CLONE_SETTLS there's no reason to not select
    HAVE_COPY_THREAD_TLS. This brings us one step closer to getting rid of
    the copy_thread()/copy_thread_tls() split we still have and ultimately
    the HAVE_COPY_THREAD_TLS define in general. A lot of architectures have
    already converted and sparc is one of the few hat haven't yet. This also
    unblocks implementing the clone3() syscall on sparc which I will follow
    up later (if no one gets there before me). Once that is done we can get
    of another ARCH_WANTS_* macro.
    
    This patch just switches sparc64 over to HAVE_COPY_THREAD_TLS but not
    sparc32 which will be done in the next patch. Once Any architecture that
    supports HAVE_COPY_THREAD_TLS cannot call the do_fork() helper anymore.
    This is fine and intended since it should be removed in favor of the
    new, cleaner _do_fork() calling convention based on struct
    kernel_clone_args. In fact, most architectures have already switched.
    With this patch, sparc joins the other arches which can't use the
    fork(), vfork(), clone(), clone3() syscalls directly and who follow the
    new process creation calling convention that is based on struct
    kernel_clone_args which we introduced a while back. This means less
    custom assembly in the architectures entry path to set up the registers
    before calling into the process creation helper and it is easier to to
    support new features without having to adapt calling conventions. It
    also unifies all process creation paths between fork(), vfork(),
    clone(), and clone3(). (We can't fix the ABI nightmare that legacy
    clone() is but we can prevent stuff like this happening in the future.)
    
    Note that sparc can't easily call into the syscalls directly because of
    its return value conventions when a new process is created which
    needs to clobber the UREG_I1 register in copy_thread{_tls()} and it
    needs to restore it if process creation fails. That's not a big deal
    since the new process creation calling convention makes things simpler.
    
    This removes sparc_do_fork() and replaces it with 3 clean helpers,
    sparc_fork(), sparc_vfork(), and sparc_clone(). That means a little more
    C code until the next patch unifies sparc 32bit and sparc64. It has the
    advantage that we can remove quite a bit of assembler and it makes the
    whole syscall.S process creation bits easier to read.
    The follow-up patch will remove the custom sparc_do_fork() helper for
    32bi sparc and move sparc_fork(), sparc_vfork(), and sparc_clone() into
    a common process.c file. This allows us to remove quite a bit of
    custom assembly form 32bit sparc's entry.S file too and allows to remove
    even more code because now all helpers are shared between 32bit sparc
    and sparc64 instead of having to maintain two separate sparc_do_fork()
    implementations.
    
    For some more context, please see:
    commit 606e9ad2
    Merge: ac61145a 457677c7
    Author: Linus Torvalds <torvalds@linux-foundation.org>
    Date:   Sat Jan 11 15:33:48 2020 -0800
    
        Merge tag 'clone3-tls-v5.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
    
        Pull thread fixes from Christian Brauner:
         "This contains a series of patches to fix CLONE_SETTLS when used with
          clone3().
    
          The clone3() syscall passes the tls argument through struct clone_args
          instead of a register. This means, all architectures that do not
          implement copy_thread_tls() but still support CLONE_SETTLS via
          copy_thread() expecting the tls to be located in a register argument
          based on clone() are currently unfortunately broken. Their tls value
          will be garbage.
    
          The patch series fixes this on all architectures that currently define
          __ARCH_WANT_SYS_CLONE3. It also adds a compile-time check to ensure
          that any architecture that enables clone3() in the future is forced to
          also implement copy_thread_tls().
    
          My ultimate goal is to get rid of the copy_thread()/copy_thread_tls()
          split and just have copy_thread_tls() at some point in the not too
          distant future (Maybe even renaming copy_thread_tls() back to simply
          copy_thread() once the old function is ripped from all arches). This
          is dependent now on all arches supporting clone3().
    
          While all relevant arches do that now there are still four missing:
          ia64, m68k, sh and sparc. They have the system call reserved, but not
          implemented. Once they all implement clone3() we can get rid of
          ARCH_WANT_SYS_CLONE3 and HAVE_COPY_THREAD_TLS.
    
    Note that in the meantime, m68k has already switched to the new calling
    convention.
    Signed-off-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: Guo Ren <guoren@kernel.org>
    Cc: linux-csky@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Cc: sparclinux@vger.kernel.org
    See: d95b56c7 ("openrisc: Cleanup copy_thread_tls docs and comments")
    See: 0b9f386c ("csky: Implement copy_thread_tls")
    Link: https://lore.kernel.org/r/20200512171527.570109-2-christian.brauner@ubuntu.com
    dcad2a62
process_64.c 21.2 KB