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SubjectRe: [PATCH 4/7] signal/mips: Document a conflict with SI_USER with SIGFPE
On Tue, 18 Jul 2017, Eric W. Biederman wrote:

> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> index b68b4d0726d3..6c9cca9c5341 100644
> --- a/arch/mips/kernel/traps.c
> +++ b/arch/mips/kernel/traps.c
> @@ -735,7 +735,7 @@ void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
> else if (fcr31 & FPU_CSR_INE_X)
> si.si_code = FPE_FLTRES;
> else
> - si.si_code = __SI_FAULT;
> + si.si_code = FPE_FIXME;

This is an "impossible" state to reach unless your hardware is on fire.
One or more of the FCSR Cause bits will have been set (in `fcr31') or the
FPE exception would not have happened.

Of course there could be a simulator bug, or we could have breakage
somewhere causing `process_fpemu_return' to be called with SIGFPE and
inconsistent `fcr31'. So we need to handle it somehow.

So what would be the right value of `si_code' to use here for such an
unexpected exception condition? I think `BUG()' would be too big a
hammer here. Or wouldn't it?

Maciej

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