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8316859: RISC-V: Disable detection of V through HWCAP #15898

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@luhenry luhenry commented Sep 25, 2023

Some dev boards only support RVV version 0.7, while the OpenJDK only supports RVV version 1.0. These two versions are not compatible with each other. Given the V bit is set through HWCAP on some custom kernels, regardless of the version, it can lead to generating V instructions on boards that don't support RVV version 1.0 (ex: Sipeed LicheePi), leading to a SIGILL.

That is an acceptable workaround as only Linux Kernel v6.5+ supports V, and that version already support hwprobe anyway


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  • JDK-8316859: RISC-V: Disable detection of V through HWCAP (Task - P4)

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👋 Welcome back luhenry! 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 openjdk bot added the rfr Pull request is ready for review label Sep 25, 2023
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@luhenry The following label will be automatically applied to this pull request:

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V should be disabled in vcsr pre-6.5. Even if you manage somehow to enabled it you still need all registers saved and restored on a context switch, i.e. kernel must be aware of a user space program using V.

As you say, an aware kernel also supports hw probe, sensible, thanks!

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

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8316859: RISC-V: Disable detection of V through HWCAP

Reviewed-by: rehn, fyang

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luhenry commented Sep 25, 2023

/integrate

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openjdk bot commented Sep 25, 2023

Going to push as commit 311c746.
Since your change was applied there have been 198 commits pushed to the master branch:

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@luhenry Pushed as commit 311c746.

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luhenry commented Sep 25, 2023

/backport jdk21u

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@luhenry the backport was successfully created on the branch luhenry-backport-311c7461 in my personal fork of openjdk/jdk21u. To create a pull request with this backport targeting openjdk/jdk21u:master, just click the following link:

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This pull request contains a backport of commit 311c7461 from the openjdk/jdk repository.

The commit being backported was authored by Ludovic Henry on 25 Sep 2023 and was reviewed by Robbin Ehn and Fei Yang.

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If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk21u:

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sxa commented Sep 25, 2023

I've built this patch on top of jdk-21+35 and can confirm that it stops the SIGILL on my LicheePi 4A :-)

@luhenry luhenry deleted the dev/ludovic/hwcap-disable-v branch September 25, 2023 19:25
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