rust: Add PowerPC support

For now only Big Endian 32-bit PowerPC is supported, as that is the only
hardware I have.  This has been tested on the Nintendo Wii so far, but I
plan on also using it on the GameCube, Wii U and Apple G4.

These changes aren’t the only ones required to get the kernel to compile
and link on PowerPC, libcore will also have to be changed to not use
integer division to format u64, u128 and core::time::Duration, otherwise
__udivdi3() and __umoddi3() will have to be added.  I have tested this
change by replacing the three implementations with unimplemented!() and
it linked just fine.

Signed-off-by: Link Mauve <linkmauve@linkmauve.fr>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260210090023.2587534-3-mkchauras@gmail.com

Author: linkmauve

Documentation/rust/arch-support.rst

@@ -18,6 +18,7 @@ Architecture   Level of support  Constraints
 ``arm``        Maintained        ARMv7 Little Endian only.
 ``arm64``      Maintained        Little Endian only.
 ``loongarch``  Maintained        \-
+``powerpc``    Maintained        32-bit Big Endian only.
 ``riscv``      Maintained        ``riscv64`` and LLVM/Clang only.
 ``um``         Maintained        \-
 ``x86``        Maintained        ``x86_64`` only.

arch/powerpc/Kconfig

@@ -284,6 +284,7 @@ config PPC
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE
 	select HAVE_RSEQ
+	select HAVE_RUST			if PPC32
 	select HAVE_SAMPLE_FTRACE_DIRECT	if HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_SAMPLE_FTRACE_DIRECT_MULTI	if HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_SETUP_PER_CPU_AREA		if PPC64

arch/powerpc/Makefile

@@ -61,6 +61,8 @@ else
 KBUILD_LDFLAGS_MODULE += $(objtree)/arch/powerpc/lib/crtsavres.o
 endif
 
+KBUILD_RUSTFLAGS += --target=powerpc-unknown-linux-gnu
+
 ifdef CONFIG_CPU_LITTLE_ENDIAN
 KBUILD_CPPFLAGS	+= -mlittle-endian
 KBUILD_LDFLAGS	+= -EL

rust/Makefile

@@ -402,13 +402,15 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 	-fstrict-flex-arrays=% -fmin-function-alignment=% \
 	-fzero-init-padding-bits=% -mno-fdpic \
 	-fdiagnostics-show-context -fdiagnostics-show-context=% \
-	--param=% --param asan-% -fno-isolate-erroneous-paths-dereference
+	--param=% --param asan-% -fno-isolate-erroneous-paths-dereference \
+	-ffixed-r2 -mmultiple -mno-readonly-in-sdata
 
 # Derived from `scripts/Makefile.clang`.
 BINDGEN_TARGET_x86	:= x86_64-linux-gnu
 BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
 BINDGEN_TARGET_arm	:= arm-linux-gnueabi
 BINDGEN_TARGET_loongarch	:= loongarch64-linux-gnusf
+BINDGEN_TARGET_powerpc	:= powerpc-linux-gnu
 BINDGEN_TARGET_um	:= $(BINDGEN_TARGET_$(SUBARCH))
 BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))