linux-kernel - Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

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Date:	Tue, 18 Dec 2012 17:52:38 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, ak@...ux.intel.com, aarcange@...hat.com,
	john.stultz@...aro.org, luto@...capital.net, xemul@...allels.com,
	gorcunov@...nvz.org, andriy.shevchenko@...ux.intel.com
Subject: Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

Am Dienstag, den 18.12.2012, 08:17 -0800 schrieb H. Peter Anvin:
> On 12/18/2012 01:40 AM, stefani@...bold.net wrote:
> > From: Stefani Seibold <stefani@...bold.net>
> > 
> > This patch adds support for 32 bit VDSO.
> > 
> > For 32 bit programs running on a 32 bit kernel, the same mechanism is
> > used as for 64 bit programs running on a 64 bit kernel.
> > 
> > For 32 bit programs running under a 64 bit IA32_EMULATION, it is a
> > little bit more tricky. In this case the VVAR and HPET will be mapped
> > into the 32 bit address space, by cutting of the upper 32 bit. So the
> > address for this will not changed in the view of the 32 bit VDSO. The
> > HPET will be mapped in this case at 0xff5fe000 and the VVAR at 0xff5ff000.
> > 
> > The transformation between the in 64 bit kernel representation and the 32 bit
> > abi will be also provided.
> > 
> > So we have one VDSO Source for all.
> > 
> 
> You seem to once again have disregarded the request to make the vvar and
> hpet part of the vdso address space proper.  If this is not possible or
> highly impractical, please extend a technical motivation why that is so,
> rather than simply ignoring it.
> 

Pardon, i never disregarded nor i have agreed that this is going to be a
part of the VDSO. I currently have also no idea how to do this and i see
no need at the moment to do this revamp. The 64 bit VDSO lives since
more than 6 years with this kind of implementation.

You asked me to do the VDSO 32 bit stuff for the IA32_EMULATION, before
it is ready for inclusion into the kernel. Thats exactly what i did. I
spend the whole weekend of my spare time to do this implementation. Now
we have them all.

The patch works perfectly, all issues are solved:

- Calling conventions
- ABI transformations
- System call gateway for X86 32 bit
- Mapping of the FIXMAP and HPET into the lower 32 bit address space for
IA32_EMULATION
- Support for 32 bit programs in 32 kernel and 64 bit kernel
- One VDSO source for all

If you prefer an other solutions, its okay. There are many ways to code
things. But for now i think it is a good step ahead. That is what i
currently can provide.

- Stefani


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