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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.01.2021 19:20, Julien Grall wrote:
> 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."

May I ask why you think it's a bug in gcc? I'd rather consider it
a bug in clang. Taking the address of a symbol doesn't yield a
constant in PIC or PIE code, aiui.

Jan