[question] kernel build fails with O0 gcc optimization flag

[Yury Norov]

Hi all.

I changed optimization from O2 to O0 in Makefile:
        609 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
        610 KBUILD_CFLAGS   += -Os $(call cc-disable-warning,maybe-uninitialized,)
        611 else
        612 KBUILD_CFLAGS   += -O2 <-- here
        613 endif

And broke the build. O1 looks fine.

I tried Ubuntu and Cavium GCC:
        gcc version 5.2.1 20151010 (Ubuntu 5.2.1-22ubuntu1) 
        gcc version 5.2.0 (Cavium Development Version) 

Kernel is v4.3, defconfig, ARCH=arm64.

What am I doing wrong?

BR,
Yury.

[...]
  CC      arch/arm64/kernel/debug-monitors.o
In file included from include/linux/ioport.h:12:0,
                 from include/linux/device.h:16,
                 from include/linux/node.h:17,
                 from include/linux/cpu.h:16,
                 from arch/arm64/kernel/debug-monitors.c:21:
In function ‘__percpu_add’,
    inlined from ‘enable_debug_monitors’ at arch/arm64/kernel/debug-monitors.c:91:6:
include/linux/compiler.h:492:38: error: call to ‘__compiletime_assert_97’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
include/linux/compiler.h:475:4: note: in definition of macro ‘__compiletime_assert’ prefix ## suffix();    \
    ^
include/linux/compiler.h:492:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^
include/linux/bug.h:84:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^
./arch/arm64/include/asm/percpu.h:91:3: note: in expansion of macro ‘BUILD_BUG’
   BUILD_BUG();      \
   ^
./arch/arm64/include/asm/percpu.h:97:1: note: in expansion of macro ‘PERCPU_OP’
 PERCPU_OP(add, add)
 ^
In function ‘__percpu_add’,
    inlined from ‘enable_debug_monitors’ at arch/arm64/kernel/debug-monitors.c:95:6:
include/linux/compiler.h:492:38: error: call to ‘__compiletime_assert_97’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
include/linux/compiler.h:475:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^
include/linux/compiler.h:492:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^
include/linux/bug.h:84:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^
./arch/arm64/include/asm/percpu.h:91:3: note: in expansion of macro ‘BUILD_BUG’
   BUILD_BUG();      \
   ^
./arch/arm64/include/asm/percpu.h:97:1: note: in expansion of macro ‘PERCPU_OP’
 PERCPU_OP(add, add)
 ^
In function ‘__percpu_add’,
    inlined from ‘disable_debug_monitors’ at arch/arm64/kernel/debug-monitors.c:111:6:
include/linux/compiler.h:492:38: error: call to ‘__compiletime_assert_97’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
include/linux/compiler.h:475:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^
include/linux/compiler.h:492:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^
include/linux/bug.h:84:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^
./arch/arm64/include/asm/percpu.h:91:3: note: in expansion of macro ‘BUILD_BUG’
   BUILD_BUG();      \
   ^
./arch/arm64/include/asm/percpu.h:97:1: note: in expansion of macro ‘PERCPU_OP’
 PERCPU_OP(add, add)
 ^
In function ‘__percpu_add’,
    inlined from ‘disable_debug_monitors’ at arch/arm64/kernel/debug-monitors.c:115:6:
include/linux/compiler.h:492:38: error: call to ‘__compiletime_assert_97’ declared with attribute error: BUILD_BUG failed
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
include/linux/compiler.h:475:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^
include/linux/compiler.h:492:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^
include/linux/bug.h:84:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
                     ^
./arch/arm64/include/asm/percpu.h:91:3: note: in expansion of macro ‘BUILD_BUG’
   BUILD_BUG();      \
   ^
./arch/arm64/include/asm/percpu.h:97:1: note: in expansion of macro ‘PERCPU_OP’
 PERCPU_OP(add, add)
 ^
In function ‘__list_add_rcu’,
    inlined from ‘list_add_rcu’ at include/linux/rculist.h:80:2,
    inlined from ‘register_break_hook’ at arch/arm64/kernel/debug-monitors.c:279:2:
include/linux/compiler.h:492:38: error: call to ‘__compiletime_assert_54’ declared with attribute error: Need native word sized stores/loads for atomicity.
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
include/linux/compiler.h:475:4: note: in definition of macro ‘__compiletime_assert’
    prefix ## suffix();    \
    ^
include/linux/compiler.h:492:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^
include/linux/compiler.h:495:2: note: in expansion of macro ‘compiletime_assert’
  compiletime_assert(__native_word(t),    \
  ^
./arch/arm64/include/asm/barrier.h:44:2: note: in expansion of macro ‘compiletime_assert_atomic_type’
  compiletime_assert_atomic_type(*p);    \
  ^
include/linux/rcupdate.h:677:34: note: in expansion of macro ‘smp_store_release’
 #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
                                  ^
include/linux/rculist.h:54:2: note: in expansion of macro ‘rcu_assign_pointer’
  rcu_assign_pointer(list_next_rcu(prev), new);
  ^
scripts/Makefile.build:258: recipe for target 'arch/arm64/kernel/debug-monitors.o' failed
make[1]: *** [arch/arm64/kernel/debug-monitors.o] Error 1
Makefile:941: recipe for target 'arch/arm64/kernel' failed
make: *** [arch/arm64/kernel] Error 2