linux-kernel - Re: [PATCH] spi: rockchip: avoid objtool warning

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Message-ID: <20210226081548.h5ls5fxihunzxjvx@ti.com>
Date:   Fri, 26 Feb 2021 13:45:48 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Arnd Bergmann <arnd@...nel.org>
CC:     Mark Brown <broonie@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Arnd Bergmann <arnd@...db.de>,
        Jon Lin <jon.lin@...k-chips.com>,
        Chris Ruehl <chris.ruehl@...ys.com.hk>,
        Alexander Kochetkov <al.kochet@...il.com>,
        Johan Jonker <jbx6244@...il.com>,
        Vincent Pelletier <plr.vincent@...il.com>,
        <linux-spi@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] spi: rockchip: avoid objtool warning

Hi,

On 25/02/21 01:55PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Building this file with clang leads to a an unreachable code path
> causing a warning from objtool:
> 
> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
> 
> Use BUG() instead of unreachable() to avoid the undefined behavior
> if it does happen.
> 
> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/spi/spi-rockchip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index 936ef54e0903..972beac1169a 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
>  		 * ctlr->bits_per_word_mask, so this shouldn't
>  		 * happen
>  		 */
> -		unreachable();
> +		BUG();

checkpatch says:

  Avoid crashing the kernel - try using WARN_ON & recovery code rather 
  than BUG() or BUG_ON()

Which makes sense to me. This is not something bad enough to justify 
crashing the kernel.

>  	}
>  
>  	if (use_dma) {
> -- 
> 2.29.2
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.