RFR: 8224851: AArch64: fix warnings and errors with Clang and GCC 8.3

[Andrew Haley]

On 6/12/19 10:35 AM, Nick Gasson wrote:
> I also replaced the call to _get_previous_fp() in os::current_frame() with
> 
>    *(intptr_t **)__builtin_frame_address(0);
> 
> As it generates the same code and avoids the `register intptr_t **fp 
> __asm__ (SPELL_REG_FP);' declaration which clang doesn't support. Also 
> the following comment in _get_previous_fp seems to be wrong:
> 
>    // fp is for this frame (_get_previous_fp). We want the fp for the
>    // caller of os::current_frame*(), so go up two frames. However, for
>    // optimized builds, _get_previous_fp() will be inlined, so only go
>    // up 1 frame in that case.
>    #ifdef _NMT_NOINLINE_
>      return **(intptr_t***)fp;
>    #else
>      return *fp;
>    #endif

All of this seems horribly fragile. I'll have a look at what this is supposed
to be used for and think about a stable and robust way to do it.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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