nios2: enable HAVE_COPY_THREAD_TLS, switch to kernel_clone_args
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. I'm converting all the remaining arches that haven't yet switched and am collecting individual acks. Once I have them, I'll send the whole series removing the copy_thread()/copy_thread_tls() split, the HAVE_COPY_THREAD_TLS define and the legacy do_fork() helper. The only kernel-wide process creation entry point for anything not going directly through the syscall path will then be based on struct kernel_clone_args. No more danger of weird process creation abi quirks between architectures hopefully, and easier to maintain overall. 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 nios2 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 nios2 is one of the few hat haven't yet. This also unblocks implementing the clone3() syscall on nios2. Once that is done we can get of another ARCH_WANTS_* macro. 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, nios2 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.) 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. And I've got sparc patches acked by Dave and ia64 is already done too. You can find a link to a booting qemu nios2 system with all the changes here at [1]. [1]: https://asciinema.org/a/333353 Cc: linux-kernel@vger.kernel.org Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by:Ley Foon Tan <ley.foon.tan@intel.com> Signed-off-by:
Christian Brauner <christian.brauner@ubuntu.com>
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