linux-kernel - Re: [PATCH 1/2] alpha: Remove "strange" OSF/1 fork semantics

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Date:	Wed, 30 Jul 2014 13:07:10 -1000
From:	Richard Henderson <rth@...ddle.net>
To:	Måns Rullgård <mans@...sr.com>
CC:	linux-kernel@...r.kernel.org, mcree@...on.net.nz,
	linux-alpha@...r.kernel.org
Subject: Re: [PATCH 1/2] alpha: Remove "strange" OSF/1 fork semantics

On 07/30/2014 12:04 PM, Måns Rullgård wrote:
> Richard Henderson <rth@...ddle.net> writes:
> 
>> The assignment to regs->r20 kills the original tls_val input
>> to the clone syscall, which means that clone can no longer be
>> restarted with the original inputs.
>>
>> We could, perhaps, retain this result for true fork, but OSF/1
>> compatibility is no longer important.  Note that glibc has never
>> used the r20 result value, instead always testing r0 vs 0 to
>> determine the child/parent status.
> 
> What effect does this have on OSF/1 compat?

I don't know, as I've never had access to osf/1 myself.  It depends on how that
$20 value is used -- potentially, fork(3) no longer works.

I can imagine that we could retain these assignments under the condition of
clone_flags == 0, which both implies a basic fork as well as the fact that the
tls_val argument is unused.

But I do have to ask first if anyone actually cares.  Surely the amount of
osf-on-linux emulation is a vanishingly small proportion of the already small
alpha-linux population.

r~
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