[libcxx-commits] [PATCH] D113253: [runtimes] Fix building initial libunwind+libcxxabi+libcxx with compiler implied -lunwind

[Louis Dionne via Phabricator via libcxx-commits]

ldionne added inline comments.


================
Comment at: runtimes/CMakeLists.txt:101-102
+
+check_c_compiler_flag("" LLVM_RUNTIMES_LINKING_WORKS)
+if (NOT LLVM_RUNTIMES_LINKING_WORKS)
+  # The compiler driver may be implicitly trying to link against libunwind, which
----------------
mstorsjo wrote:
> ldionne wrote:
> > I don't understand how this check works. Since you are disabling runtime linking, I would think that `check_c_compiler_flag` succeeding does NOT imply that runtime linking works?
> We don’t disable linking here - this is cmake’s standard compile+link test. We do one such test, adding no flags, to see if linking works out of the box.
> 
> If it succeeds, we have a complete toolchain and don’t need to do anything. If linking doesn’t seem to work, it could be an incomplete toolchain being built - in those cases, check if we could make it work by adding `--unwindlib=none`.
> 
> The reason for this indirection is that if we have a complete toolchain, adding that option can break things - if we’re setting up building with sanitizers (as in CI), adding that option breaks the sanitizers.
Don't you disable runtime linking in compiler checks on line 18 above?

```
include(EnableLanguageNolink)
project(Runtimes LANGUAGES NONE)
llvm_enable_language_nolink(C CXX ASM)
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D113253/new/

https://reviews.llvm.org/D113253