On Tue, 3 Nov 2026 14:00:55 GMT, Jorn Vernee <[email protected]> wrote:
>> Currently we do not directly support unsigned types in the Linker. The >> javadoc has this to say about it: >> >>> A native linker typically does not provide canonical layouts for C's >>> unsigned integral >> types. Instead, they are modeled using the canonical layouts associated >> with their >> corresponding signed integral types. For instance, the C type `unsigned >> long` >> maps to the canonical layout for `code long`. >> >> This was done under the earlier assumption that ABIs treat signed and >> unsigned types the same. However, it turns out that we missed certain cases >> where this does matter for some ABIs. More concretely: >> >> - Mac x64 and AArch64 ABIs require integral types smaller than `int` to be >> widened to `int` before being passed to a function >> [1](https://developer.apple.com/documentation/xcode/writing-64-bit-intel-code-for-apple-platforms), >> >> [2](https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms). >> Clang even extends this behavior to Linux x64 (although this appears to be >> a bug) >> [3](https://mail.openjdk.org/archives/list/[email protected]/message/RJNMKNUXN7R5PSJETZKX3PMBJ7P6GYJG/). >> - RISCV requires arguments smaller than XLEN to be extended to 32 bits >> according to their sign, and then sign extended to XLEN >> [4](https://docs.riscv.org/reference/abi/v1.0/riscv-cc-procedure-calling-convention.html). >> - PowerPC requires small integer types (char, short, int, long, enum) to be >> extended to long >> [5](https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#PARAM-PASS). >> >> In order to address these use cases we need to attach a bit of extra >> information to a linkage request that indicates the signedness of certain >> arguments. For this patch, we've chosen to attach that information directly >> to the argument layouts through a newly introduced `boolean isSigned()` >> method on a new `ValueLayout` subclass `OfIntegral` that is implemented by >> `OfByte`, `OfShort`, `OfInt`, and `OfLong`. >> >> This information is potentially used by the linker to implement the correct >> extension. In cases where it doesn't affect the way functions are linker the >> information is erased in order to provide more efficient caching, since >> signed and unsigned types can share the same downcall handle in that case. >> >> Testing: `jdk_foreign` test suite on Windows/Linux/Mac-x64, >> Mac/Linux-AArch64, Linux-x64 using the fallback linker. >> >> --------- >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](http... > > Jorn Vernee has updated the pull request incrementally with one additional > commit since the last revision: > > Fix canonical layouts + add test I've fixed a few more issues in the fallback linker identified by codex. There were also some canonical layouts that had the wrong sign. I've now added a comprehensive test that checks the canonical layouts against information extracted from the compiler on that platform (using a library). Finally, I fixed a copy-paste error in the new `TestZeroExtendLong` jtreg test definition, which was accidentally running the `TestZeroExtendInt` test. ------------- PR Comment: https://git.openjdk.org/jdk/pull/33417#issuecomment-6605807368
