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

[Andrew Haley]

Hi,

On 6/12/19 10:35 AM, Nick Gasson wrote:

> Sorry for the delay, I've put an updated webrev here:
> 
> http://cr.openjdk.java.net/~ngasson/8224851/webrev.1/
> 
> Changes since the last patch:
> 
> * Replaced ~((1<<12) - 1) with -1u<<12
> 
> * Use __atomic_add_fetch in Atomic::PlatformAdd #ifdef __clang__
> 
> * Use __builtin_frame_address(0) in os::current_frame()
> 
> * Use placement new / copy assignment in pf()
> 
> 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
> 
> Even on -O0 gcc won't generate a stack frame for this function so if 
> _NMT_NOINLINE_ is defined you get the caller's caller's FP rather than 
> the caller's FP. I just deleted the function as it's not used anywhere else.
> 
> BTW we can't use __builtin_frame_address(1) as GCC gives a warning when 
> this is called with a non-zero argument (-Wframe-address).
> 
> Tested jtreg hotspot_all_no_apps and jdk_core (gcc 7.3).

OK, that's all good. Thanks.

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