linux-kernel - [tip:x86/mm 7/9] arch/x86/include/asm/mwait.h:30:15: error: invalid operand for instruction

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Message-ID: <202504030802.2lEVBSpN-lkp@intel.com>
Date: Thu, 3 Apr 2025 08:12:34 +0800
From: kernel test robot <lkp@...el.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: [tip:x86/mm 7/9] arch/x86/include/asm/mwait.h:30:15: error: invalid
 operand for instruction

Hi Uros,

FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/mm
head:   6c921984e75c78e1c509d99b8cde04f1eadd46fb
commit: cd3b85b27542968198e3d588a2bc0591930ee2ee [7/9] x86/idle: Use MONITOR and MWAIT mnemonics in <asm/mwait.h>
config: x86_64-buildonly-randconfig-003-20250403 (https://download.01.org/0day-ci/archive/20250403/202504030802.2lEVBSpN-lkp@intel.com/config)
compiler: clang version 20.1.1 (https://github.com/llvm/llvm-project 424c2d9b7e4de40d0804dd374721e6411c27d1d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250403/202504030802.2lEVBSpN-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202504030802.2lEVBSpN-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from arch/x86/kernel/process.c:36:
>> arch/x86/include/asm/mwait.h:30:15: error: invalid operand for instruction
      30 |         asm volatile("monitor %0, %1, %2" :: "a" (eax), "c" (ecx), "d" (edx));
         |                      ^
   <inline asm>:1:16: note: instantiated into assembly here
       1 |         monitor %rax, %ecx, %edx
         |                       ^~~~~
   In file included from arch/x86/kernel/process.c:36:
>> arch/x86/include/asm/mwait.h:95:15: error: instruction requires: Not 64-bit mode
      95 |         asm volatile("sti; mwait %0, %1" :: "a" (eax), "c" (ecx));
         |                      ^
   <inline asm>:1:7: note: instantiated into assembly here
       1 |         sti; mwait %eax, %ecx
         |              ^
   2 errors generated.


vim +30 arch/x86/include/asm/mwait.h

    27	
    28	static __always_inline void __monitor(const void *eax, u32 ecx, u32 edx)
    29	{
  > 30		asm volatile("monitor %0, %1, %2" :: "a" (eax), "c" (ecx), "d" (edx));
    31	}
    32	
    33	static __always_inline void __monitorx(const void *eax, u32 ecx, u32 edx)
    34	{
    35		/* "monitorx %eax, %ecx, %edx;" */
    36		asm volatile(".byte 0x0f, 0x01, 0xfa;"
    37			     :: "a" (eax), "c" (ecx), "d"(edx));
    38	}
    39	
    40	static __always_inline void __mwait(u32 eax, u32 ecx)
    41	{
    42		mds_idle_clear_cpu_buffers();
    43	
    44		asm volatile("mwait %0, %1" :: "a" (eax), "c" (ecx));
    45	}
    46	
    47	/*
    48	 * MWAITX allows for a timer expiration to get the core out a wait state in
    49	 * addition to the default MWAIT exit condition of a store appearing at a
    50	 * monitored virtual address.
    51	 *
    52	 * Registers:
    53	 *
    54	 * MWAITX ECX[1]: enable timer if set
    55	 * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0
    56	 * frequency is the same as the TSC frequency.
    57	 *
    58	 * Below is a comparison between MWAIT and MWAITX on AMD processors:
    59	 *
    60	 *                 MWAIT                           MWAITX
    61	 * opcode          0f 01 c9           |            0f 01 fb
    62	 * ECX[0]                  value of RFLAGS.IF seen by instruction
    63	 * ECX[1]          unused/#GP if set  |            enable timer if set
    64	 * ECX[31:2]                     unused/#GP if set
    65	 * EAX                           unused (reserve for hint)
    66	 * EBX[31:0]       unused             |            max wait time (P0 clocks)
    67	 *
    68	 *                 MONITOR                         MONITORX
    69	 * opcode          0f 01 c8           |            0f 01 fa
    70	 * EAX                     (logical) address to monitor
    71	 * ECX                     #GP if not zero
    72	 */
    73	static __always_inline void __mwaitx(u32 eax, u32 ebx, u32 ecx)
    74	{
    75		/* No MDS buffer clear as this is AMD/HYGON only */
    76	
    77		/* "mwaitx %eax, %ebx, %ecx;" */
    78		asm volatile(".byte 0x0f, 0x01, 0xfb;"
    79			     :: "a" (eax), "b" (ebx), "c" (ecx));
    80	}
    81	
    82	/*
    83	 * Re-enable interrupts right upon calling mwait in such a way that
    84	 * no interrupt can fire _before_ the execution of mwait, ie: no
    85	 * instruction must be placed between "sti" and "mwait".
    86	 *
    87	 * This is necessary because if an interrupt queues a timer before
    88	 * executing mwait, it would otherwise go unnoticed and the next tick
    89	 * would not be reprogrammed accordingly before mwait ever wakes up.
    90	 */
    91	static __always_inline void __sti_mwait(u32 eax, u32 ecx)
    92	{
    93		mds_idle_clear_cpu_buffers();
    94	
  > 95		asm volatile("sti; mwait %0, %1" :: "a" (eax), "c" (ecx));
    96	}
    97	

-- 
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https://github.com/intel/lkp-tests/wiki