Support GCC for PowerPC

`LLVM=1` is not supported by the kernel for PPC, so we disable it
(at the moment, it builds, but does not boot).

Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

.github/workflows/ci.yaml

@@ -10,14 +10,19 @@ jobs:
 
     strategy:
       matrix:
-        arch: [x86_64, arm64]
+        arch: [x86_64, arm64, ppc64le]
         toolchain: [gcc, clang, llvm]
         config: [debug, release]
         rustc: [2021-02-20]
         output: [src] # [src, build]
         install: [rustup] # [rustup, standalone]
         sysroot: [common] # [common, custom]
 
+        # Exclude `LLVM=1` where not supported.
+        exclude:
+          - arch: ppc64le
+            toolchain: llvm
+
         # A few independent combinations to avoid exploding the matrix:
         #   - The other option for `output`.
         #   - Different nightlies for `rustc`.
@@ -48,14 +53,6 @@ jobs:
             install: standalone
             sysroot: custom
 
-          - arch: ppc64le
-            toolchain: clang
-            config: debug
-            rustc: 2021-02-20
-            output: src
-            install: rustup
-            sysroot: common
-
     steps:
       # Setup: checkout
       - uses: actions/checkout@v2

Documentation/rust/arch-support.rst

@@ -23,7 +23,7 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
      - None
    * - ``powerpc``
      - Maintained
-     - ``ppc64le`` only, ``RUST_OPT_LEVEL >= 2``, Clang only
+     - ``ppc64le`` only, ``RUST_OPT_LEVEL >= 2``
    * - ``x86``
      - Maintained
      - ``x86_64`` only

init/Kconfig

@@ -58,7 +58,7 @@ config LLD_VERSION
 	default 0
 
 config HAS_RUST
-	depends on ARM64 || X86_64 || (PPC64 && CPU_LITTLE_ENDIAN && CC_IS_CLANG)
+	depends on ARM64 || X86_64 || (PPC64 && CPU_LITTLE_ENDIAN)
 	def_bool $(success,$(RUSTC) --version)
 
 config RUSTC_VERSION

rust/Makefile

@@ -54,6 +54,11 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 	-Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized \
 	-Werror=designated-init -Wno-zero-length-bounds \
 	--param=% --param asan-%
+
+# PowerPC
+bindgen_skip_c_flags += -mtraceback=no -mno-pointers-to-nested-functions \
+	-mno-string -mno-strict-align
+
 bindgen_extra_c_flags = $(TENTATIVE_CLANG_FLAGS) -Wno-address-of-packed-member
 bindgen_c_flags = $(filter-out $(bindgen_skip_c_flags), $(c_flags)) \
 	$(bindgen_extra_c_flags)