LLVM compiler-rt#

The $pw_external_llvm_builtins/ directory provides the GN integration necessary to link against LLVM compiler-rt project. The intention here is to use the builtins provided by the LLVM compiler-rt project.

Using upstream LLVM compiler-rt#

If you want to use LLVM compiler-rt, you must do the following:

Submodule#

Add LLVM compiler-rt to your workspace with the following command.

$ git submodule add \
> https://llvm.googlesource.com/llvm-project/compiler-rt \
> third_party/llvm_builtins

Note

This git repository is maintained by Google and is a slice of upstream LLVM including only the compiler-rt subdirectory.

GN#

Set the GN var dir_pw_third_party_llvm_builtins to the location of the LLVM compiler-rt source. If you used the command above, this will be //third_party/llvm_builtins.

This can be set in your args.gn or .gn file:
```
dir_pw_third_party_llvm_builtins = "//third_party/llvm_builtins"
```
Set the pw_third_party_llvm_builtins_TARGET_BUILTINS to the pw_source_set that selectively adds the files required for the given architecture from the LLVM compiler-rt checkout directory.

For example, you can add the following in your args.gn or .gn file to use the builtins for ARMv7-M targets.
```
pw_third_party_llvm_builtins_TARGET_BUILTINS = "$pw_external_llvm_builtins:arm_builtins_armv7m"
```
Set the optional pw_third_party_llvm_builtins_ignore_list variable to the list of files included in pw_source_set in $pw_external_llvm_builtins/BUILD.gn.