invalid operand for slti in arch/mips/include/asm/mach-loongson64/kernel-entry-init.h

[emojifreak]

According to #1434, LLVM_IAS=1 seems supported on mips. CONFIG_MACH_LOONGSON64=y & CONFIG_CPU_LOONGSON64=y & CONFIG_LOONGSON3_ENHANCEMENT=y for mips64el-linux-gnuabi64 causes error in the integrated as such as

  AS      arch/mips/kernel/head.o
<instantiation>:16:12: error: invalid operand for instruction
 slti $12, (0x6300 | 0x0008)
           ^
arch/mips/kernel/head.S:86:2: note: while in macro instantiation
 kernel_entry_setup # cpu specific setup
 ^
<instantiation>:16:12: error: invalid operand for instruction
 slti $12, (0x6300 | 0x0008)
           ^
arch/mips/kernel/head.S:150:2: note: while in macro instantiation
 smp_slave_setup
 ^
make[2]: *** [scripts/Makefile.build:388: arch/mips/kernel/head.o] Error 1

  CC      arch/mips/kvm/tlb.o
In file included from arch/mips/kvm/tlb.c:13:
In file included from ./include/linux/sched.h:12:
In file included from ./arch/mips/include/generated/asm/current.h:1:
In file included from ./include/asm-generic/current.h:5:
In file included from ./include/linux/thread_info.h:27:
In file included from ./include/linux/bitops.h:33:
In file included from ./arch/mips/include/asm/bitops.h:19:
In file included from ./arch/mips/include/asm/barrier.h:11:
In file included from ./arch/mips/include/asm/addrspace.h:13:
In file included from ./arch/mips/include/asm/mach-loongson64/spaces.h:16:
In file included from ./arch/mips/include/asm/mach-generic/spaces.h:15:
./arch/mips/include/asm/mipsregs.h:2832:3: error: instruction requires a CPU feature not currently enabled
                __tlbgp()
                ^
./arch/mips/include/asm/mipsregs.h:2106:19: note: expanded from macro '__tlbgp'
#define __tlbgp()       _ASM_SET_VIRT "tlbgp\n\t"
                        ^
./arch/mips/include/asm/mipsregs.h:2096:36: note: expanded from macro '_ASM_SET_VIRT'
#define _ASM_SET_VIRT ".set\tvirt\n\t"
                                   ^
<inline asm>:4:2: note: instantiated into assembly here
        tlbgp
        ^
In file included from arch/mips/kvm/tlb.c:13:
In file included from ./include/linux/sched.h:12:
In file included from ./arch/mips/include/generated/asm/current.h:1:
In file included from ./include/asm-generic/current.h:5:
In file included from ./include/linux/thread_info.h:27:
In file included from ./include/linux/bitops.h:33:
In file included from ./arch/mips/include/asm/bitops.h:19:
In file included from ./arch/mips/include/asm/barrier.h:11:
In file included from ./arch/mips/include/asm/addrspace.h:13:
In file included from ./arch/mips/include/asm/mach-loongson64/spaces.h:16:
In file included from ./arch/mips/include/asm/mach-generic/spaces.h:15:
./arch/mips/include/asm/mipsregs.h:2841:3: error: instruction requires a CPU feature not currently enabled
                __tlbgr()
                ^
./arch/mips/include/asm/mipsregs.h:2107:19: note: expanded from macro '__tlbgr'
#define __tlbgr()       _ASM_SET_VIRT "tlbgr\n\t"
                        ^
./arch/mips/include/asm/mipsregs.h:2096:36: note: expanded from macro '_ASM_SET_VIRT'
#define _ASM_SET_VIRT ".set\tvirt\n\t"
                                   ^
<inline asm>:4:2: note: instantiated into assembly here
        tlbgr
        ^
In file included from arch/mips/kvm/tlb.c:13:
(deleted many lines)

LLVM is 13. This can be reproduced by

#!/bin/sh

KVER=5.16-rc3
LANG=C.UTF-8
export LANG
cd /var/tmp/tmp11mips64el_2

  cat >/tmp/config$$.txt <<EOF
CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT=n
CONFIG_KASAN=n
CONFIG_GCOV_KERNEL=n
CONFIG_COMPILE_TEST=n
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n
CONFIG_INIT_STACK_ALL_ZERO=y
CONFIG_KVM=y
CONFIG_PREEMPT=y
CONFIG_PREEMPT_DYNAMIC=y

CONFIG_WERROR=n
CONFIG_RUNTIME_TESTING_MENU=n
CONFIG_XFS_FS=n
CONFIG_OVERLAY_FS=n
CONFIG_EMBEDDED=n

CONFIG_ACPI=y
CONFIG_EFI_STUB=y
CONFIG_EFI=y
CONFIG_DMI=y
CONFIG_NUMA=y
CONFIG_MEMORY_HOTPLUG=y
CONFIG_HOTPLUG_PCI=y
CONFIG_HOTPLUG_PCI_PCIE=y
CONFIG_HOTPLUG_CPU=y

CONFIG_CPU_LITTLE_ENDIAN=y
CONFIG_CPU_BIG_ENDIAN=n
CONFIG_32BIT=n
CONFIG_64BIT=y
CONFIG_MACH_LOONGSON64=y
CONFIG_CPU_LOONGSON64=y
CONFIG_LOONGSON3_ENHANCEMENT=y
EOF


for a in mips; do
  rm -rf /var/tmp/tmp11mips64el_2/$a
  mkdir /var/tmp/tmp11mips64el_2/$a
  cd /var/tmp/tmp11mips64el_2/$a
  exec </dev/null >build-log-${KVER}-${a}.txt 2>&1
  set -xe
  tar zxf /var/tmp/linux-${KVER}.tar.gz
  cd linux-${KVER}

  cp /tmp/config$$.txt .config
  make LLVM=1 LLVM_IAS=1 CROSS_COMPILE=mips64el-linux-gnuabi64- allmodconfig
  cat /tmp/config$$.txt >>.config

  yes '' |
    chrt --idle 0 nice -19 make --keep-going ARCH=$a LLVM=1 LLVM_IAS=1 CROSS_COMPILE=mips64el-linux-gnuabi64- all &
  exec </dev/null >/dev/null 2>&1
done 
wait

[nathanchance]

I am going to make this issue about the first issue. I'll file a separate issue for the second one.

It seems that GAS accepts slti <reg>, <immediate> as shorthand for slti <reg>, <reg>, <immediate>:

$ cat head.s
 .macro smp_slave_setup
 slti $12, 0
 .endm
   smp_slave_setup

$ clang --target=mips64el-linux-gnu -mabi=64 -mips64r2 -c head.s
<instantiation>:1:11: error: invalid operand for instruction
slti $12, 0
          ^
head.s:4:4: note: while in macro instantiation
   smp_slave_setup
   ^

$ mips-suse-linux-gcc -EL -mabi=64 -mips64r2 -c head.s

$ mips-suse-linux-objdump -d head.o

head.o:     file format elf64-tradlittlemips


Disassembly of section .text:

0000000000000000 <.text>:
   0:   298c0000        slti    t0,t0,0
        ...

This can either be fixed in the kernel by using the full form (i.e., change slti t0, ... to slti t0, t0, ...) or in LLVM to match GAS. Judging from the rest of the kernel, changing it to the full form should not problematic and this has happened for other architectures such as PowerPC: https://git.kernel.org/linus/fef071be57dc43679a32d5b0e6ee176d6f12e9f2

I'll send a patch for this. @emojifreak I like to give reported by credits whenever possible, do you have a name and email that I can use for that? If not, no worries, as I will include a link to this issue with the initial report.

[emojifreak]

I'll send a patch for this. @emojifreak I like to give reported by credits whenever possible, do you have a name and email that I can use for that? If not, no worries, as I will include a link to this issue with the initial report.

@nathanchance Thank you. Please use
Name: Ryutaroh Matsumoto
email: ryutaroh@ict.e.titech.ac.jp

[nathanchance]

Thank you! Patch submitted: https://lore.kernel.org/r/20211207170129.578089-1-nathan@kernel.org/

[nathanchance]

I think it is worth requesting that LLVM support slti <reg>, <imm> so that this does not come up again.

[nathanchance]

Patch accepted: https://git.kernel.org/mips/c/f2c6c22fa83ab2577619009057b3ebcb5305bb03

[nathanchance]

Merged into mainline: https://git.kernel.org/linus/f2c6c22fa83ab2577619009057b3ebcb5305bb03