Re: [PATCH 1/2] alpha: Remove "strange" OSF/1 fork semantics
From: Måns Rullgård
Date: Wed Jul 30 2014 - 18:04:26 EST
Richard Henderson <rth@xxxxxxxxxxx> 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@xxxxxxxxxxxx>
> Signed-off-by: Richard Henderson <rth@xxxxxxxxxxx>
> 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;
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