Re: [PATCH] RDMA/siw: Fix compiler warnings on 32-bit due to u64/pointer abuse

Geert Uytterhoeven
2019-08-19T17:15:13Z

Hi Joe,

On Mon, Aug 19, 2019 at 6:56 PM Joe Perches <joe@perches.com> wrote:
> On Mon, 2019-08-19 at 12:05 +0200, Geert Uytterhoeven wrote:
> > When compiling on 32-bit:
> >
> > drivers/infiniband/sw/siw/siw_cq.c:76:20: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> > drivers/infiniband/sw/siw/siw_qp.c:952:28: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
> []
> > Fix this by applying the following rules:
> > 1. When printing a u64, the %llx format specififer should be used,
> > instead of casting to a pointer, and printing the latter.
> > 2. When assigning a pointer to a u64, the pointer should be cast to
> > uintptr_t, not u64,
> > 3. When casting from u64 to pointer, an intermediate cast to uintptr_t
> > should be added,
>
> I think a cast to unsigned long is rather more common.
>
> uintptr_t is used ~1300 times in the kernel.
> I believe a cast to unsigned long is much more common.

That is true, as uintptr_t was introduced in C99.
Similarly, unsigned long was used before size_t became common.

However, nowadays size_t and uintptr_t are preferred.

> It might be useful to add something to the Documentation
> for this style. Documentation/process/coding-style.rst
>
> And trivia:
>
> > > diff --git a/drivers/infiniband/sw/siw/siw_verbs.c b/drivers/infiniband/sw/siw/siw_verbs.c
> []
> > @@ -842,8 +842,8 @@ int siw_post_send(struct ib_qp *base_qp, const struct ib_send_wr *wr,
> > rv = -EINVAL;
> > break;
> > }
> > - siw_dbg_qp(qp, "opcode %d, flags 0x%x, wr_id 0x%p\n",
> > - sqe->opcode, sqe->flags, (void *)sqe->id);
> > + siw_dbg_qp(qp, "opcode %d, flags 0x%x, wr_id 0x%llx\n",
> > + sqe->opcode, sqe->flags, sqe->id);
>
> Printing possible pointers as %llx is generally not a good idea
> given the desire for %p obfuscation.

Are they pointers? Difficult to know with all the casting...

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds