linux-kernel - [rcu:rcu/next 30/45] include/linux/compiler.h:343:2: error: implicit declaration of function 'smp_read_barrier

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Date:   Sun, 15 Oct 2017 07:29:36 +0800
From:   kbuild test robot <fengguang.wu@...el.com>
To:     Will Deacon <will.deacon@....com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [rcu:rcu/next 30/45] include/linux/compiler.h:343:2: error: implicit
 declaration of function 'smp_read_barrier_depends'

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/next
head:   ea788e7da4886dff9782ad61d4c5e6ebadfa8260
commit: c3a030152f67ef977129c11e5b37a8e6071d4b6f [30/45] locking/barriers: Kill lockless_dereference
config: sparc-alldefconfig (attached as .config)
compiler: sparc-linux-gcc (GCC) 6.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout c3a030152f67ef977129c11e5b37a8e6071d4b6f
        # save the attached .config to linux build tree
        make.cross ARCH=sparc 

All errors (new ones prefixed by >>):

   In file included from include/uapi/linux/stddef.h:1:0,
                    from include/linux/stddef.h:4,
                    from include/uapi/linux/posix_types.h:4,
                    from include/uapi/linux/types.h:13,
                    from include/linux/types.h:5,
                    from include/linux/thread_info.h:10,
                    from arch/sparc/include/asm/current.h:14,
                    from include/linux/sched.h:11,
                    from arch/sparc/kernel/asm-offsets.c:13:
   include/linux/list.h: In function 'list_empty':
>> include/linux/compiler.h:343:2: error: implicit declaration of function 'smp_read_barrier_depends' [-Werror=implicit-function-declaration]
     smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
     ^
   include/linux/compiler.h:346:22: note: in expansion of macro '__READ_ONCE'
    #define READ_ONCE(x) __READ_ONCE(x, 1)
                         ^~~~~~~~~~~
   include/linux/list.h:202:9: note: in expansion of macro 'READ_ONCE'
     return READ_ONCE(head->next) == head;
            ^~~~~~~~~
   cc1: some warnings being treated as errors
   make[2]: *** [arch/sparc/kernel/asm-offsets.s] Error 1
   make[2]: Target '__build' not remade because of errors.
   make[1]: *** [prepare0] Error 2
   make[1]: Target 'prepare' not remade because of errors.
   make: *** [sub-make] Error 2

vim +/smp_read_barrier_depends +343 include/linux/compiler.h

   312	
   313	/*
   314	 * Prevent the compiler from merging or refetching reads or writes. The
   315	 * compiler is also forbidden from reordering successive instances of
   316	 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
   317	 * compiler is aware of some particular ordering.  One way to make the
   318	 * compiler aware of ordering is to put the two invocations of READ_ONCE,
   319	 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
   320	 *
   321	 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
   322	 * data types like structs or unions. If the size of the accessed data
   323	 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
   324	 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy(). There's at
   325	 * least two memcpy()s: one for the __builtin_memcpy() and then one for
   326	 * the macro doing the copy of variable - '__u' allocated on the stack.
   327	 *
   328	 * Their two major use cases are: (1) Mediating communication between
   329	 * process-level code and irq/NMI handlers, all running on the same CPU,
   330	 * and (2) Ensuring that the compiler does not  fold, spindle, or otherwise
   331	 * mutilate accesses that either do not require ordering or that interact
   332	 * with an explicit memory barrier or atomic instruction that provides the
   333	 * required ordering.
   334	 */
   335	
   336	#define __READ_ONCE(x, check)						\
   337	({									\
   338		union { typeof(x) __val; char __c[1]; } __u;			\
   339		if (check)							\
   340			__read_once_size(&(x), __u.__c, sizeof(x));		\
   341		else								\
   342			__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
 > 343		smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
   344		__u.__val;							\
   345	})
   346	#define READ_ONCE(x) __READ_ONCE(x, 1)
   347	

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