Messages in this thread | | | From | Alexander Potapenko <> | Date | Tue, 14 Jun 2022 20:07:52 +0200 | Subject | Re: [PATCH] [RFC] Initialization of unused function parameters |
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On Tue, Jun 14, 2022 at 6:48 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Tue, Jun 14, 2022 at 7:49 AM Alexander Potapenko <glider@google.com> wrote: > > > > The bigger question I want to raise here is whether we want to > > discourage passing uninitialized variables to functions in the kernel > > altogether. > > I'm assuming you mean pass by reference.
No, sorry for being unclear. I mean passing by value. 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.
Does that change anything?
> Some functions are really fundamentally about initializing things, and > expect uninitialized allocations.
Agreed, there are a lot of functions around that initialize one struct or another, they are out of the scope.
> What I think might be a good model is to be able to mark such > arguments as "must be initialized by callee".
This sounds interesting. In the given example I would suggest that the call to lookup_fast() (https://elixir.bootlin.com/linux/latest/source/fs/namei.c#L2016) should be initializing &inode and &seq, so that it is guaranteed that they are passed initialized into step_into().
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