Clang build of arm64 kernel fails

[Andrey Konovalov]

Hi Marc!

I've tried to pull in new upstream commits and the kernel build
started failing for me with the following errors (see below).

It seems that the reason is your commit "arm64: Add
ARM_SMCCC_ARCH_WORKAROUND_1 BP hardening support". It seems that Clang
doesn't like 32 bits registers being used in 64 bits build.

Would you mind sending a fix?

Thanks!

arch/arm64/kernel/cpu_errata.c:156:2: error: unknown register name 'r0' in asm
        arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
        ^
./include/linux/arm-smccc.h:276:32: note: expanded from macro
'arm_smccc_1_1_smc'
#define arm_smccc_1_1_smc(...)  __arm_smccc_1_1(SMCCC_SMC_INST, __VA_ARGS__)
                                ^
./include/linux/arm-smccc.h:255:3: note: expanded from macro '__arm_smccc_1_1'
                __declare_args(__count_args(__VA_ARGS__), __VA_ARGS__); \
                ^
./include/linux/arm-smccc.h:240:37: note: expanded from macro '__declare_args'
#define __declare_args(count, ...)  ___declare_args(count, __VA_ARGS__)
                                    ^
./include/linux/arm-smccc.h:239:37: note: expanded from macro '___declare_args'
#define ___declare_args(count, ...) __declare_arg_ ## count(__VA_ARGS__)
                                    ^
<scratch space>:136:1: note: expanded from here
__declare_arg_0
^
./include/linux/arm-smccc.h:197:32: note: expanded from macro '__declare_arg_0'
        register u32           r0 asm("r0") = a0;