bpf, x64: save few bytes when mul is in alu32

Add a generic emit_mov_reg() helper in order to reuse it in BPF
multiplication to load the src into rax, we can save a few bytes
in alu32 while doing so.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/x86/net/bpf_jit_comp.c

@@ -422,6 +422,24 @@ static void emit_mov_imm64(u8 **pprog, u32 dst_reg,
 	*pprog = prog;
 }
 
+static void emit_mov_reg(u8 **pprog, bool is64, u32 dst_reg, u32 src_reg)
+{
+	u8 *prog = *pprog;
+	int cnt = 0;
+
+	if (is64) {
+		/* mov dst, src */
+		EMIT_mov(dst_reg, src_reg);
+	} else {
+		/* mov32 dst, src */
+		if (is_ereg(dst_reg) || is_ereg(src_reg))
+			EMIT1(add_2mod(0x40, dst_reg, src_reg));
+		EMIT2(0x89, add_2reg(0xC0, dst_reg, src_reg));
+	}
+
+	*pprog = prog;
+}
+
 static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		  int oldproglen, struct jit_context *ctx)
 {
@@ -480,16 +498,11 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
 			break;
 
-			/* mov dst, src */
 		case BPF_ALU64 | BPF_MOV | BPF_X:
-			EMIT_mov(dst_reg, src_reg);
-			break;
-
-			/* mov32 dst, src */
 		case BPF_ALU | BPF_MOV | BPF_X:
-			if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, dst_reg, src_reg));
-			EMIT2(0x89, add_2reg(0xC0, dst_reg, src_reg));
+			emit_mov_reg(&prog,
+				     BPF_CLASS(insn->code) == BPF_ALU64,
+				     dst_reg, src_reg);
 			break;
 
 			/* neg dst */
@@ -615,6 +628,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_ALU | BPF_MUL | BPF_X:
 		case BPF_ALU64 | BPF_MUL | BPF_K:
 		case BPF_ALU64 | BPF_MUL | BPF_X:
+		{
+			bool is64 = BPF_CLASS(insn->code) == BPF_ALU64;
+
 			if (dst_reg != BPF_REG_0)
 				EMIT1(0x50); /* push rax */
 			if (dst_reg != BPF_REG_3)
@@ -624,14 +640,11 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			EMIT_mov(AUX_REG, dst_reg);
 
 			if (BPF_SRC(insn->code) == BPF_X)
-				/* mov rax, src_reg */
-				EMIT_mov(BPF_REG_0, src_reg);
+				emit_mov_reg(&prog, is64, BPF_REG_0, src_reg);
 			else
-				/* mov rax, imm32 */
-				emit_mov_imm32(&prog, true,
-					       BPF_REG_0, imm32);
+				emit_mov_imm32(&prog, is64, BPF_REG_0, imm32);
 
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
+			if (is64)
 				EMIT1(add_1mod(0x48, AUX_REG));
 			else if (is_ereg(AUX_REG))
 				EMIT1(add_1mod(0x40, AUX_REG));
@@ -646,7 +659,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 				EMIT1(0x58); /* pop rax */
 			}
 			break;
-
+		}
 			/* shifts */
 		case BPF_ALU | BPF_LSH | BPF_K:
 		case BPF_ALU | BPF_RSH | BPF_K: