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

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Message-ID: <87blmq6bw0.fsf@igel.home>
Date:   Thu, 14 May 2020 12:37:03 +0200
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "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 Mai 14 2020, Christian Brauner wrote:

>> 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
>
> Scratch that. It's even worse. On ia64 it is _invalid_ to pass a NULL
> stack.

Only if you want CLONE_VM.  But this raw_clone does not allow CLONE_VM,
thus it is actually a true fork.

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."