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

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Date:	Wed, 30 Jul 2014 23:04:20 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	Richard Henderson <rth@...ddle.net>
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

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?

> This failure can be seen in the glibc nptl/tst-eintr* tests.
>
> Reported-by: Michael Cree <mcree@...on.net.nz>
> Signed-off-by: Richard Henderson <rth@...ddle.net>
> ---
>  arch/alpha/kernel/process.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
> index 1941a07..77028d7 100644
> --- a/arch/alpha/kernel/process.c
> +++ b/arch/alpha/kernel/process.c
> @@ -278,8 +278,6 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
>  	*childregs = *regs;
>  	childregs->r0 = 0;
>  	childregs->r19 = 0;
> -	childregs->r20 = 1;	/* OSF/1 has some strange fork() semantics.  */
> -	regs->r20 = 0;
>  	stack = ((struct switch_stack *) regs) - 1;
>  	*childstack = *stack;
>  	childstack->r26 = (unsigned long) ret_from_fork;
> -- 
> 1.9.3
>

-- 
Måns Rullgård
mans@...sr.com
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