[PATCH] D41623: [cmake] [libcxxabi] Fix path problems when cross compiling.

[Don Hinton via Phabricator via cfe-commits]

hintonda added a comment.

In https://reviews.llvm.org/D41623#982189, @phosek wrote:

> Isn't `NO_DEFAULT_PATH` more appropriate here? That's what libc++ uses as well.


Unfortunately no.

When cross compiling, it's important to look for headers in CMAKE_SYSROOT and/or CMAKE_FIND_ROOT_PATH, or you'll end up finding for headers on the host, not the target.  To make sure this works as expected, cmake recommends using `set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)` -- see https://cmake.org/Wiki/CMake_Cross_Compiling for details.

With `CMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY` and `CMAKE_SYSROOT` set, all `find_XXX()` commands will add the `CMAKE_SYSROOT` prefix to all the paths used in the search.  So, if you are trying to look in a local source directory, you'll never find it, because `find_XXX()` will actually use `${CMAKE_SYSROOT}/<my local path>`, which is always the wrong place.

These `find_path()` invocations are looking in specific places which exist on the host system, not the target system.


Repository:
  rCXXA libc++abi

https://reviews.llvm.org/D41623