RFR: 8308031: Linkers should reject unpromoted variadic parameters [v5]

[Jorn Vernee]

> 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:

  automatically apply variadic promotions

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14225/files
  - new: https://git.openjdk.org/jdk/pull/14225/files/1f1e22eb..38d759d6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14225&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14225&range=03-04

  Stats: 177 lines in 8 files changed: 110 ins; 51 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/14225.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14225/head:pull/14225

PR: https://git.openjdk.org/jdk/pull/14225