8383990: Remove exception code filters from Windows AArch64 safefetch handler

[swesonga]

JDK-8383541: Safefetch should return the error value when accessing pages protected with PAGE_GUARD on windows-aarch64 added a handler for guard pages specifically. However, @mo-beck has pointed out that we can actually remove the list of exceptions altogether to future-proof the safefetch implementation since it uses a LDR instruction whose PC is known and checked for by handle_safefetch. The gtests added in JDK-8383541 still pass with this change.

---

• I confirm that I make this contribution in accordance with the OpenJDK Interim AI Policy.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed (2 reviews required, with at least 1 Reviewer, 1 Author)

Issue

• JDK-8383990: Remove exception code filters from Windows AArch64 safefetch handler (Bug - P4)

Reviewers

• Monica Beckwith (@mo-beck - Author) Review applies to adec8405
• David Holmes (@dholmes-ora - Reviewer)
• Julian Waters (@TheShermanTanker - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/31158/head:pull/31158
$ git checkout pull/31158

Update a local copy of the PR:
$ git checkout pull/31158
$ git pull https://git.openjdk.org/jdk.git pull/31158/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 31158

View PR using the GUI difftool:
$ git pr show -t 31158

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/31158.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back swesonga! 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]

@swesonga 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:

8383990: Remove exception code filters from Windows AArch64 safefetch handler

Reviewed-by: dholmes, jwaters, mbeckwit

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 49 new commits pushed to the master branch:

• 061bd07: 8379044: [macos] javadoc for setOpenURIHandler refers to wrong type
• 9f95d61: 8384428: C2: compiler/vectorapi/TestVectorLongToMaskNodeIdealization.java fails with AVX2
• 7264302: 8380446: C2: mask_and_replace_shift_amount should work for effectively-constant shift counts
• ... and 46 more: https://git.openjdk.org/jdk/compare/93a3d4aa76d1659185cf0f0eb9f05e3796b25692...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@dholmes-ora, @TheShermanTanker) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[openjdk]

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

• hotspot-runtime

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.

[openjdk]

The total number of required reviews for this PR has been set to 2 based on the presence of this label: hotspot-runtime. This can be overridden with the /reviewers command.

[mlbridge]

Webrevs

• 01: Full - Incremental (53870312)
• 00: Full (adec8405)

[mo-beck]

LGTM. Thanks.

[dholmes-ora]

It looks like exception_code is now unused and so can be removed from the signature.

Also this code has a section for _LP64 but as far as I can see the only call to handle_safefetch is from a section for _M_ARM64 - so the LP64 code seems dead as well.

[swesonga]

It looks like exception_code is now unused and so can be removed from the signature.

handle_safefetch (defined in src/hotspot/share/runtime/safefetch_static.hpp) is a function used by the other platforms as well. I left it unchanged to avoid special-casing it for windows-aarch64

Also this code has a section for _LP64 but as far as I can see the only call to handle_safefetch is from a section for _M_ARM64 - so the LP64 code seems dead as well.

_LP64 is defined for all 64-bit CPUs in make/autoconf/flags-cflags.m4 so that code is not dead. It is tested by the SafeFetchN_with_page_guard_protection gtest

[TheShermanTanker]

Looks good!

[dholmes-ora]

It looks like exception_code is now unused and so can be removed from the signature.

handle_safefetch (defined in src/hotspot/share/runtime/safefetch_static.hpp) is a function used by the other platforms as well. I left it unchanged to avoid special-casing it for windows-aarch64

Hmmm okay. It is declared in a shared header file but as far as I can see there are no callers from shared code. It seems to exist in the shared file to simplify the include process even though it is only used by platform-specific code and so could be declared in a platform specific header.

Also this code has a section for _LP64 but as far as I can see the only call to handle_safefetch is from a section for _M_ARM64 - so the LP64 code seems dead as well.

_LP64 is defined for all 64-bit CPUs

Doh! Sorry yes my brain read that referring to x86_64.

[dholmes-ora]

Looks good. Thanks

[swesonga]

/integrate

[openjdk]

@swesonga
Your change (at version 5387031) is now ready to be sponsored by a Committer.

[macarte]

/sponsor

[openjdk]

Going to push as commit f66380e.
Since your change was applied there have been 50 commits pushed to the master branch:

• 35913b8: 8384602: Remove AppContext from java.awt.Component
• 061bd07: 8379044: [macos] javadoc for setOpenURIHandler refers to wrong type
• 9f95d61: 8384428: C2: compiler/vectorapi/TestVectorLongToMaskNodeIdealization.java fails with AVX2
• ... and 47 more: https://git.openjdk.org/jdk/compare/93a3d4aa76d1659185cf0f0eb9f05e3796b25692...master

Your commit was automatically rebased without conflicts.

[openjdk]

@macarte @swesonga Pushed as commit f66380e.

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