linux-kernel - [PATCH] MIPS: bpf: Fix uninitialised target compiler error

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Date:   Wed, 27 Sep 2017 09:14:58 +0100
From:   Matt Redfearn <matt.redfearn@...tec.com>
To:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <james.hogan@...tec.com>
CC:     <linux-mips@...ux-mips.org>, David Daney <david.daney@...ium.com>,
        Matt Redfearn <matt.redfearn@...tec.com>,
        "# v4 . 13+" <stable@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Colin Ian King <colin.king@...onical.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH] MIPS: bpf: Fix uninitialised target compiler error

Compiling ebpf_jit.c with gcc 4.9 results in a (likely spurious)
compiler warning, as gcc has detected that the variable "target" may be
used uninitialised. Since -Werror is active, this is treated as an error
and causes a kernel build failure whenever CONFIG_MIPS_EBPF_JIT is
enabled.

arch/mips/net/ebpf_jit.c: In function 'build_one_insn':
arch/mips/net/ebpf_jit.c:1118:80: error: 'target' may be used
uninitialized in this function [-Werror=maybe-uninitialized]
    emit_instr(ctx, j, target);
                                                                                ^
cc1: all warnings being treated as errors

Fix this by initialising "target" to 0. If it really is used
uninitialised this would result in a jump to 0 and a detectable run time
failure.

Signed-off-by: Matt Redfearn <matt.redfearn@...tec.com>
Fixes: b6bd53f9c4e8 ("MIPS: Add missing file for eBPF JIT.")
Cc: <stable@...r.kernel.org> # v4.13+
---

 arch/mips/net/ebpf_jit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 7646891c4e9b..01b7a87ea678 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -667,7 +667,7 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 {
 	int src, dst, r, td, ts, mem_off, b_off;
 	bool need_swap, did_move, cmp_eq;
-	unsigned int target;
+	unsigned int target = 0;
 	u64 t64;
 	s64 t64s;
 	int bpf_op = BPF_OP(insn->code);
-- 
2.7.4