Re: [Xen-devel] [PATCH] ARM: xen: unexport HYPERVISOR_platform_op function

[Julien Grall]

On 01/10/2019 15:33, Mark Rutland wrote:
> Hi Julien,

Hi Mark,

> On Sat, Sep 07, 2019 at 11:05:45AM +0100, Julien Grall wrote:
> > On 9/6/19 6:20 PM, Andrew Cooper wrote:
> > > On 06/09/2019 17:00, Arnd Bergmann wrote:
> > > > On Fri, Sep 6, 2019 at 5:55 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > > > > On 06/09/2019 16:39, Arnd Bergmann wrote:
> > > > > > HYPERVISOR_platform_op() is an inline function and should not
> > > > > > be exported. Since commit 15bfc2348d54 ("modpost: check for
> > > > > > static EXPORT_SYMBOL* functions"), this causes a warning:
> > > > > >
> > > > > > WARNING: "HYPERVISOR_platform_op" [vmlinux] is a static EXPORT_SYMBOL_GPL
> > > > > >
> > > > > > Remove the extraneous export.
> > > > > >
> > > > > > Fixes: 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL* functions")
> > > > > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > > > > Something is wonky.  That symbol is (/ really ought to be) in the
> > > > > hypercall page and most definitely not inline.
> > > > >
> > > > > Which tree is that changeset from?  I can't find the SHA.
> > > > This is from linux-next, I think from the kbuild tree.
> > >
> > > Thanks.
> > >
> > > Julien/Stefano: Why are any of these hypercalls out-of-line? ARM
> > > doesn't use the hypercall page, and there is no argument translation
> > > (not even in arm32 as there are no 5-argument hypercalls declared).
> >
> > I am not sure how the hypercall page makes things different. You still have
> > to store the arguments in the correct register so...
> >
> > > They'd surely be easier to implement with a few static inlines and some
> > > common code, than to try and replicate the x86 side hypercall_page
> > > interface ?
> >
> > ... I don't think they will be easier to implement with a few static
> > inlines. The implementation will likely end up to be similar to
> > arch/x86/asm/xen/hypercall.h.
> >
> > Furthermore, one of the downside of per-arch static inline is it is more
> > difficult to ensure the prototype match for all the architectures. Although,
> > it might be possible to make them common by only requesting per-arch to
> > implement HYPERCALL_N(...).
> >
> > So I think the code is better as it is.
> >
> > While looking at the code, I also realized that the implementation of
> > HYPERCALL_dm_op might be incorrect for Arm32. Similarly do privcmd call, I
> > think dm_op call should enable user access as they will be used by
> > userspace.
> >
> > We don't use dm_op on Arm so far, hence why I think this was unnoticed. I
> > will see if I can reproduce it and send a patch.
>
> I'm seeing this when building arm64 defconfig v5.4-rc1:
>
> | [mark@lakrids:~/src/linux]% usekorg 8.1.0  make ARCH=arm64 CROSS_COMPILE=aarch64-linux- -j56 -s
> | arch/arm64/Makefile:62: CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built
> | WARNING: "HYPERVISOR_platform_op" [vmlinux] is a static EXPORT_SYMBOL_GPL
> | WARNING: "HYPERVISOR_platform_op" [vmlinux] is a static EXPORT_SYMBOL_GPL
>
> I couldn't see a follow-up; do you have a patch for this?

The first e-mail of the thread should contain a patch to address the warning 
(see [1]). But it is still waiting on an Ack from Stefano so it can get merged.

Cheers,

[1] https://patchwork.kernel.org/patch/11135601/

--
Julien Grall