[lworld] RFR: 8371993: [lworld] Aarch64: save bad values instead of rfp and lr above the extension space [v2]

[Marc Chevalier]

On Fri, 28 Nov 2025 11:59:34 GMT, Manuel Hässig <mhaessig at openjdk.org> wrote:

>> Marc Chevalier has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review
>
> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 5915:
> 
>> 5913: #ifdef ASSERT
>> 5914:     }
>> 5915: #endif
> 
> Not sure if this is a good idea, but you could omit the braces on the else to make this a bit less busy.

I agree it's busy, but I like explicit braces, rust-style. Especially with `#ifdef` in the middle, it looks easy to do something wrong with un-braced blocks. I'm not so shocked by the current style but another option I see would be

if (DEBUG_ONLY(save_fake_rfp_lr) NOT_DEBUG(false)) {
  mov_immediate64(rscratch1, ((uint64_t)badRegWordVal) << 32 | (uint64_t)badRegWordVal);
  stp(rscratch1, rscratch1, Address(sp, framesize - 2 * wordSize));
} else {
  stp(rfp, lr, Address(sp, framesize - 2 * wordSize));
}

I am very confident gcc will remove the branch entirely in non-debug.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1764#discussion_r2571484688