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Date:   Mon, 25 May 2020 10:42:34 +0200
From:   Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To:     YuanJunQing <yuanjunqing66@163.com>
Cc:     paulburton@kernel.org, chenhc@lemote.com,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        liulichao@loongson.cn
Subject: Re: [PATCH] MIPS: Fix IRQ tracing when call handle_fpe()
Message-ID: <20200525084234.GA5057@alpha.franken.de>
References: <20200525033123.13114-1-yuanjunqing66@163.com>
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On Mon, May 25, 2020 at 11:31:23AM +0800, YuanJunQing wrote:
>  Register "a1" is unsaved in this function,
>  when CONFIG_TRACE_IRQFLAGS is enabled,
>  the TRACE_IRQS_OFF macro will call trace_hardirqs_off(),
>  and this may change register "a1".
>  The variment of register "a1" may send SIGFPE signal
>  to task when call do_fpe(),and this may kill the task.
> 
> Signed-off-by: YuanJunQing <yuanjunqing66@163.com>
> ---
>  arch/mips/kernel/genex.S | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> index 8236fb291e3f..956a76429773 100644
> --- a/arch/mips/kernel/genex.S
> +++ b/arch/mips/kernel/genex.S
> @@ -480,16 +480,18 @@ NESTED(nmi_handler, PT_SIZE, sp)
>  	/* gas fails to assemble cfc1 for some archs (octeon).*/ \
>  	.set	mips1
>  	SET_HARDFLOAT
> -	cfc1	a1, fcr31
> +	cfc1	s0, fcr31
>  	.set	pop
>  	CLI
>  	TRACE_IRQS_OFF
> +	move    a1,s0
>  	.endm

do we realy need to read fcr31 that early ? Wouldn't it work to
just move the cfc1 below TRACE_IRQS_OFF ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]