ghc @8.6.5_1: Built ghc not working on Catalina

[abusse (Anselm Busse)]

Compiled on macOS 10.15 with system compiler (Xcode 11.1) completes bootstrap, but the compiler later fails to run simple programs with a memory-related error:

ghc: mmap 131072 bytes at 0x0: Operation not permitted
ghc: Try specifying an address with +RTS -xm<addr> -RTS
ghc: internal error: m32_allocator_init: Failed to map
   (GHC version 8.6.5 for x86_64_apple_darwin)

Homebrew seems to have the same issue: ​https://github.com/Homebrew/homebrew-core/pull/44802

The issue is discussed upstream: ​https://gitlab.haskell.org/ghc/ghc/issues/17353 However, it seems to be an issue during building and not in the ghc code.

[cjones051073 (Chris Jones)]

Looks like just another instance of the Xcode 11 bug related to stack-check.

Simple solution, until either Apple fix it or upstream do something is blacklist Xcode 11 clang.

[essandess (Steve Smith)]

Another workaround: just install with the +prebuilt variant and hope that it runs.

[cjones051073 (Chris Jones)]

Replying to essandess:

Another workaround: just install with the +prebuilt variant and hope that it runs.

Last resort. Please try and fix the build itself. If it is just the Xcode 11 issue again, based on experience with other ports either just blacklisting Xcode 11 clang, so macports clang 9.0 is used, or appending the compiler option -fno-stack-check will do the job.

[mouse07410 (Mouse)]

IMHO, blacklisting Xcode-11 would be a very bad idea. That's the way Apple chose to proceed. I don't even know if XCode-10 would work on Catalina. We got to deal with it.

Adding -fstack-no-check appears the best solution/workaround, at least for now.

[cjones051073 (Chris Jones)]

An Apple insider as confirmed its a bug in Xcode 11. So blacklisting it is perfectly reasonable.

[cjones051073 (Chris Jones)]

Also note, just to be clear, the information we have is it should be fixed in Xcode 11.2 (time will tell on this). At this point the blacklist can be made specific to the clang version range affected.

Also, blacklisting Xcode 11 does not mean you have to install Xcode 10 !! It just means, for the port that does it, port will not use the Xcode clang versions blacklisted, and fallback to another compiler selection, which in this case will be MacPorts own build of clang 9.0. This works fine, we use it now in a number of places for exactly this issue.

[mouse07410 (Mouse)]

Chris, ok thanks, that makes sense. If Xcode-11.2 fixed the problem, it's fine to blacklist Xcode-11.{0,1}. Residually if having Macports clang-9 resolves the issue anyway

[ryandesign (Ryan Schmidt)]

Xcode 11.2.1 is out and is installed on our Catalina buildbot worker. But unfortunately ​ghc just got built with it and ​still has this problem.