Re: [Xen-devel] [PATCH ARM v8 3/4] mini-os: arm: build system

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-11-17 at 11:42 +0000, Thomas Leonard wrote:
> On 26 October 2014 10:25, Thomas Leonard <talex5@xxxxxxxxx> wrote:
> > On 26 October 2014 09:55, Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> 
> > wrote:
> >> Thomas Leonard, le Sun 26 Oct 2014 09:46:09 +0000, a Ãcrit :
> >>> Could you say a bit more about the linker problems you had?
> >>
> >> Really digging in the archives this time :)
> >>
> >> ia64-specific:
> >> http://lists.xen.org/archives/html/xen-ia64-devel/2008-03/msg00126.html
> >> http://lists.xen.org/archives/html/xen-ia64-devel/2008-12/msg00070.html
> >> x86_64-specific (missing red zone support)
> >> http://lists.xen.org/archives/html/xen-ia64-devel/2008-02/msg00251.html
> >>
> >> So I guess it could be OK on arm, but you have to make sure that Mini-OS
> >> implements the whole ABI that gcc will use. Testing is not enough, I got
> >> hit by the red zone for instance.
> >
> > On ARM, we have a separate stack for the IRQ handler, so the red zone
> > at least shouldn't be a problem.
> 
> Incidentally, why doesn't Mini-OS/x86 use a red zone? I assume there's
> a worthwhile performance benefit to it, and it would prevent subtle
> bugs when software is accidentally compiled for the normal ABI.

Redzones are incompatible with taking interrupts at the same privilege
level (which implies no stack switch, hence clobbering), and mini-os
runs everything at kernel privilege level.

Ian.


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