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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 14 Jun 2022 11:30:47 -0700
Message-ID: <CAHk-=whjz3wO8zD+itoerphWem+JZz4uS3myf6u1Wd6epGRgmQ@mail.gmail.com>
Subject: Re: [PATCH] [RFC] Initialization of unused function parameters
To:     Alexander Potapenko <glider@google.com>
Cc:     Evgenii Stepanov <eugenis@google.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vitaly Buka <vitalybuka@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-toolchains <linux-toolchains@vger.kernel.org>
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On Tue, Jun 14, 2022 at 11:08 AM Alexander Potapenko <glider@google.com> wrote:
>
> On Tue, Jun 14, 2022 at 6:48 PM Linus Torvalds
> >
> > I'm assuming you mean pass by reference.
>
> No, sorry for being unclear. I mean passing by value.

Pass-by-value most definitely should warn about uninitialized variables.

> In the given example the prototype of step_into looks as follows (see
> https://elixir.bootlin.com/linux/latest/source/fs/namei.c#L1846):
>
>   static const char *step_into(struct nameidata *nd, int flags, struct
> dentry *dentry, struct inode *inode, unsigned seq);
>
> , and the local variables `struct inode *inode` and `unsigned seq` are
> being passed to it by value, i.e. in certain cases the struct inode
> pointer and the unsigned seq are uninitialized.

Then those cases should warn. No question about it.

I assume the only reason they don't warn right now is that the
compiler doesn't see that they are uninitialized, possibly due to some
earlier pass-by-reference use.

             Linus