linux-kernel - Re: [PATCH] ia64: enable HAVE_COPY_THREAD_TLS, switch to kernel_clone

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Date:   Thu, 14 May 2020 12:15:40 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Qais Yousef <qais.yousef@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ia64: enable HAVE_COPY_THREAD_TLS, switch to
 kernel_clone_args

On Thu, May 14, 2020 at 12:08:27PM +0200, John Paul Adrian Glaubitz wrote:
> On 5/14/20 12:04 PM, Christian Brauner wrote:
> > So that's interesting because systemd doesn't support itanium correctly afaict.
> > They have a raw_clone() function that they use which is not tailored to
> > ia64. __NR_clone should be defined as so to hit clone2() but they don't
> > pass a stack size argument down which is invalid on ia64:
> Ah, I wasn't aware of this limitation. I'm surprised the systemd testsuite passes
> then on ia64.
> 
> On sparc64, Michael Karcher provided the hand-written assembly you quoted to
> fix the raw_clone() on this architecture.
> 
> I assume we could do the same on ia64?

I think the following should be correct:

(Probably worth checking that __NR_clone and __NR_clone2 are the same
for ia64. Also note, that __NR_clone was _never_ supported by glibc on
ia64. They even have this comment:

/* clone is not supported under Linux/ia64, use clone2. */
)

static inline pid_t raw_clone(unsigned long flags) {
        pid_t ret;

        assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
                         CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
        /* On s390/s390x and cris the order of the first and second arguments
         * of the raw clone() system call is reversed. */
        ret = (pid_t) syscall(__NR_clone, NULL, flags);
#elif defined(__sparc__)
        {
                /**
                 * sparc always returns the other process id in %o0, and
                 * a boolean flag whether this is the child or the parent in
                 * %o1. Inline assembly is needed to get the flag returned
                 * in %o1.
                 */
                int in_child, child_pid, error;

                asm volatile("mov %3, %%g1\n\t"
                             "mov %4, %%o0\n\t"
                             "mov 0 , %%o1\n\t"
#if defined(__arch64__)
                             "t 0x6d\n\t"
#else
                             "t 0x10\n\t"
#endif
                             "addx %%g0, 0, %2\n\t"
                             "mov %%o1, %0\n\t"
                             "mov %%o0, %1" :
                             "=r"(in_child), "=r"(child_pid), "=r"(error) :
                             "i"(__NR_clone), "r"(flags) :
                             "%o1", "%o0", "%g1", "cc" );

                if (error) {
                        errno = child_pid;
                        ret = -1;
                } else
                        ret = in_child ? 0 : child_pid;
        }
+#elif defined(__ia64__)
+	/* On ia64 the stack and stack size are passed as separate arguments. */
+	return (pid_t)syscall(__NR_clone, flags, NULL, 0);
+#else
+	return (pid_t)syscall(__NR_clone, flags, NULL);
+#endif

        if (ret == 0)
                reset_cached_pid();

        return ret;
}