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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