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From: Michael Ellerman <>
To: Paul Murphy <>,
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: <> (raw)
In-Reply-To: <>

"Paul Murphy" <> 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.


  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$>
2021-07-29  8:48           ` Andreas Schwab
2021-08-02  6:04             ` Michael Ellerman
     [not found]       ` <>
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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