Re: [PATCH v4 1/3] xen/arm: add support for run_in_exception_handler()

[Jürgen Groß <jgross@xxxxxxxx>]

On 14.12.20 10:03, Jan Beulich wrote:
> On 14.12.2020 08:56, Juergen Gross wrote:
> > Add support to run a function in an exception handler for Arm. Do it
> > the same way as on x86 via a bug_frame.
> >
> > Unfortunately inline assembly on Arm seems to be less capable than on
> > x86, leading to functions called via run_in_exception_handler() having
> > to be globally visible.
> Could you extend on this? I don't understand what the relevant
> difference is, from just looking at the changes.
The problem seems to be that a static symbol referenced from the inline
asm seems not to silence the error that this static symbol isn't being
used. On x86 the bug_frame is constructed using the %c modifier, which
is not supported for Arm (at least gcc 7 used in my compile test
complained), but seems to be enough for gcc on x86 to not complain.

> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > V4:
> > - new patch
> >
> > I have verified the created bugframe is correct by inspecting the
> > created binary.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   xen/arch/arm/traps.c       | 10 +++++++++-
> >   xen/drivers/char/ns16550.c |  3 ++-
> >   xen/include/asm-arm/bug.h  | 32 +++++++++++++++++++++-----------
> >   3 files changed, 32 insertions(+), 13 deletions(-)
> Aiui you also need to modify xen.lds.S to cover the new (or really
> the last renamed) section.
Oh, right. I thought of that before, but forgot again. Thanks for the
reminder.


Juergen

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