Re: [PATCH] x86: Fixes warning: cast removes address space '__user' of expression in uaccess_64.h

[Dave Hansen]

On 11/16/23 09:38, Dipendra Khadka wrote:
> Sparse has identified a warning as follows:
> 
> ./arch/x86/include/asm/uaccess_64.h:88:24: warning: cast removes address space '__user' of expression.
> 
> Since the valid_user_address(x) macro implicitly casts the argument
> to long and compares the converted value of x to zero, casting ptr
> to unsigned long has no functional impact and does not trigger a 
> Sparse warning either.

Why does sparse complain about a cast to 'long' but not 'unsigned long'?
 Both remove the '__user' address space from the expression.  Were there
just so many __user pointers being cast to 'unsigned long' that there's
an exception in sparse for 'void __user *' => 'unsigned long'?

Either way, if we're going to fix it it seems like it would be better to
valid_user_address() actually handle, well, __user addresses rather than
expecting callers to do it.