Hi Andrew,
It's probably a bug fix that unveils the link errors.
tree: git://git.cmpxchg.org/linux-mmotm.git master
head: 8276ddb3c638602509386f1a05f75326dbf5ce09
commit: a5997ae6388f4071938c46951882823c3c39c9ee [195/211] x86-atomic-move-__atomic_add_unless-out-of-line-fix
config: um-x86_64_defconfig (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
git checkout a5997ae6388f4071938c46951882823c3c39c9ee
# save the attached .config to linux build tree
make ARCH=um SUBARCH=x86_64
All errors (new ones prefixed by >>):
kernel/built-in.o: In function `__atomic_add_unless':
>> include/asm-generic/atomic-instrumented.h:70: undefined reference to `__arch_atomic_add_unless'
>> include/asm-generic/atomic-instrumented.h:70: undefined reference to `__arch_atomic_add_unless'
>> include/asm-generic/atomic-instrumented.h:70: undefined reference to `__arch_atomic_add_unless'
>> include/asm-generic/atomic-instrumented.h:70: undefined reference to `__arch_atomic_add_unless'
>> include/asm-generic/atomic-instrumented.h:70: undefined reference to `__arch_atomic_add_unless'
mm/built-in.o:include/asm-generic/atomic-instrumented.h:70: more undefined references to `__arch_atomic_add_unless' follow
collect2: error: ld returned 1 exit status
vim +70 include/asm-generic/atomic-instrumented.h
64369b2e Dmitry Vyukov 2017-03-17 64 return arch_atomic64_cmpxchg(v, old, new);
64369b2e Dmitry Vyukov 2017-03-17 65 }
64369b2e Dmitry Vyukov 2017-03-17 66
64369b2e Dmitry Vyukov 2017-03-17 67 static __always_inline int __atomic_add_unless(atomic_t *v, int a, int u)
64369b2e Dmitry Vyukov 2017-03-17 68 {
867c3290 Dmitry Vyukov 2017-03-17 69 kasan_check_write(v, sizeof(*v));
64369b2e Dmitry Vyukov 2017-03-17 @70 return __arch_atomic_add_unless(v, a, u);
64369b2e Dmitry Vyukov 2017-03-17 71 }
64369b2e Dmitry Vyukov 2017-03-17 72
64369b2e Dmitry Vyukov 2017-03-17 73
:::::: The code at line 70 was first introduced by commit
:::::: 64369b2ed11177f1e9ae3f5901041f77c2c20f10 asm-generic, x86: wrap atomic operations
:::::: TO: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
:::::: CC: Johannes Weiner <hannes@xxxxxxxxxxx>
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