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Pass unions by value with the C ABI's register classes #9702

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Merged
headius merged 10 commits into from
Oct 2, 2026
Merged

Pass unions by value with the C ABI's register classes #9702

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45eab4b
Add union-by-value specs and fixtures
aminmansuri Sep 14, 2026
1494429
Pass unions by value with the C ABI's register classes
aminmansuri Sep 14, 2026
90d4960
Add specs for a mixed union at offset four in a by-value struct
aminmansuri Sep 16, 2026
1ff5b7f
Classify SysV x86_64 union cells by cell, not by eightbyte
aminmansuri Sep 16, 2026
b900cb0
Pass the CPU and OS into the union filler choice
aminmansuri Sep 16, 2026
835b02e
Test the union filler per CPU against the C ABIs
aminmansuri Sep 16, 2026
388c957
Use the float filler only where a union can be a floating aggregate
aminmansuri Sep 16, 2026
c4c4e4b
Drop the unreachable long double handling from newUnion
aminmansuri Sep 16, 2026
46a9ec4
Cover riscv64 in the union filler test
aminmansuri Sep 16, 2026
134c2f2
Name the filler cells in UnionFillerTest failure messages
aminmansuri Sep 16, 2026
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Pass the CPU and OS into the union filler choice 
No behaviour change: the one-argument newUnion hands the host platform
to the overload, which tests can call with any CPU and OS.
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@aminmansuri
aminmansuri committed Sep 16, 2026
commit b900cb0f751b9455417b32f0451a53f366b2125b
12 changes: 8 additions & 4 deletions core/src/main/java/org/jruby/ext/ffi/jffi/FFIUtil.java
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Original file line number Diff line number Diff line change
Expand Up @@ -139,9 +139,6 @@ static final com.kenai.jffi.Aggregate newStruct(org.jruby.ext.ffi.StructLayout l
}
}

private static final boolean SYSV_X86_64 = Platform.getPlatform().getCPU() == Platform.CPU_TYPE.X86_64
&& Platform.getPlatform().getOS() != Platform.OS_TYPE.WINDOWS;

private static final com.kenai.jffi.Type[] INTEGER_FILLERS = {
com.kenai.jffi.Type.SINT8, com.kenai.jffi.Type.SINT16, com.kenai.jffi.Type.SINT32,
com.kenai.jffi.Type.SINT64, com.kenai.jffi.Type.LONGDOUBLE,
Expand All @@ -157,7 +154,14 @@ private record Leaf(NativeType type, int offset, int size) {}
* @return A new Struct descriptor.
*/
static final com.kenai.jffi.Aggregate newUnion(org.jruby.ext.ffi.StructLayout layout) {
return newUnion(layout, Platform.getPlatform().getCPU(), Platform.getPlatform().getOS());
}

/** The same choice for a given CPU and OS, so the ABI rules can be checked off the host. */
static final com.kenai.jffi.Aggregate newUnion(org.jruby.ext.ffi.StructLayout layout,
Platform.CPU_TYPE cpu, Platform.OS_TYPE os) {
final int size = layout.getNativeSize(), alignment = layout.getNativeAlignment();
final boolean sysvX86_64 = cpu == Platform.CPU_TYPE.X86_64 && os != Platform.OS_TYPE.WINDOWS;

java.util.List<Leaf> leaves = new java.util.ArrayList<>();
for (StructLayout.Member m : layout.getMembers()) {
Expand All @@ -175,7 +179,7 @@ static final com.kenai.jffi.Aggregate newUnion(org.jruby.ext.ffi.StructLayout la
// on AArch64 (and PPC64 ELFv2), SSE class on SysV x86_64. Keep the real type.
filler = getFFIType(homogeneous);

} else if (SYSV_X86_64 && alignment >= 4 && alignment <= 8 && size <= 16) {
} else if (sysvX86_64 && alignment >= 4 && alignment <= 8 && size <= 16) {
// SysV x86_64 classifies each eightbyte separately: SSE only if every field overlapping it
// is float or double, INTEGER otherwise. Decide per cell: libffi merges the cells into
// eightbytes at the union's offset inside an enclosing struct, so the result holds there too.
Expand Down