linux-kernel - [PATCH v2 bpf-next 03/13] bpf: x86: Factor out function to emit NEG

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Date:   Fri, 27 Nov 2020 17:57:28 +0000
From:   Brendan Jackman <jackmanb@...gle.com>
To:     bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        linux-kernel@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH v2 bpf-next 03/13] bpf: x86: Factor out function to emit NEG

There's currently only one usage of this but implementation of
atomic_sub add another.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 arch/x86/net/bpf_jit_comp.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a839c1a54276..49dea0c1a130 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -783,6 +783,22 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 	*pprog = prog;
 }
 
+
+static void emit_neg(u8 **pprog, u32 reg, bool is64)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	/* Emit REX byte if necessary */
+	if (is64)
+		EMIT1(add_1mod(0x48, reg));
+	else if (is_ereg(reg))
+		EMIT1(add_1mod(0x40, reg));
+
+	EMIT2(0xF7, add_1reg(0xD8, reg)); /* x86 NEG */
+	*pprog = prog;
+}
+
 static bool ex_handler_bpf(const struct exception_table_entry *x,
 			   struct pt_regs *regs, int trapnr,
 			   unsigned long error_code, unsigned long fault_addr)
@@ -884,11 +900,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			/* neg dst */
 		case BPF_ALU | BPF_NEG:
 		case BPF_ALU64 | BPF_NEG:
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_1mod(0x48, dst_reg));
-			else if (is_ereg(dst_reg))
-				EMIT1(add_1mod(0x40, dst_reg));
-			EMIT2(0xF7, add_1reg(0xD8, dst_reg));
+			emit_neg(&prog, dst_reg,
+				 BPF_CLASS(insn->code) == BPF_ALU64);
 			break;
 
 		case BPF_ALU | BPF_ADD | BPF_K:
-- 
2.29.2.454.gaff20da3a2-goog