Re: [PATCH v2] x86: Remove compat vdso support

H. Peter Anvin
2014-03-11T16:22:53Z

On 03/11/2014 08:30 AM, Linus Torvalds wrote:
> On Tue, Mar 11, 2014 at 7:53 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>>
>> I wonder if we can actually detect buggy glibc versions at runtime.
>
> No, don't do that. That way lies madness.
>
> What might be acceptable then is to just keep the old config name, and
> if the COMPAT_VDSO config is enabled, you just disable the non-compat
> vdso. At least that way, presumably any opensuse people would have
> their kernel config continue working.
>
> Then if people have that enabled but didn't need it, you can enable
> it at runtime with
>
> echo 1 > /proc/sys/abi/vsyscall32
>
> which presumably would need to be exposed on 32-bit kernels too (it
> looks like a x86-64-only thing right now)
>
> The important thing is that we do *not* break user space. Not ever.
> Not knowingly.
>

As much as I wouldn't mind getting rid of the compat vdso, I really
don't understand why the trivial solution is being ruled out -- the
trivial solution being to just reserve a little more space in the fixmap
area.

I know Andy wants to move the vdso into a normal vma, which I certainly
support, but it is definitely the non-compat case.

-hpa