tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/pti.entry head: 6891282dd3ab7fead975ed52d0f7f8da37ab96a5 commit: c2bc66082e1048c7573d72e62f597bdc5ce13fea [10/39] locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE() config: h8300-h8300h-sim_defconfig (attached as .config) compiler: h8300-linux-gcc (GCC) 7.2.0 reproduce: wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross git checkout c2bc66082e1048c7573d72e62f597bdc5ce13fea # save the attached .config to linux build tree make.cross ARCH=h8300
All error/warnings (new ones prefixed by >>):
In file included from include/uapi/linux/stddef.h:2:0,
from include/linux/stddef.h:5,
from arch/h8300/kernel/asm-offsets.c:12:
include/linux/list.h: In function 'list_empty':
>> include/linux/compiler.h:344:2: 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:347:22: note: in expansion of macro '__READ_ONCE'
#define READ_ONCE(x) __READ_ONCE(x, 1)
^~~~~~~~~~~
>> include/linux/list.h:203:9: note: in expansion of macro 'READ_ONCE'
return READ_ONCE(head->next) == head;
^~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [arch/h8300/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 +344 include/linux/compiler.h
313
314 /*
315 * Prevent the compiler from merging or refetching reads or writes. The
316 * compiler is also forbidden from reordering successive instances of
317 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
318 * compiler is aware of some particular ordering. One way to make the
319 * compiler aware of ordering is to put the two invocations of
READ_ONCE,
320 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
321 *
322 * In contrast to ACCESS_ONCE these two macros will also work on
aggregate
323 * data types like structs or unions. If the size of the accessed data
324 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
325 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy(). There's at
326 * least two memcpy()s: one for the __builtin_memcpy() and then one for
327 * the macro doing the copy of variable - '__u' allocated on the stack.
328 *
329 * Their two major use cases are: (1) Mediating communication between
330 * process-level code and irq/NMI handlers, all running on the same CPU,
331 * and (2) Ensuring that the compiler does not fold, spindle, or
otherwise
332 * mutilate accesses that either do not require ordering or that
interact
333 * with an explicit memory barrier or atomic instruction that provides
the
334 * required ordering.
335 */
336
337 #define __READ_ONCE(x, check)
\
338 ({
\
339 union { typeof(x) __val; char __c[1]; } __u;
\
340 if (check)
\
341 __read_once_size(&(x), __u.__c, sizeof(x));
\
342 else
\
343 __read_once_size_nocheck(&(x), __u.__c, sizeof(x));
\
> 344 smp_read_barrier_depends(); /* Enforce dependency ordering from
> x */ \
345 __u.__val;
\
346 })
> 347 #define READ_ONCE(x) __READ_ONCE(x, 1)
348
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.config.gz
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