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

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.



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