RFR: 8308031: Linkers should reject unpromoted variadic parameters [v3]

[Maurizio Cimadamore]

On Thu, 1 Jun 2023 15:16:42 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> In C, arguments smaller than `int` are promoted to (`unsigned`) `int`, and `float` is promoted to `double`, when being passed as variadic argument (see e.g. https://en.cppreference.com/w/c/language/conversion#Default_argument_promotions). This patch restricts the layouts that can be used as variadic layouts to what is allowed by the C specification.
>> 
>> The fallback linker is also updated to use to correct function to link variadic calls (not doing this turned out not to be a problem so far, but it is problematic for instance on Mac/AArch64 when using the fallback linker). Adding the restriction on layouts for all linkers is also partly motivated by the fallback linker rejecting such unsupported variadic layouts already.
>> 
>> I've added a small paragraph to the Linker javadoc as well that explains the restriction. Comments on that are welcome, but please explain.
>> 
>> The tests are updated to no longer try to link variadic functions with the illegal layouts, and I've added some more negative tests to TestIllegalLink.
>> 
>> Testing:
>> - local testing on Windows/x64
>> - tier1-3 + jdk-tier5 (ongoing)
>> - manual test run on mac/aarch64 with the fallback linker to verify the correctness of the fallback linker changes.
>
> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rework javadoc

Looks good - I left an optional comment. feel free to ignore (or to deal with that as part of some other PR).

src/java.base/share/classes/java/lang/foreign/Linker.java line 373:

> 371:  * <li>With an empty formal parameter list, such as: {@code void foo();}</li>
> 372:  * </ol>
> 373:  * The latter is often called a <em>prototype-less</em> function as well. The arguments passed in place of the ellipsis,

Would it make sense to move the prototype-less name in the second bullet above?

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PR Comment: https://git.openjdk.org/jdk/pull/14225#issuecomment-1572258397
PR Review Comment: https://git.openjdk.org/jdk/pull/14225#discussion_r1213320545