How to use clang 8?

Environments Linux
1

I’m trying to use clang 8 in my linux build (leaving out unrelated stuff):

matrix:
include:
- os: linux
dist: xenial
addons:
apt:
sources:
- ubuntu-toolchain-r-test
- llvm-toolchain-xenial-8
packages:
- clang-8
env:
- MATRIX_EVAL=“CC=clang-8 && CXX=clang+±8”

before_install:

  • eval “${MATRIX_EVAL}”

script:

  • make archive DEBUG=0 OS=LINUX CC=clang-8 && CXX=clang+±8

According to the log, this actually uses clang-8, but compilation fails with

fatal error: ‘cstddef’ file not found

I have no idea how to proceed on that. Using the default installed clang 7 works without any problems…

2

There is a problem with the include path provided to the compiler.

I’ll have to remark I’ve not run into this.

Possibilities:

  • I’m using CMake it might add the required paths.
  • You or a dependency could be trying to use libc++ when clang 8 is detected.
3

Yes, I am using libc++; isn’t that part of the llvm toolchain? How would I install that, I don’t see anything promising in the source safelist? I’m sorry for sounding dense, I do all my development work on macOS and just wait for the next Xcode; never had to worry about manually installing a new compiler and everything it needs, never used apt etc…

4

Please link to the build, copypasting things here gives incomplete information.

This line looks suspicious, probably should have been DEBUG=0 OS=LINUX CC=clang-8 CXX=clang++8 make archive or make archive DEBUG=0 OS=LINUX CC=clang-8 CXX=clang++8.

Also eval “${MATRIX_EVAL}” has no effect. A var assignment should use export to have an effect on a child process like make.

(Btw these both are the same for MacOS so you can’t plead ignorance here :wink: )

5

It’s a private project, unfortunately I cannot link to it…

make archive DEBUG=0 OS=LINUX CC=clang-8 && CXX=clang+±8

This line looks suspicious

Oh ffs… yeah, I just copy/pasted from the matrix line, ofc the “&&” is wrong here…

(Btw these both are the same for MacOS so you can’t plead ignorance here :wink: )

I plead half ignorance, I said “Xcode” :wink:
The “&&” was stupid and indeed I should have seen that. That weird “plus-minus” sign is a function of this board, it was “++ -” (without the space) and that’s where I still plead ignorance, I have no idea how those versions are really named.

Using just “++” results in

clang++8: Command not found

so it seems “clang+±8” was correct, that at least starts compiling. Leaving out the “&&” changes nothing, I still get

fatal error: ‘cstddef’ file not found

I am almost sure I also have to install an updated version of libc++ at a place where “llvm-toolchain-xenial-8” expects it; I have no idea how, though…

6

Thinking the toolchain should include libcc+, maybe it needs to be explicitly “activated” I tried:

      packages:
        - clang-8
        - libc++1

…still cannot find cstddef :frowning:

7

Your thought is right, all parts of the toolchain are installed separately.
See the documentation on https://apt.llvm.org for the naming:

packages:
  - clang-8
  - libc++-8-dev
  - libc++abi-8-dev
1 Like
8

This is strange, this was’t the case in LLVM 7: How can I setup LLVM 7 as default C / C++ compiler in Bionic - #2 by native-api

And checking http://apt.llvm.org/buster/dists/llvm-toolchain-buster-8/main/binary-amd64/Packages shows that clang-8 does depend on libstdc++-8-dev (but not libc++-8-dev).

Without seeing the build and the codebase, I cannot say more.

Actually, you still can link to the build, but only Travis support staff will be able to open the link.

9

Ah, that’s it! Now it compiles; throws some errors, but those seem to be in my code, not a problem of the toolchain…

Thanks for the help

10

Actually, you still can link to the build, but only Travis support staff will be able to open the link.

Fair enough :slight_smile: