[jdk17] RFR: 8268717: Upstream: 8268673: Stack walk across optimized entry frame on fresh native thread fails [v2]

[Jorn Vernee]

On Thu, 17 Jun 2021 00:23:19 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add comment about optimized entry frames only being generated on x86_64
>
> src/hotspot/share/runtime/frame.inline.hpp line 54:
> 
>> 52: inline bool frame::is_first_frame() const {
>> 53:   return (is_entry_frame() && entry_frame_is_first())
>> 54:       || (is_optimized_entry_frame() && optimized_entry_frame_is_first());
> 
> Given `optimized_entry_frame_is_first` is only defined on a couple of platforms, it is far from obvious that this call can never happen on the other platforms. A comment explaining this would be useful.

Thanks, I've added the following comment:

```C++
inline bool frame::is_first_frame() const {
  return (is_entry_frame() && entry_frame_is_first())
      // optimized_entry_frame_is_first is currently only implemented on x86_64.
      // This is okay since optimized entry frames are only generated on x86_64
      // as well (see ProgrammableUpcallHandler::generate_optimized_upcall_stub
      // in universalUpcallHandler_x86_64.cpp), so is_optimized_entry_frame will
      // always return false on platforms where optimized_entry_frame_is_first
      // is not implemented.
      || (is_optimized_entry_frame() && optimized_entry_frame_is_first());
}

-------------

PR: https://git.openjdk.java.net/jdk17/pull/76