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8261578: jextract crashes with Crossing storage unit boundaries #451



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@mcimadamore mcimadamore commented Feb 15, 2021

This patch overhauls the logic for bitfield detection, after discovering a number of related failures. The current logic attempts to find a unique container size for a bunch of adjacent bitfields (either 8, 16, 32 or 64 bits) and then allocates the bitfields into subsequent containers of same size.

The fact that the container size is decided once and for all at the beginning of parsing of the bitfield sequence is problematic, and breaks down in cases where containers are used only partially, or where padding is inserted.

To overcome these issues, I've now switched to a more flexible algorithm which, instead of fixing a container size before hands, just emits a new container whenever the cumulative offset of adjacent bitfield has reached a word boundary (either 8, 16, 32, 64 bits).

This makes the algorithm less strict, and less prone to crashes. However, since we're still reverse engineering bitfield information (as libclang doesn't give us that information), the solution will probably require more tweaks, especially in order to support packed structures, in which compilers emit bitfields which happily span across a word boundary.

For this reason, I did not included some of the examples listed in JDK-8261578 which make use of the packed attribute/pragma - that is unsupported anyway, see JDK-8259832. We should come back to these examples when support for pragma is added (for now I've added a link from the pragma JBS issue to this one, so that we'll not forget).

As for testing, I followed what other tests in this area did in the past - but I believe at some point we probably need to write better tests which use the jextract API to query bitfield offsets and sizes, because the tests, as currently written, do not assert much, other than that jextract is not failing badly.


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  • JDK-8261578: jextract crashes with Crossing storage unit boundaries



$ git fetch pull/451/head:pull/451
$ git checkout pull/451

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@bridgekeeper bridgekeeper bot commented Feb 15, 2021

👋 Welcome back mcimadamore! A progress list of the required criteria for merging this PR into foreign-jextract 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 label Feb 15, 2021
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@openjdk openjdk bot commented Feb 15, 2021

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

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

8261578: jextract crashes with Crossing storage unit boundaries

Reviewed-by: sundar

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@openjdk openjdk bot added the ready label Feb 15, 2021
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@mcimadamore mcimadamore commented Feb 15, 2021


@openjdk openjdk bot closed this Feb 15, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Feb 15, 2021
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@openjdk openjdk bot commented Feb 15, 2021

@mcimadamore Pushed as commit 4d7180a.

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