2006-12-12 01:23:26

by Jeremy Fitzhardinge

Subject: Why disable vdso by default with CONFIG_PARAVIRT?

Hi Andi,

What problem do they cause together? There's certainly no problem with
Xen+vdso (in fact, its actually very useful so that it picks up the
right libc with Xen-friendly TLS).

J

2006-12-12 01:42:24

by Zachary Amsden

Subject: Re: Why disable vdso by default with CONFIG_PARAVIRT?

Jeremy Fitzhardinge wrote:
> Hi Andi,
>
> What problem do they cause together? There's certainly no problem with
> Xen+vdso (in fact, its actually very useful so that it picks up the
> right libc with Xen-friendly TLS).
>

Methinks the compat VDSO support got broken in the config? Paravirt +
COMPAT_VDSO are incompatible.

2006-12-12 01:45:07

by Jeremy Fitzhardinge

Subject: Re: Why disable vdso by default with CONFIG_PARAVIRT?

Zachary Amsden wrote:
> Jeremy Fitzhardinge wrote:
>> Hi Andi,
>>
>> What problem do they cause together? There's certainly no problem with
>> Xen+vdso (in fact, its actually very useful so that it picks up the
>> right libc with Xen-friendly TLS).
>>
>
> Methinks the compat VDSO support got broken in the config? Paravirt +
> COMPAT_VDSO are incompatible.

Yes, that's true, but I'm looking at arch/i386/kernel/sysenter.c:

#ifdef CONFIG_PARAVIRT
unsigned int __read_mostly vdso_enabled = 0;
#else
unsigned int __read_mostly vdso_enabled = 1;
#endif

I can't think of any reason why that should be necessary.

J

2006-12-12 01:46:45

by Zachary Amsden

Subject: Re: Why disable vdso by default with CONFIG_PARAVIRT?

Jeremy Fitzhardinge wrote:
> Zachary Amsden wrote:
>
>> Jeremy Fitzhardinge wrote:
>>
>>> Hi Andi,
>>>
>>> What problem do they cause together? There's certainly no problem with
>>> Xen+vdso (in fact, its actually very useful so that it picks up the
>>> right libc with Xen-friendly TLS).
>>>
>>>
>> Methinks the compat VDSO support got broken in the config? Paravirt +
>> COMPAT_VDSO are incompatible.
>>
>
> Yes, that's true, but I'm looking at arch/i386/kernel/sysenter.c:
>
> #ifdef CONFIG_PARAVIRT
> unsigned int __read_mostly vdso_enabled = 0;
> #else
> unsigned int __read_mostly vdso_enabled = 1;
> #endif
>
> I can't think of any reason why that should be necessary.
>

It's not for us or Xen. Perhaps it came from lhype?

2006-12-12 01:50:09

by Jeremy Fitzhardinge

Subject: Re: Why disable vdso by default with CONFIG_PARAVIRT?

Zachary Amsden wrote:
> It's not for us or Xen. Perhaps it came from lhype?

(I suspect it came from Andi's fevered brain.) If lhype can't deal with
vdso, it can turn it off for itself - but I don't think its a problem
for lhype.

J