| Message ID | 20190417072121.4450-1-natechancellor@gmail.com (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Commit | ff8acf929014b7f87315588e0daf8597c8aa9d1c |
| Headers | show |
| Series | arm64: futex: Restore oldval initialization to work around buggy compilers | expand |
On Wed, Apr 17, 2019 at 12:21:21AM -0700, Nathan Chancellor wrote: > Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with > non-zero result value") removed oldval's zero initialization in > arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, > Android's arm64 GCC 4.9.4 [1] does not agree: > > ../kernel/futex.c: In function 'do_futex': > ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized > in this function [-Wmaybe-uninitialized] > return oldval == cmparg; > ^ > In file included from ../kernel/futex.c:73:0: > ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here > int oldval, ret, tmp; > ^ > > GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser > returns right away, avoiding the uninitialized use that it claims. > Restoring the zero initialization works around this issue. > > [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ > > Cc: stable@vger.kernel.org > Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
On Wed, Apr 17, 2019 at 12:21:21AM -0700, Nathan Chancellor wrote: > Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with > non-zero result value") removed oldval's zero initialization in > arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, > Android's arm64 GCC 4.9.4 [1] does not agree: > > ../kernel/futex.c: In function 'do_futex': > ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized > in this function [-Wmaybe-uninitialized] > return oldval == cmparg; > ^ > In file included from ../kernel/futex.c:73:0: > ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here > int oldval, ret, tmp; > ^ > > GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser > returns right away, avoiding the uninitialized use that it claims. > Restoring the zero initialization works around this issue. > > [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ > > Cc: stable@vger.kernel.org > Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Thanks. That compiler version doesn't seem very smart. I'll queue this for -rc6.
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h index e1d95f08f8e1..c7e1a7837706 100644 --- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -50,7 +50,7 @@ do { \ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *_uaddr) { - int oldval, ret, tmp; + int oldval = 0, ret, tmp; u32 __user *uaddr = __uaccess_mask_ptr(_uaddr); pagefault_disable();
Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") removed oldval's zero initialization in arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, Android's arm64 GCC 4.9.4 [1] does not agree: ../kernel/futex.c: In function 'do_futex': ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized] return oldval == cmparg; ^ In file included from ../kernel/futex.c:73:0: ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here int oldval, ret, tmp; ^ GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser returns right away, avoiding the uninitialized use that it claims. Restoring the zero initialization works around this issue. [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ Cc: stable@vger.kernel.org Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> --- arch/arm64/include/asm/futex.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)