Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] nvme: fix 32-bit build warning | Date | Fri, 09 Oct 2015 20:55:26 +0200 |
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On Friday 09 October 2015 07:42:21 Christoph Hellwig wrote: > On Tue, Oct 06, 2015 at 10:37:11PM +0200, Arnd Bergmann wrote: > > Compiling the nvme driver on 32-bit warns about a cast from a __u64 > > variable to a pointer: > > > > drivers/block/nvme-core.c: In function 'nvme_submit_io': > > drivers/block/nvme-core.c:1847:4: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] > > (void __user *)io.addr, length, NULL, 0); > > > > The cast here is intentional and safe, so we can shut up the > > gcc warning by adding an intermediate cast to 'unsigned long'. > > It really should be a uintptr_t, which would also avoid the > 80 > character lines. I wonder if we need a u64_to_ptr helper given these > ioctl ABIs that pass pointers as a u64 seems to be everywhere these > days.
I'll send a new version with uintptr_t for now, but having a proper interface for this sounds like a good idea.
I've seen a couple of cases like this, and most but not all actually want a __user pointer like this one. That seems similar to the common ioctl use case where we want a user pointer from an 'unsigned long', so we could use the same function for both, like
static inline void __user *get_uptr(unsigned long arg) { return (void __user *)arg; }
With this definition, you can pass any scalar type (u64 or unsigned long normally) and get the pointer, and we can put that into include/linux/uaccess.h.
Arnd
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