Re: [RFC -tip 0/4] x86: reduce fixup of uaccess

H. Peter Anvin
2009-01-07T09:34:15Z

Hiroshi Shimamoto wrote:
> This is my second try to reduce fixup code size for exceptions of uaccess.
>
> This patch series reduces fixup code for exceptions of uaccess in signal.
>
> I gave up to make direct jump to end of function when an exception occurs.
> However, I thought fixup code could be reduced. The concept is that to add
> uaccess_err in thread_info and set it to -EFAULT on exception, finally check
> this value on the last of function.
>
> Is this good to reduce code size?
>

Hello Hiroshi,

The patches look technically really nice. I have a couple of stylistic
comments, though, which I'd like yours and others' comments on.

This introduces a new blocking construct, and it's not immediately
obvious in the source code. I think introducing a technically redundant
set of braces and dropping the parens from the try construct and the
redundant pointer might look better:

get_user_try {
/* do stuff */
} get_user_catch(err);

This makes it, in my opinion, much clearer that it is a new bracing
construct, and it also eliminates the need to form a pointer to "err"
(even though the compiler doesn't actually do so, it looks like it does
to the programmer.)

Also, I don't think we need double underscores for the wrapping
construct, since the get_user/__get_user (check/nocheck) etc.
distinction doesn't directly apply there.

What do you think?

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.