[PATCH] D87164: Extending Baremetal toolchain's support for the rtlib option.

[Jon Roelofs via Phabricator via cfe-commits]

jroelofs added a comment.

In D87164#2268366 <https://reviews.llvm.org/D87164#2268366>, @mcarrasco wrote:

> @jroelofs no worries, thanks a lot for your time.
>
> Please tell me if I understood you correctly.
>
> It is acceptable just to append the -lgcc if -rtlib=libgcc is used, although the user is responsible to ensure that correct paths are provided so libgcc is found.

Kind of, yeah.

> I also agree with the above, although I just want to know if I got your words correctly. In addition, you suggest that the build system should invoke clang with a valid value in --resource-dir option in order find libgcc.

If you're putting together your own toolchain, then the right thing to do is to install libgcc into the folder where clang expects to find the compiler-rt builtins in the resource-dir. This is usually in a folder that's sibling to the compiler itself, something like lib/clang/$version/lib/baremetal, assuming clang lives at bin/clang.

> Could you point me where I can find more info regarding --resource-dir? So far I only found this:
>
>   clang --help-hidden | grep resource-dir
>     -print-resource-dir     Print the resource directory pathname
>     -resource-dir <value>   The directory which holds the compiler resource files
>
> Sincerly, I'm a little bit confused about: -sysroot, -gcc-toolchain and now -resource-dir

I don't know of any docs for it off the top of my head, but roughly speaking:

- resource-dir is where the compiler is instructed to find the compiler-support libraries (i.e. compiler-rt or libgcc)
- sysroot is where libc, the stl, unwinder, c++ abi support library etc should live. The folder that this points at should have the same layout as root would (i.e. with $sysroot/usr/lib, $sysroot/usr/include, etc), were you building for the target from the target (not that that makes much sense for baremetal, but you get the picture).
- -gcc-toolchain is where to look for a gcc toolchain for your target. This is mainly for linux targets that rely on an installed gcc toolchain, and isn't hooked up for the bare metal side of things. This isn't necessary if you have a self-contained clang toolchain built that doesn't rely on those bits of gcc.

> Thanks for your feedback!
> Manuel.




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