linux-kernel - Re: [PATCH] accel/qaic: initialize ret variable to 0

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Message-ID: <fe7da2c1-904e-ee4f-9a6c-443049c214b7@quicinc.com>
Date:   Tue, 18 Apr 2023 14:46:33 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Tom Rix <trix@...hat.com>, <ogabbay@...nel.org>,
        <nathan@...nel.org>, <ndesaulniers@...gle.com>,
        <jacek.lawrynowicz@...ux.intel.com>, <quic_carlv@...cinc.com>,
        <stanislaw.gruszka@...ux.intel.com>, <quic_pkanojiy@...cinc.com>
CC:     <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>
Subject: Re: [PATCH] accel/qaic: initialize ret variable to 0

On 4/18/2023 1:20 PM, Tom Rix wrote:
> clang static analysis reports
> drivers/accel/qaic/qaic_data.c:610:2: warning: Undefined or garbage
>    value returned to caller [core.uninitialized.UndefReturn]
>          return ret;
>          ^~~~~~~~~~
> 
> The ret variable is only set some of the time but is always returned.
> So initialize ret to 0.

This does not appear to be entirely accurate to me.

Do you know what analysis Clang is doing?  Is it limited to the function 
itself?

remap_pfn_range, which initializes ret, will always run at-least once.

Feels more accurate to say that Clang cannot detect that ret will be 
initialized, and we want to quiet the warning from the false positive.

> Fixes: ff13be830333 ("accel/qaic: Add datapath")
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>   drivers/accel/qaic/qaic_data.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/accel/qaic/qaic_data.c b/drivers/accel/qaic/qaic_data.c
> index c0a574cd1b35..b46a16fb3080 100644
> --- a/drivers/accel/qaic/qaic_data.c
> +++ b/drivers/accel/qaic/qaic_data.c
> @@ -591,7 +591,7 @@ static int qaic_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struc
>   	struct qaic_bo *bo = to_qaic_bo(obj);
>   	unsigned long offset = 0;
>   	struct scatterlist *sg;
> -	int ret;
> +	int ret = 0;
>   
>   	if (obj->import_attach)
>   		return -EINVAL;