Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 17 Apr 2019 10:53:37 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers |
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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.
-- Catalin
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