Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault

[H. Peter Anvin]

On August 22, 2016 3:23:06 PM PDT, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>On Sun, Aug 21, 2016 at 10:52 AM, Linus Torvalds
><torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Sat, Aug 20, 2016 at 11:42 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>wrote:
>>>
>>> It's not exactly setjmp/longjmp; what I had in mind was along the
>lines of
>>
>> That ends up having all the exact same issues as setjmp, and
>generally
>> you *do* want the compiler to know about it.
>
>So just in case you wanted to play around with it, here's a kernel
>implementation of 'setjmp/longjmp' for x86.
>
>It's very lightly tested (and I'll admit to editing it for some
>cleanups after that light testing), but it does look largely sane.
>
>The whole interface choice may be debatable: maybe it would be better
>to allocate the register buffer on the stack, and just hide a pointer
>to it in the task struct. Things like that could be changed fairly
>easily. But if you want to play around with this, this patch should
>get you started.
>
>Of course, you'd want to wrap things up somehow, and I would *not*
>want to see naked setjmp() calls in the kernel.
>
>And we'd need this for all other architectures too, but it's usually
>not hard to do. It needs to save all the callee-saved registers and
>the stack pointer and return address. That should generally be it.
>
>The 32-bit version has not been tested at all, but it compiled at some
>point, and the code looks mostly sane. The 64-bit code I actually had
>a stupid non-user-access test-case for.
>
>                Linus

How about the gcc native __builtin_setjmp stuff which is supposedly better?
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