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Subject[PATCH] nios2: enable HAVE_COPY_THREAD_TLS, switch to kernel_clone_args
Date
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 606e9ad20094f6d500166881d301f31a51bc8aa7
Merge: ac61145a725a 457677c70c76
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>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
arch/nios2/Kconfig | 1 +
arch/nios2/kernel/entry.S | 7 +------
arch/nios2/kernel/process.c | 26 +++++++++++++++++++++++---
3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index c6645141bb2a..f9a05957a883 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -27,6 +27,7 @@ config NIOS2
select USB_ARCH_HAS_HCD if USB_SUPPORT
select CPU_NO_EFFICIENT_FFS
select MMU_GATHER_NO_RANGE if MMU
+ select HAVE_COPY_THREAD_TLS

config GENERIC_CSUM
def_bool y
diff --git a/arch/nios2/kernel/entry.S b/arch/nios2/kernel/entry.S
index 3d8d1d0bcb64..da8442450e46 100644
--- a/arch/nios2/kernel/entry.S
+++ b/arch/nios2/kernel/entry.S
@@ -389,12 +389,7 @@ ENTRY(ret_from_interrupt)
*/
ENTRY(sys_clone)
SAVE_SWITCH_STACK
- addi sp, sp, -4
- stw r7, 0(sp) /* Pass 5th arg thru stack */
- mov r7, r6 /* 4th arg is 3rd of clone() */
- mov r6, zero /* 3rd arg always 0 */
- call do_fork
- addi sp, sp, 4
+ call nios2_clone
RESTORE_SWITCH_STACK
ret

diff --git a/arch/nios2/kernel/process.c b/arch/nios2/kernel/process.c
index 509e7855e8dc..5f5c3c926bd1 100644
--- a/arch/nios2/kernel/process.c
+++ b/arch/nios2/kernel/process.c
@@ -100,8 +100,8 @@ void flush_thread(void)
{
}

-int copy_thread(unsigned long clone_flags,
- unsigned long usp, unsigned long arg, struct task_struct *p)
+int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
+ unsigned long arg, struct task_struct *p, unsigned long tls)
{
struct pt_regs *childregs = task_pt_regs(p);
struct pt_regs *regs;
@@ -140,7 +140,7 @@ int copy_thread(unsigned long clone_flags,

/* Initialize tls register. */
if (clone_flags & CLONE_SETTLS)
- childstack->r23 = regs->r8;
+ childstack->r23 = tls;

return 0;
}
@@ -259,3 +259,23 @@ int dump_fpu(struct pt_regs *regs, elf_fpregset_t *r)
{
return 0; /* Nios2 has no FPU and thus no FPU registers */
}
+
+asmlinkage int nios2_clone(unsigned long clone_flags, unsigned long newsp,
+ int __user *parent_tidptr, int __user *child_tidptr,
+ unsigned long tls)
+{
+ struct kernel_clone_args args = {
+ .flags = (lower_32_bits(clone_flags) & ~CSIGNAL),
+ .pidfd = parent_tidptr,
+ .child_tid = child_tidptr,
+ .parent_tid = parent_tidptr,
+ .exit_signal = (lower_32_bits(clone_flags) & CSIGNAL),
+ .stack = newsp,
+ .tls = tls,
+ };
+
+ if (!legacy_clone_args_valid(&args))
+ return -EINVAL;
+
+ return _do_fork(&args);
+}
base-commit: b9bbe6ed63b2b9f2c9ee5cbd0f2c946a2723f4ce
--
2.26.2

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