[PATCH v4 12/12] selftests/nolibc: customize CROSS_COMPILE for 32/64-bit powerpc

[Zhangjin Wu <falcon@xxxxxxxxxxx>]

The little-endian powerpc64le compilers provided by Ubuntu and Fedora
are able to compile big endian kernel and big endian nolibc-test [1].

These default CROSS_COMPILE settings allow to test target architectures
with:

    $ cd /path/to/tools/testing/selftests/nolibc/

    $ for arch in ppc ppc64 ppc64le; do \
        make run-user ARCH=$arch | grep "status: "; \
      done

If want to use another cross compiler, please simply pass CROSS_COMPILE
or CC as before.

For example, it is able to build 64-bit nolibc-test with the big endian
powerpc64-linux-gcc crosstool from [2]:

    $ wget -c https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/13.1.0/x86_64-gcc-13.1.0-nolibc-powerpc64-linux.tar.xz
    $ tar xvf x86_64-gcc-13.1.0-nolibc-powerpc64-linux.tar.xz
    $ export PATH=$PWD/gcc-13.1.0-nolibc/powerpc64-linux/bin/:$PATH

    $ export CROSS_COMPILE_ppc64=powerpc64-linux-
    $ export CROSS_COMPILE_ppc64le=powerpc64-linux-
    $ for arch in ppc64 ppc64le; do \
        make run-user ARCH=$arch | grep "status: "; \
      done

Or specify CC directly with full path:

    $ export CC=$PWD/gcc-13.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc
    $ for arch in ppc64 ppc64le; do \
        make run-user ARCH=$arch | grep "status: "; \
      done

[1]: https://github.com/open-power/skiboot
[2]: https://mirrors.edge.kernel.org/pub/tools/crosstool/

Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
---
 tools/testing/selftests/nolibc/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/nolibc/Makefile b/tools/testing/selftests/nolibc/Makefile
index 822cc4bae619..f44a09c39235 100644
--- a/tools/testing/selftests/nolibc/Makefile
+++ b/tools/testing/selftests/nolibc/Makefile
@@ -59,6 +59,9 @@ IMAGE            = $(IMAGE_$(XARCH))
 IMAGE_NAME       = $(notdir $(IMAGE))
 
 # CROSS_COMPILE: cross toolchain prefix by architecture
+CROSS_COMPILE_ppc       ?= powerpc-linux-gnu-
+CROSS_COMPILE_ppc64     ?= powerpc64le-linux-gnu-
+CROSS_COMPILE_ppc64le   ?= powerpc64le-linux-gnu-
 CROSS_COMPILE           ?= $(CROSS_COMPILE_$(XARCH))
 
 # make sure CC is prefixed with CROSS_COMPILE
-- 
2.25.1