RFR: 8364816: GetLastError() in os_windows.cpp should not store value to errno [v2]

[Joel Sikström]

On Wed, 27 Aug 2025 07:33:47 GMT, Anton Artemov <duke at openjdk.org> wrote:

>> src/hotspot/os/windows/os_windows.cpp line 4700:
>> 
>>> 4698:   if (hFile == INVALID_HANDLE_VALUE) {
>>> 4699:     DWORD errcode = ::GetLastError();
>>> 4700:     log_debug(os)("get_path_to_target() failed to CreateFileW: GetLastError->%lu.", errcode);
>> 
>> The callers of `get_path_to_target` expects errno to be set, which it isn't anymore. We should probably set errno in this case and update the comments.
>> 
>> See: https://github.com/openjdk/jdk/blob/master/src/hotspot/os/windows/os_windows.cpp#L4804-L4813 and https://github.com/openjdk/jdk/blob/master/src/hotspot/os/windows/os_windows.cpp#L5018-L5027
>
> Thanks for spotting. Actually, this comment, as well as the code around it, is mine as well. When writing it, I was storing results of `GetLastError()` in `errno`, which as we know is wrong and is addressed in this PR. 
> 
> The callers of `get_path_to_target()` do not expect any value in `errno` actually. The only thing they do when failing (this is where the `errno` value would be potentially useful) is that freeing some char array and returning -1. The error, which caused it, has been already reported. The comment is misleading. I fixed it.

I think we still need to set errno in the failure path in https://github.com/toxaart/jdk/blob/JDK-8364816-get-last-error/src/hotspot/os/windows/os_windows.cpp#L4804-L4811.

Right next to the Windows specific code that you removed in this PR, we are checking the errno result, which is unset if we exit from the path calling `get_path_to_target()`. See https://github.com/toxaart/jdk/blob/JDK-8364816-get-last-error/src/hotspot/share/cds/aotClassLocation.cpp#L234-L246.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26901#discussion_r2303285732