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

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On August 22, 2016 3:23:06 PM PDT, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>On Sun, Aug 21, 2016 at 10:52 AM, Linus Torvalds
><torvalds@linux-foundation.org> wrote:
>> On Sat, Aug 20, 2016 at 11:42 PM, Al Viro <viro@zeniv.linux.org.uk>
>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

The nice thing about using __builtin_ is that I believe gcc is aware of which registers need saving, and also know that the common path doesn't clobber registers at all.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.

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[PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-08-19 21:20 +0200
  Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-19 23:30 +0200
    Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-20 00:10 +0200
      Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-20 00:20 +0200
        Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-21 01:40 +0200
          Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-21 02:20 +0200
            Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-21 02:50 +0200
              Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-21 03:10 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault "H. Peter Anvin" <hpa@zytor.com> - 2016-08-21 03:10 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-21 03:50 +0200
              Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Jakub Jelinek <jakub@redhat.com> - 2016-08-21 07:00 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-21 08:50 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-21 20:00 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-23 00:30 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault "H. Peter Anvin" <hpa@zytor.com> - 2016-08-23 01:20 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Linus Torvalds <torvalds@linux-foundation.org> - 2016-08-23 01:50 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of  fault David Miller <davem@davemloft.net> - 2016-08-23 02:00 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault "H. Peter Anvin" <hpa@zytor.com> - 2016-08-23 02:10 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault "H. Peter Anvin" <hpa@zytor.com> - 2016-08-23 02:00 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault Al Viro <viro@ZenIV.linux.org.uk> - 2016-08-23 02:20 +0200
                Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault "H. Peter Anvin" <hpa@zytor.com> - 2016-08-23 01:20 +0200

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