From 334d683655a0a4a68792ab1de6b20f4b559b0fcd Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Wed, 17 Apr 2019 00:21:21 -0700 Subject: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers commit ff8acf929014b7f87315588e0daf8597c8aa9d1c upstream. 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") Reviewed-by: Greg Kroah-Hartman Signed-off-by: Nathan Chancellor Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/futex.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h index 66bc1ef344f9..f7fda38d7183 100644 --- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -50,7 +50,7 @@ futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) int cmp = (encoded_op >> 24) & 15; int oparg = (int)(encoded_op << 8) >> 20; int cmparg = (int)(encoded_op << 20) >> 20; - int oldval, ret, tmp; + int oldval = 0, ret, tmp; if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) oparg = 1U << (oparg & 0x1f); -- 2.21.0