linux-kernel - Re: [PATCH] spi: initialize status to success

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Date:   Sat, 16 Apr 2022 16:05:57 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Tom Rix <trix@...hat.com>
Cc:     broonie@...nel.org, ndesaulniers@...gle.com,
        paul.kocialkowski@...tlin.com, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] spi: initialize status to success

On Sat, Apr 16, 2022 at 04:51:32PM -0400, Tom Rix wrote:
> Clang static analysis reports this issue
> spi.c:3583:2: warning: 2nd function call argument
>   is an uninitialized value
>   trace_spi_setup(spi, status);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> It is possible that status is never set because
> its function level setting was removed by the
> commit listed in the Fixes: tag.
> 
> Assume that setting 8 bits-per-word is ok and
> initialize the status to 0.
> 
> Fixes: b3fe2e516741 ("spi: core: Only check bits_per_word validity when explicitly provided")
> Signed-off-by: Tom Rix <trix@...hat.com>

I am very surprised that -Wsometimes-uninitialized does not trigger
here, as this instance does not require interprocedural analysis, right?
status is not passed by reference as far as I can tell and it is only
initialized in if statements now but it is unconditionally used at the
end of the function. Maybe it does not matter too much, given that
auto-initialization is turned on by default when supported.

Regardless, this fix looks fine. I do not really like initializing
variables at the top of the function as it can hide error codes but it
is always a maintainer preference anyways so:

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  drivers/spi/spi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 563a56ce34a0..890ff46c784a 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -3475,7 +3475,7 @@ static int __spi_validate_bits_per_word(struct spi_controller *ctlr,
>  int spi_setup(struct spi_device *spi)
>  {
>  	unsigned	bad_bits, ugly_bits;
> -	int		status;
> +	int		status = 0;
>  
>  	/*
>  	 * Check mode to prevent that any two of DUAL, QUAD and NO_MOSI/MISO
> -- 
> 2.27.0
>