instruction requires a CPU feature not currently enabled in arch/mips/kernel/cpu-probe.c

[tpimh]

Build of mipsel kernel with integrated-as enabled failing:

arch/mips/kernel/cpu-probe.c:1059:2: error: instruction requires a CPU feature not currently enabled
        probe_gc0_config(config, config0, MIPS_CONF_M);
        ^
arch/mips/kernel/cpu-probe.c:1034:8: note: expanded from macro 'probe_gc0_config'
        tmp = read_gc0_##name();                                        \
              ^
<scratch space>:283:1: note: expanded from here
read_gc0_config
^
./arch/mips/include/asm/mipsregs.h:2160:28: note: expanded from macro 'read_gc0_config'
#define read_gc0_config()               __read_32bit_gc0_register($16, 0)
                                        ^
./arch/mips/include/asm/mipsregs.h:2011:3: note: expanded from macro '__read_32bit_gc0_register'
                _ASM_SET_VIRT                                           \
                ^
./arch/mips/include/asm/mipsregs.h:2003:36: note: expanded from macro '_ASM_SET_VIRT'
#define _ASM_SET_VIRT ".set\tvirt\n\t"
                                   ^
<inline asm>:4:2: note: instantiated into assembly here
        mfgc0   $2, $16, 0
        ^

[nickdesaulniers]

I suspect that a .arch directive is required in the asm string. It may be set at the top of the file, and Clang doesn't support that as it treats each inline asm block as its own TU. We seen this kind of bug before for other arch's.

Though it also looks like something else more complicated is going on:

linux/arch/mips/include/asm/mipsregs.h

Line 1978 in a99d808

#ifndef TOOLCHAIN_SUPPORTS_VIRT

[nickdesaulniers]

Reproducible still with:

$ ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- make CC=clang LLVM_IAS=1 -j72 defconfig all

[nickdesaulniers]

-DTOOLCHAIN_SUPPORTS_VIRT is getting set for arch/mips/kernel/cpu-probe.o.

It seems perhaps that LLVM accepts these instructions for mips32r5.

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index 9c8099a6ffed..acdf8c69220b 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -2077,7 +2077,7 @@ _ASM_MACRO_0(tlbginvf, _ASM_INSN_IF_MIPS(0x4200000c)
 ({ int __res;                                                          \
        __asm__ __volatile__(                                           \
                ".set\tpush\n\t"                                        \
-               ".set\tmips32r2\n\t"                                    \
+               ".set\tmips32r5\n\t"                                    \
                _ASM_SET_VIRT                                           \
                "mfgc0\t%0, " #source ", %1\n\t"                        \
                ".set\tpop"                                             \
@@ -2090,7 +2090,7 @@ _ASM_MACRO_0(tlbginvf, _ASM_INSN_IF_MIPS(0x4200000c)
 ({ unsigned long long __res;                                           \
        __asm__ __volatile__(                                           \
                ".set\tpush\n\t"                                        \
-               ".set\tmips64r2\n\t"                                    \
+               ".set\tmips64r5\n\t"                                    \
                _ASM_SET_VIRT                                           \
                "dmfgc0\t%0, " #source ", %1\n\t"                       \
                ".set\tpop"                                             \
@@ -2103,7 +2103,7 @@ _ASM_MACRO_0(tlbginvf, _ASM_INSN_IF_MIPS(0x4200000c)
 do {                                                                   \
        __asm__ __volatile__(                                           \
                ".set\tpush\n\t"                                        \
-               ".set\tmips32r2\n\t"                                    \
+               ".set\tmips32r5\n\t"                                    \
                _ASM_SET_VIRT                                           \
                "mtgc0\t%z0, " #register ", %1\n\t"                     \
                ".set\tpop"                                             \
@@ -2115,7 +2115,7 @@ do {                                                                      \
 do {                                                                   \
        __asm__ __volatile__(                                           \
                ".set\tpush\n\t"                                        \
-               ".set\tmips64r2\n\t"                                    \
+               ".set\tmips64r5\n\t"                                    \
                _ASM_SET_VIRT                                           \
                "dmtgc0\t%z0, " #register ", %1\n\t"                    \
                ".set\tpop"                                             \

With that, I see warnings from #1414 and #1415 but the kernel builds and boots.

[nickdesaulniers]

submitted: https://lore.kernel.org/lkml/20210628215029.2722537-1-ndesaulniers@google.com/T/#u

[nickdesaulniers]

accepted: https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=c994a3ec7ecc8bd2a837b2061e8a76eb8efc082b

[nickdesaulniers]

c994a3e