RFR: 8308031: Linkers should reject unpromoted variadic parameters

[Maurizio Cimadamore]

On Tue, 30 May 2023 17:25:35 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.

Looks good

src/java.base/share/classes/java/lang/foreign/Linker.java line 415:

> 413:  * It should be noted that values passed as variadic arguments undergo default argument promotion in C. Each value of
> 414:  * type {@code float} is converted to {@code double}, and each integral type smaller than {@code int} is converted to
> 415:  * {@code int}. As such, the native linker will reject attempts to link a function with variadic parameters which have

maybe "will reject attempts to link a variadic function if one or more parameter layouts in the provided function descriptor which correspond to a variadic argument is a value layout such that ..."

test/jdk/java/foreign/StdLibTest.java line 386:

> 384:             return arena.allocateUtf8String("str");
> 385:         }, "str"),
> 386:         CHAR(int.class, C_INT, "%c", arena -> (int) 'h', (int) 'h'), // promote to int, per C spec

is it important to retain this, given that there's already an INT case?

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Marked as reviewed by mcimadamore (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14225#pullrequestreview-1453564448
PR Review Comment: https://git.openjdk.org/jdk/pull/14225#discussion_r1211924259
PR Review Comment: https://git.openjdk.org/jdk/pull/14225#discussion_r1211927081