RFR: 8300197: Freeze/thaw an interpreter frame using a single copy_to_chunk() call

[Andrew Haley]

On Fri, 14 Apr 2023 13:45:12 GMT, Fredrik Bredberg <duke at openjdk.org> wrote:

> On certain architectures (like AARCH64) padding may be inserted between the locals and the rest of the stack frame in order to keep the frame pointer 16-byte-aligned.
> 
> This padding is currently not freezed, instead freezing of a single interpreter stack frame is done using two separate copy_to_chunk() calls (see recurse_freeze_interpreted_frame). Likewise, thawing is done using two separate copy_from_chunk() calls.
> 
> This poses a bit of a problem when trying to relativize stack addresses in interpreter frames ([JDK-8289296](https://bugs.openjdk.org/browse/JDK-8289296)). Since relative offsets may need to be changed during freezing and thawing.
> 
> By both freezing and thawing the padding we remove the need to change any relative offsets in runtime.
> 
> Tested tier1-tier8 on supported platforms, found no new issues. PowerPC and RISC-V was sanity tested using Qemu.

src/hotspot/cpu/aarch64/continuationFreezeThaw_aarch64.inline.hpp line 149:

> 147:   // on AARCH64, we may insert padding between the locals and the rest of the frame
> 148:   // (see TemplateInterpreterGenerator::generate_normal_entry, and AbstractInterpreter::layout_activation)
> 149:   // since we freeze the padding word (see recurse_freeze_interpreted_frame) in order to keep the same relativized

Suggestion:

  // because we freeze the padding word (see recurse_freeze_interpreted_frame) in order to keep the same relativized

... for clarity.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13477#discussion_r1169926915