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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Nicholas Piggin <npiggin@gmail.com>
Cc:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/85xx: Fix math emulation exception
In-Reply-To: <066caa6d9480365da9b8ed83692d7101e10ac5f8.1695657339.git.christophe.leroy@csgroup.eu>
References: <066caa6d9480365da9b8ed83692d7101e10ac5f8.1695657339.git.christophe.leroy@csgroup.eu>
Date:   Tue, 10 Oct 2023 21:45:10 +1100
Message-ID: <8734yisqmh.fsf@mail.lhotse>
MIME-Version: 1.0
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Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Booting mpc85xx_defconfig kernel on QEMU leads to:

What machine/CPU model are you using for that?

I tried ppce500/e500 and that is working OK for me, ie. boots to
userspace and I see math instructions being emulated via the emulated
stats.

cheers

> Bad trap at PC: fe9bab0, SR: 2d000, vector=800
> awk[82]: unhandled trap (5) at 0 nip fe9bab0 lr fe9e01c code 5 in libc-2.27.so[fe5a000+17a000]
> awk[82]: code: 3aa00000 3a800010 4bffe03c 9421fff0 7ca62b78 38a00000 93c10008 83c10008
> awk[82]: code: 38210010 4bffdec8 9421ffc0 7c0802a6 <fc00048e> d8010008 4815190d 93810030
> Trace/breakpoint trap
> WARNING: no useful console
>
> This is because allthough CONFIG_MATH_EMULATION is selected,
> Exception 800 calls unknown_exception().
>
> Call emulation_assist_interrupt() instead.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/head_85xx.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/head_85xx.S b/arch/powerpc/kernel/head_85xx.S
> index 97e9ea0c7297..0f1641a31250 100644
> --- a/arch/powerpc/kernel/head_85xx.S
> +++ b/arch/powerpc/kernel/head_85xx.S
> @@ -395,7 +395,7 @@ interrupt_base:
>  #ifdef CONFIG_PPC_FPU
>  	FP_UNAVAILABLE_EXCEPTION
>  #else
> -	EXCEPTION(0x0800, FP_UNAVAIL, FloatingPointUnavailable, unknown_exception)
> +	EXCEPTION(0x0800, FP_UNAVAIL, FloatingPointUnavailable, emulation_assist_interrupt)
>  #endif
>  
>  	/* System Call Interrupt */
> -- 
> 2.41.0