[PATCH 4/7] signal/mips: Document a conflict with SI_USER with SIGFPE
Eric W. Biederman
ebiederm at xmission.com
Tue Aug 8 15:29:18 UTC 2017
"Maciej W. Rozycki" <macro at imgtec.com> writes:
> 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;
>> - 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?
The possible solutions I can think of are:
WARN_ON_ONCE with a comment.
Add a new si_code to uapi/asm-generic/siginfo.h perhaps FPE_IMPOSSIBLE.
Like syscall numbers si_codes are cheap.
Call force_sig() instead of force_sig_info, using just a generic
If this is truly impossible and the compiler doesn't complain just drop
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