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From:   Andreas Schwab <schwab@linux-m68k.org>
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        "Luck, Tony" <tony.luck@intel.com>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        "linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Qais Yousef <qais.yousef@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ia64: enable HAVE_COPY_THREAD_TLS, switch to
 kernel_clone_args
References: <20200513204848.1208864-1-christian.brauner@ubuntu.com>
        <3908561D78D1C84285E8C5FCA982C28F7F6266E0@ORSMSX115.amr.corp.intel.com>
        <79e58d9b-5a39-390c-2f0c-0d87b63442b4@physik.fu-berlin.de>
        <20200514074606.vkc35syhdep23rzh@wittgenstein>
        <6b298416-1e64-eee7-0bb4-3b1f7f67adc6@physik.fu-berlin.de>
        <d6c94d4f-a431-9de5-7a0f-661894dbec01@physik.fu-berlin.de>
        <20200514100459.pt7dxq2faghdds2c@wittgenstein>
        <2e22b0d2-b9ce-420d-48a0-0d9134108a5c@physik.fu-berlin.de>
        <20200514101540.25hvle74w63t66fs@wittgenstein>
        <20200514101914.fu7xhgaxtb5fy2ky@wittgenstein>
Date:   Thu, 14 May 2020 12:37:03 +0200
In-Reply-To: <20200514101914.fu7xhgaxtb5fy2ky@wittgenstein> (Christian
        Brauner's message of "Thu, 14 May 2020 12:19:14 +0200")
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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@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."