cmd/compile: support -buildmode=pie on OpenBSD

[catinello]

What version of Go are you using (go version)?

$ go version go1.20.1 openbsd/amd64

Does this issue reproduce with the latest release?

Yes, I think so.

What operating system and processor architecture are you using (go env)?

OpenBSD 7.3 on amd64

What did you do?

I tried to build a PIE binary with -buildmode=pie

What did you expect to see?

I was expecting to build a binary with PIE enabled.

What did you see instead?

-buildmode=pie not supported on openbsd/amd64

Is there any particular reason that buildmode=pie is not supported on openbsd? Building with that buildmode returns that the buildmode=pie is not supported.

clang on OpenBSD/amd64 defaults and produces PIE static/dynamic binaries without issue. But even external linking in Go suppresses PIE with LDFlags -Wl,-nopie. You can append -Wl,-pie through -extldflags option, the result will be expectedly an invalid function entry symbol table or a segmentation fault.

I could not find an open issue that works on this or explains the situation for the missing support. There are some that are years old and closed or some old mailing list entries. I get that openbsd is a secondary port, but why is there not even an issue that addresses the state/progress and situation?

I'm just genuinely interested to see progress at this.

Thank you.

[bcmills]

(attn @golang/openbsd)

[qbit]

Around 2020-02-01 I started working on PIE mode for Go amd64. Here is the diff.

I got everything working:

• It is able to produce binaries.
• Tests pass.

However, about 50% of the time binaries produced with it die with a SIGSEGV. Interestingly it works fine on single CPU machines.

[catinello]

Awesome! Your patch allows/fixes the necessary flags as it seems. Does the patch work against 1.20.1 that is currently in ports? Did you try with 7.3 yet? mmap/mprotect was SMP unlocked.

[qbit]

I haven't updated the patch to work with newer Go versions.

[catinello]

Is there more information somewhere? Why was PIE disabled in the first place? There must be a reason?

The patch definitely needs some work and I doubt that enabling the flags will just make everything work.

[catinello]

I think I found the origin in #17847

But could DT_TEXTREL really be the issue here? OpenBSD builds PIE by default and Go does call the external linker on OpenBSD.

Maybe this was just collateral damage?

[qbit]

The patch definitely needs some work and I doubt that enabling the flags will just make everything work.

Indeed it did with with enabling the flags .. just inconsistently on MP machines. The bins were PIE and ran as expected on single proc machines.

I can't speak to why it was disabled in the first place.

[ikmckenz]

Also running into this issue