RFR: 8374521: Support fine-grained native debug levels

[Erik Joelsson]

On Tue, 6 Jan 2026 13:58:57 GMT, Kerem Kat <krk at openjdk.org> wrote:

>> [JDK-8374507](https://bugs.openjdk.org/browse/JDK-8374507) forced me to look into debug info sizes again. And I remembered that GCC actually have debug-level support, which can select what kind of diagnostic data is in the debug info. See: https://gcc.gnu.org/onlinedocs/gcc-4.5.0/gcc/Debugging-Options.html
>> 
>> Allowing users to configure the debug level allows two major deviations from the default level (2):
>>  level=1: significantly reduce the debug info size, but still allow backtrace reconstruction
>>  level=3: add even more debugging info, like macro expansion, into the debug data
>> 
>> This RFE upstreams the variant the patch that I have been using in builds.shipilev.net binaries: the fastdebug variants there are done with GCC level=1, greatly optimizing the debug binary sizes, while still maintaining the major benefit of debug binaries -- rich crash diagnostics.
>> 
>> I threw in this option into current GHA builds to conserve more disk space on runners and/or transfers. 
>> 
>> I am open for bikeshedding on the option name :)
>
> make/autoconf/flags-cflags.m4 line 72:
> 
>> 70:   DEBUG_PREFIX_CFLAGS=
>> 71: 
>> 72:   UTIL_ARG_WITH(NAME: fine-debug-level, TYPE: string,
> 
> How about `debug-info-level`?

I think I agree with this naming suggestion.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/29056#discussion_r2665084455