8374521: Support fine-grained native debug levels #29056

shipilev · 2026-01-06T08:28:35Z

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 :)

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Issue

JDK-8374521: Support fine-grained native debug levels (Enhancement - P4)

Reviewers

Erik Joelsson (@erikj79 - Reviewer)
Kerem Kat (@krk - Author)
Christoph Langer (@RealCLanger - Reviewer)

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$ git checkout pull/29056

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/29056/head

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bridgekeeper · 2026-01-06T08:29:43Z

👋 Welcome back shade! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2026-01-06T08:31:33Z

@shipilev This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8374521: Support fine-grained native debug levels

Reviewed-by: erikj, krk, clanger

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 18 new commits pushed to the master branch:

6b3c1e0: 8373833: "error.cert.not.found" and "error.explicit-sign-no-cert" errors duplicate each other
7c979c1: 8374308: ImageBufferCache has no effect and can be removed
53300b4: 8373830: Refactor test/jdk/java/time/test tests to use JUnit over TestNG
... and 15 more: https://git.openjdk.org/jdk/compare/2fbc4162e808f14b6114499f49db3e6ef1590f24...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

openjdk · 2026-01-06T08:32:31Z

@shipilev The following label will be automatically applied to this pull request:

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When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

shipilev · 2026-01-06T08:43:02Z

Motivational improvements in debug info sizes:

$ ls -sh ./build/linux-x86_64-server-fastdebug/images/jdk/lib/server/libjvm.debuginfo
# level=1: 144M
# level=2: 860M
# level=3: 892M

Since debuginfo-s are duplicated several times in our build dir, we are scratching against the 14G guaranteed free space on GHA runners, and reducing to level=1 buys us a lot of headroom:

$ du -sh build/linux-x86_64-server-fastdebug/
# level=1:  4.0G
# level=2: 14.0G
# level=3: 16.0G

shipilev · 2026-01-06T12:15:02Z

Similar thing on MacOS AArch64 (Clang):

% du -sh ./build/macosx-aarch64-server-fastdebug/images/jdk/lib/server/libjvm.dylib.dSYM/ 
# level=1:  92M
# level=2: 202M
# level=3: 202M

% du -sh ./build/macosx-aarch64-server-fastdebug/     
# level=1: 3.6G
# level=2: 5.6G
# level=3: 5.6G

mlbridge · 2026-01-06T13:21:20Z

Webrevs

krk · 2026-01-06T13:58:57Z

make/autoconf/flags-cflags.m4

  # Debug prefix mapping if supported by compiler
  DEBUG_PREFIX_CFLAGS=

+  UTIL_ARG_WITH(NAME: fine-debug-level, TYPE: string,


How about debug-info-level?

I think I agree with this naming suggestion.

--with-debug-info-level it is!

erikj79

I think this is a good idea.

erikj79 · 2026-01-06T14:20:14Z

make/autoconf/flags-cflags.m4

  # Debug prefix mapping if supported by compiler
  DEBUG_PREFIX_CFLAGS=

+  UTIL_ARG_WITH(NAME: fine-debug-level, TYPE: string,


I think I agree with this naming suggestion.

erikj79 · 2026-01-06T14:20:43Z

make/autoconf/flags-cflags.m4

+  UTIL_ARG_WITH(NAME: fine-debug-level, TYPE: string,
+    DEFAULT: 2,
+    RESULT: FINE_DEBUG_LEVEL,
+    DESC: [Sets the fine-tuned debug level, when debug info generation is enabled],


I think we should clarify that this only applies to GCC and Clang.

I added the blurb into description.

shipilev · 2026-01-06T15:56:33Z

A few more touchups: moved the block to handle both compilers at the same time, stopped issuing -g2 when default -g would do, started to fail when compiler rejects the debug info level requested.

RealCLanger

Looks like a nice resource usage improvement

shipilev · 2026-01-07T06:56:07Z

Thanks for reviews! I am thinking to align the option name with current --with-native-debug-symbols better, since it is really about those. How about this?

  --with-native-debug-symbols-level
                          set the native debug symbols level (GCC and Clang only) [toolchain default]
  --with-native-debug-symbols
                          set the native debug symbol configuration (none,
                          internal, external, zipped) [varying]

RealCLanger · 2026-01-07T07:57:09Z

OK, yes, that sounds like a good suggestion.

erikj79 · 2026-01-07T14:30:04Z

Thanks for reviews! I am thinking to align the option name with current --with-native-debug-symbols better, since it is really about those. How about this?

Yes, that looks even better.

shipilev · 2026-01-07T18:07:58Z

Thanks! Here goes.

/integrate

openjdk · 2026-01-07T18:10:08Z

Going to push as commit dd20e91.
Since your change was applied there have been 30 commits pushed to the master branch:

640343f: 8373724: Assertion failure in TestSignumVector.java with UseAPX
3541bc8: 8373538: Migrate all tests to null-safe "SimpleSSLContext" methods
da14813: 8373453: C2 SuperWord: must handle load slices that have loads with different memory inputs
... and 27 more: https://git.openjdk.org/jdk/compare/2fbc4162e808f14b6114499f49db3e6ef1590f24...master

Your commit was automatically rebased without conflicts.

openjdk · 2026-01-07T18:10:16Z

@shipilev Pushed as commit dd20e91.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

RealCLanger · 2026-01-07T21:07:41Z

Thanks! Here goes.

/integrate

OK, no --with-native-debug-symbols-level then?

shipilev · 2026-01-07T22:07:42Z

Thanks! Here goes.
/integrate

OK, no --with-native-debug-symbols-level then?

Dang. I have not pushed my local commit! Argh. I'll follow up with the update tomorrow.

shipilev · 2026-01-08T08:07:35Z

Dang. I have not pushed my local commit! Argh. I'll follow up with the update tomorrow.

#29108

shipilev added 2 commits January 6, 2026 09:16

Debug levels

df1c997

Also enable in GHA

ea09da2

openjdk bot added the build build-dev@openjdk.org label Jan 6, 2026

shipilev mentioned this pull request Jan 6, 2026

8374507: GHA: Limit debug symbols generation to conserve disk space #29030

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5 tasks

Fallback when compiler does not support the value

ebca865

shipilev marked this pull request as ready for review January 6, 2026 13:15

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krk reviewed Jan 6, 2026

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erikj79 reviewed Jan 6, 2026

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shipilev added 2 commits January 6, 2026 16:40

--with-debug-info-level

4971365

Default to default, common the block, fail on incorrect debug level

6365bb9

erikj79 approved these changes Jan 6, 2026

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krk approved these changes Jan 6, 2026

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8374521: Support fine-grained native debug levels #29056

8374521: Support fine-grained native debug levels #29056

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