All of the targets in the Foundation project (both those here as well as those in swift-foundation) use ORIGIN-based rpath values. Is there something special about the Foundation library, or should this be provided for all of these targets?

-z origin is a flag that is useful in the odd case that the reference to $ORIGIN does not occur in DT_NEEDED or DT_RUNPATH (DT_RPATH also applies, but that is considered deprecated) and is expected to possibly occur at runtime through libdl (i.e. dlopen). In such cases the computation may be elided as the value is unneeded and could cause a failure otherwise due to the missing value.

On OpenBSD, -z origin is also required to properly resolve $ORIGIN.

I'm fairly sure this will be required for the other targets, and only the main Foundation library has posed a problem while trying to get the toolchain stood up end to end, so I've only added it for Foundation so far.

It probably is the case I should add them for the other targets, but I need to double-check.

Ah, right, this is Open, not Free. Open and DragonFly both need -z origin.

I think I forgot to close the loop here and mention that I added the flag for the other targets.

Actually, I'm not sure this is working as intended. This is only evaluated once before any targets are defined, right?

For now, I've just made it unconditional.

Yes, it would be evaluated once. It could be that my regex is incorrect. But, CMAKE_INSTALL_RPATH is user supplied.

My point is that I am guessing that cmake is evaluating CMAKE_INSTALL_RPATH at the time this expression is evaluated -- before the INSTALL_RPATH target property is evaluated on the Foundation target. If CMAKE_INSTALL_RPATH doesn't already mention $ORIGIN, this won't add the linker flag globally.

If we were going to apply the linker flag to all targets and only all targets at the top level, we'd need to iterate all targets and get the INSTALL_RPATH target property and add the linker flag for only those targets whose INSTALL_RPATH property mentions $ORIGIN -- but that's a whole lot of messing around.

Hence, it might just be simpler to just add the flag unconditionally for now and be done with it. It's not ideal but it'll work, and the scope of the diff will be smaller.

Ah, I see your confusion now. CMAKE_INSTALL_RPATH is not a target specific property. It is a default value property. The user specifies that and the value is used to initialise the property on all targets. That is:

cmake -B out -G Ninja -S . -D CMAKE_INSTALL_RPATH="$ORIGIN" -D CMAKE_SYSTEM_NAME=OpenBSD -D CMAKE_SYSTEM_PROCESSOR=AMD64

The point I was missing was forgetting to bring the INSTALL_RPATH property on each target up to the top level and actually set that default. D'oh! I've done that now. plutil still needs a target-specific INSTALL_RPATH, but it doesn't hurt to just override the default for that specific target.

I think this should all make sense now.