Bsm refactor

[jdksjolen]

Hi,

This is the first commit in #23250 (hash 616f941 ) with some small changes.

Change to BootstrapMethods attribute storage

This refactoring changes how we store and access the BootstrapMethods attribute in the constant pool.

As a reminder, the BSMs attribute has the following format[0]:

BootstrapMethods_attribute {
    u2 attribute_name_index;
    u4 attribute_length;
    u2 num_bootstrap_methods;
    {   u2 bootstrap_method_ref;
        u2 num_bootstrap_arguments;
        u2 bootstrap_arguments[num_bootstrap_arguments];
    } bootstrap_methods[num_bootstrap_methods];
}

Note that each entry in the bootstraps_methods array may have a different size, as they may have a different num_bootstrap_arguments. That means that in order to access the nth element in the bootstraps_methods array you need to know at what byte offset that nth element starts. The way we can do that is to have a supplementary array consisting of u4s which indicate at which byte offset each entry starts. This PR changes where we store that array.

We used to have one single array, called operands, which stored both the offsets and BSM attribute together, one after the other. It looked a bit like this:

operands
     +-----------------------\+/
+--+-++--+--+--+-o-+----+----++---+-----+-----+-----+
|  |  |  |  |  |u2 |u2  | a0 | u2 | u2  | a0  | a1  |  ...
|  |  |offsets |  Entry #1   |   Entry #2           |
++-+--+--+--+--++--+----+----+----+-----+-----+-----+
 |             /|\
 |              |
 +--------------+

This PR splits them into two: _bsm_attribute_entries for storing the actual entries, and _bsm_attribute_offsets for storing the offsets of each entry into that array.

It looks like this:

offsets
+--+--+-------------------------+
|  |  |  ...                    |
++-+\-+-------------------------+
 |   |
\|/  ---------------\+/
++---+---+----+----+-+-+----+----+-----+------+
| u2 | u2|  a0| a1 | u2| u2 | a0 | a1  |   a2 |...
+----+---+----+----+---+----+---- -----+------+
entries

Add BootstrapMethodAttributeEntry

Instead of having many BSM attribute specific methods in the ConstantPool class, we introduce the BSMAE class and use that instead. You ask the constant pool for a particular BSMAE and you use that to get out the arguments, arg count, etc.

The other stuff

There's some other stuff in here, still figuring that out.

[0] https://docs.oracle.com/javase/specs/jvms/se24/html/jvms-4.html#jvms-4.7.23

---

Progress

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

Warnings

 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/BorderLayout-1.gif)
 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/FlowLayout-1.gif)
 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/GridBagLayout-1.gif)
 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/GridBagLayout-2.gif)
 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/GridLayout-1.gif)
 ⚠️ Patch contains a binary file (src/java.desktop/share/classes/java/awt/doc-files/GridLayout-2.gif)

Contributors

• John R Rose <[email protected]>

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/24878/head:pull/24878
$ git checkout pull/24878

Update a local copy of the PR:
$ git checkout pull/24878
$ git pull https://git.openjdk.org/jdk.git pull/24878/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 24878

View PR using the GUI difftool:
$ git pr show -t 24878

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/24878.diff

[bridgekeeper]

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[jdksjolen]

/contributor add rose00

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@jdksjolen rose00 was not found in the census.

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[jdksjolen]

/contributor add @rose00

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@jdksjolen
Contributor John R Rose <[email protected]> successfully added.

[jdksjolen]

This needs to be double checked.

[openjdk]

@jdksjolen this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout bsm-refactor
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push