On Wed, 28 Oct 2026 18:08:39 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: > > Rename withSign in the tests as well javadoc for JAVA_XYZ constants should perhaps be enhanced to say what the sign is src/java.base/share/classes/java/lang/foreign/ValueLayout.java line 131: > 129: * can be either signed or unsigned. The signedness of an integral > 130: * value layout has no effect on the memory access operations > 131: * provided by this package. However, signedness is relevant when `provided by this package` sounds odd. Maybe just "on memory access operation involving that integral layout" (maybe add a link on accessing memory segment javadoc section?). src/java.base/share/classes/java/lang/foreign/ValueLayout.java line 132: > 130: * value layout has no effect on the memory access operations > 131: * provided by this package. However, signedness is relevant when > 132: * values represented by integral layouts are widened. For example, instead of "represented" I think "associated with" works better src/java.base/share/classes/java/lang/foreign/ValueLayout.java line 136: > 134: * determines whether the value should be sign extended as specified > 135: * by {@jls 5.1.2}, or zero extended as specified by the > 136: * {@link Integer#toUnsignedLong(int)} method. A user who is > interested Suggestion: * {@link Integer#toUnsignedLong(int)} method. Users interested src/java.base/share/classes/java/lang/foreign/ValueLayout.java line 137: > 135: * by {@jls 5.1.2}, or zero extended as specified by the > 136: * {@link Integer#toUnsignedLong(int)} method. A user who is > interested > 137: * in widening values represented by integral value layouts may wish Again -- "represented" ------------- PR Review: https://git.openjdk.org/jdk/pull/33417#pullrequestreview-5688121977 PR Review Comment: https://git.openjdk.org/jdk/pull/33417#discussion_r4404798059 PR Review Comment: https://git.openjdk.org/jdk/pull/33417#discussion_r4404801988 PR Review Comment: https://git.openjdk.org/jdk/pull/33417#discussion_r4404811444 PR Review Comment: https://git.openjdk.org/jdk/pull/33417#discussion_r4404816466
