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From: Michael Ellerman <mpe@ellerman.id.au>
To: Paul Murphy <murp@ibm.com>, pmenzel@molgen.mpg.de
Cc: parkerderek86@gmail.com, laboger@linux.vnet.ibm.com,
	xaionaro@gmail.com, paulus@samba.org, murphyp@linux.ibm.com,
	linuxppc-dev@lists.ozlabs.org
Subject: RE: Possible regression by ab037dd87a2f (powerpc/vdso: Switch VDSO to generic C implementation.)
Date: Mon, 02 Aug 2021 16:18:58 +1000	[thread overview]
Message-ID: <87czqwl67h.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <OF44F7146F.67A4C1C2-ON00258720.004DBF64-00258720.004FCFCC@ibm.com>

"Paul Murphy" <murp@ibm.com> writes:
>  
> (My apologies for however IBM's email client munges this)
>
>> I heard it is going to be in Go 1.16.7, but I do not know much about Go.
>> Maybe the folks in Cc can chime in.
>  
>  
> We have backports primed and ready for the next point release. They
> are waiting on the release manager to cherrypick them.

OK good, that is still the correct fix in the long run.

> I think we were aware that our VDSO usage may have exploited some
> peculiarities in how the ppc64 version was constructed (i.e hand
> written assembly which just didn't happen to clobber R30).

Yeah I was "somewhat surprised" that Go thought it could use r30 like
that across a VDSO call :D

But to be fair the ABI of the VDSO has always been a little fishy,
because the entry points pretend to be a transparent wrapper around
system calls, but then in a case like this are not.

> Go up to this point has only used the vdso function __kernel_clock_gettime; it
> is the only entry point which would need to explicitly avoid R30 for
> Go's sake.

I thought about limiting the workaround to just that code, but it seemed
silly and likely to come back to bite us. Once the compilers decides to
spill a non-volatile there are plenty of other ones to choose from.

cheers

  parent reply	other threads:[~2021-08-02  6:19 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27  8:45 Paul Menzel
2021-07-27 23:14 ` Benjamin Herrenschmidt
2021-07-28  8:26   ` Paul Menzel
2021-07-28 12:43     ` Michael Ellerman
2021-07-28 12:53       ` Paul Menzel
2021-07-29  7:41         ` Michael Ellerman
2021-07-29  8:33           ` Paul Menzel
2021-07-29 12:58             ` Michael Ellerman
     [not found]         ` <875ywt1s9r.fsf__45665.8238823124$1627544516$gmane$org@mpe.ellerman.id.au>
2021-07-29  8:48           ` Andreas Schwab
2021-08-02  6:04             ` Michael Ellerman
     [not found]       ` <OF44F7146F.67A4C1C2-ON00258720.004DBF64-00258720.004FCFCC@ibm.com>
2021-08-02  6:18         ` Michael Ellerman [this message]
2021-08-02 12:48           ` Benjamin Herrenschmidt
2021-08-02 18:07           ` Segher Boessenkool
2021-08-02 18:14           ` Lynn Boger

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