From: Joel Stanley joel@jms.id.au
[ Upstream commit 960e30029863db95ec79a71009272d4661db5991 ]
Ever since commit 15a3204d24a3 ("powerpc/64s: Set assembler machine type to POWER4") we force -mpower4 to be passed to the assembler irrespective of the CFLAGS used (for Book3s 64).
When building a powerpc64 kernel with clang, clang will not add -many to the assembler flags, so any instructions that the compiler has generated that are not available on power4 will cause an error:
/usr/bin/as -a64 -mppc64 -mlittle-endian -mpower8 \ -I ./arch/powerpc/include -I ./arch/powerpc/include/generated \ -I ./include -I ./arch/powerpc/include/uapi \ -I ./arch/powerpc/include/generated/uapi -I ./include/uapi \ -I ./include/generated/uapi -I arch/powerpc -I arch/powerpc \ -maltivec -mpower4 -o init/do_mounts.o /tmp/do_mounts-3b0a3d.s /tmp/do_mounts-51ce54.s:748: Error: unrecognized opcode: `isel'
GCC does include -many, so the GCC driven gas call will succeed:
as -v -I ./arch/powerpc/include -I ./arch/powerpc/include/generated -I ./include -I ./arch/powerpc/include/uapi -I ./arch/powerpc/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -I arch/powerpc -I arch/powerpc -a64 -mpower8 -many -mlittle -maltivec -mpower4 -o init/do_mounts.o
Note that isel is power7 and above for IBM CPUs. GCC only generates it for Power9 and above, but the above test was run against the clang generated assembly.
Peter Bergner explains:
When using -many -mpower4, gas will first try and find a matching power4 mnemonic and failing that, it will then allow any valid mnemonic that gas knows about. GCC's use of -many predates me though.
IIRC, Alan looked at trying to remove it, but I forget why he didn't. Could be either a gcc or gas issue at the time. I'm not sure whether issue still exists or not. He and I have modified how gas works internally a fair amount since he tried removing gcc use of -many.
I will also note that when using -many, gas will choose the first mnemonic that matches in the mnemonic table and we have (mostly) sorted the table so that server mnemonics show up earlier in the table than other mnemonics, so they'll be seen/chosen first.
By explicitly setting -many we can build with Clang and GCC while retaining the -mpower4 option.
Signed-off-by: Joel Stanley joel@jms.id.au Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/Makefile | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index 11a1acba164a..d2824b0cc142 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -238,7 +238,11 @@ cpu-as-$(CONFIG_4xx) += -Wa,-m405 cpu-as-$(CONFIG_ALTIVEC) += $(call as-option,-Wa$(comma)-maltivec) cpu-as-$(CONFIG_E200) += -Wa,-me200 cpu-as-$(CONFIG_E500) += -Wa,-me500 -cpu-as-$(CONFIG_PPC_BOOK3S_64) += -Wa,-mpower4 + +# When using '-many -mpower4' gas will first try and find a matching power4 +# mnemonic and failing that it will allow any valid mnemonic that GAS knows +# about. GCC will pass -many to GAS when assembling, clang does not. +cpu-as-$(CONFIG_PPC_BOOK3S_64) += -Wa,-mpower4 -Wa,-many cpu-as-$(CONFIG_PPC_E500MC) += $(call as-option,-Wa$(comma)-me500mc)
KBUILD_AFLAGS += $(cpu-as-y)