linux-kernel - Re: [PATCH 1/2] arch: mark syscall number 435 reserved for clone3

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Date:   Fri, 19 Jul 2019 21:13:16 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christian Brauner <christian@...uner.io>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        linux-kernel@...r.kernel.org, arnd@...db.de,
        linux-arch@...r.kernel.org, linux-alpha@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH 1/2] arch: mark syscall number 435 reserved for clone3

Christian Brauner <christian@...uner.io> writes:
> On Fri, Jul 19, 2019 at 08:18:02PM +1000, Michael Ellerman wrote:
>> Christian Brauner <christian@...uner.io> writes:
>> > On Mon, Jul 15, 2019 at 03:56:04PM +0200, Christian Borntraeger wrote:
>> >> I think Vasily already has a clone3 patch for s390x with 435. 
>> >
>> > A quick follow-up on this. Helge and Michael have asked whether there
>> > are any tests for clone3. Yes, there will be and I try to have them
>> > ready by the end of the this or next week for review. In the meantime I
>> > hope the following minimalistic test program that just verifies very
>> > very basic functionality (It's not pretty.) will help you test:
>> 
>> Hi Christian,
>> 
>> Thanks for the test.
>> 
>> This actually oopses on powerpc, it hits the BUG_ON in CHECK_FULL_REGS
>> in process.c around line 1633:
>> 
>> 	} else {
>> 		/* user thread */
>> 		struct pt_regs *regs = current_pt_regs();
>> 		CHECK_FULL_REGS(regs);
>> 		*childregs = *regs;
>> 		if (usp)
>> 
>> 
>> So I'll have to dig into how we fix that before we wire up clone3.
>> 
>> Turns out testing is good! :)
>
> Indeed. I have a test-suite for clone3 in mind and I hope to have it
> ready by the end of next week. It's just always the finding the time
> part that is annoying. :)

I know the feeling!

> Thanks for digging into this, Michael!

No worries, happy to help where I can.

In the intervening five minutes I remembered how we handle this, we just
need a little wrapper to save the non-volatile regs:

_GLOBAL(ppc_clone3)
	bl	save_nvgprs
	bl	sys_clone3
	b	.Lsyscall_exit


A while back I meant to make it generate those automatically based on a
flag in the syscall.tbl but of course haven't got around to it :)

So with the above it seems all good:

$ ./clone3 ; echo $?
Parent process received child's pid 4204 as return value
Parent process received child's pidfd 3
Parent process received child's pid 4204 as return argument
Child process with pid 4204
0

I'll send a patch to wire it up on Monday.

cheers