linux-kernel - Re: [PATCH 09/11] perf/imx_ddr: Fix undefined behavior due to shift overflowing the constant

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Message-ID: <20220408104739.GA27564@willie-the-truck>
Date:   Fri, 8 Apr 2022 11:47:40 +0100
From:   Will Deacon <will@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, Frank Li <Frank.li@....com>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 09/11] perf/imx_ddr: Fix undefined behavior due to shift
 overflowing the constant

On Tue, Apr 05, 2022 at 05:15:15PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Fix:
> 
>   In file included from <command-line>:0:0:
>   In function ‘ddr_perf_counter_enable’,
>       inlined from ‘ddr_perf_irq_handler’ at drivers/perf/fsl_imx8_ddr_perf.c:651:2:
>   ././include/linux/compiler_types.h:352:38: error: call to ‘__compiletime_assert_729’ \
> 	declared with attribute error: FIELD_PREP: mask is not constant
>     _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> ...
> 
> See https://lore.kernel.org/r/YkwQ6%2BtIH8GQpuct@zn.tnic for the gory
> details as to why it triggers with older gccs only.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: Frank Li <Frank.li@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: Pengutronix Kernel Team <kernel@...gutronix.de>
> Cc: Fabio Estevam <festevam@...il.com>
> Cc: NXP Linux Team <linux-imx@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
>  drivers/perf/fsl_imx8_ddr_perf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/fsl_imx8_ddr_perf.c b/drivers/perf/fsl_imx8_ddr_perf.c
> index 94ebc1ecace7..b1b2a55de77f 100644
> --- a/drivers/perf/fsl_imx8_ddr_perf.c
> +++ b/drivers/perf/fsl_imx8_ddr_perf.c
> @@ -29,7 +29,7 @@
>  #define CNTL_OVER_MASK		0xFFFFFFFE
>  
>  #define CNTL_CSV_SHIFT		24
> -#define CNTL_CSV_MASK		(0xFF << CNTL_CSV_SHIFT)
> +#define CNTL_CSV_MASK		(0xFFU << CNTL_CSV_SHIFT)

Acked-by: Will Deacon <will@...nel.org>

(let me know if you'd prefer for me to queue this directly)

Will