Re: [PATCH v6 1/3] xen/arm: add support for run_in_exception_handler()

[Jürgen Groß <jgross@xxxxxxxx>]

On 20.01.21 19:20, Julien Grall wrote:
> Hi Juergen,
>
> On 16/01/2021 10:33, Juergen Gross wrote:
> > Add support to run a function in an exception handler for Arm. Do it
> > as on x86 via a bug_frame, but pass the function pointer via a
> > register (this needs to be done that way, because inline asm support
> > for 32-bit Arm lacks the needed functionality to reference an
> > arbitrary function via the bugframe).
> I was going to commit the series, but then realized the commit message 
> and comment needs some tweaking because technically GCC is supporting 
> 'i' (I managed to get it working with -fno-pie).
> So how about:
>
> "This is needed to be done that way because GCC complains about invalid 
> constraint when using a function pointer with "i" and PIE is enabled 
> (default on most of GCC shipped with distro). Clang happily accepts it, 
> so it may be a bug in GCC."
>
> > +/*
> > + * Unfortunately gcc for arm 32-bit doesn't support the "i" 
> > constraint, so
> > + * the easiest way to implement run_in_exception_handler() is to pass 
> > the
> > + * to be called function in a fixed register.
> > + */
> This comment should also be updated.
>
> I can update both while committing if you are happy with the change.
Fine with me.

Thanks,


Juergen

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