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

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Message-ID: <CAKwvOdmFGVPddi98yt22i+U+3aow+dwhxKgdJ45h3n1i-n3bzw@mail.gmail.com>
Date:   Tue, 18 Apr 2023 13:48:17 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jeffrey Hugo <quic_jhugo@...cinc.com>
Cc:     Tom Rix <trix@...hat.com>, ogabbay@...nel.org, nathan@...nel.org,
        jacek.lawrynowicz@...ux.intel.com, quic_carlv@...cinc.com,
        stanislaw.gruszka@...ux.intel.com, quic_pkanojiy@...cinc.com,
        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 Tue, Apr 18, 2023 at 1:46 PM Jeffrey Hugo <quic_jhugo@...cinc.com> wrote:
>
> 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.

What happens if the loop body is never executed, say if `bo->sgt->sgl` is NULL?

>
> 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;
>


-- 
Thanks,
~Nick Desaulniers