bpf, x64: Factor out emission of REX byte in more cases

Introduce a single reg version of maybe_emit_mod() and factor out
common code in more cases.
Signed-off-by: Jie Meng <jmeng@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211006194135.608932-1-jmeng@fb.com

arch/x86/net/bpf_jit_comp.c

@@ -721,6 +721,20 @@ static void maybe_emit_mod(u8 **pprog, u32 dst_reg, u32 src_reg, bool is64)
 	*pprog = prog;
 }
 
+/*
+ * Similar version of maybe_emit_mod() for a single register
+ */
+static void maybe_emit_1mod(u8 **pprog, u32 reg, bool is64)
+{
+	u8 *prog = *pprog;
+
+	if (is64)
+		EMIT1(add_1mod(0x48, reg));
+	else if (is_ereg(reg))
+		EMIT1(add_1mod(0x40, reg));
+	*pprog = prog;
+}
+
 /* LDX: dst_reg = *(u8*)(src_reg + off) */
 static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
 {
@@ -951,10 +965,8 @@ 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));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_ALU64);
 			EMIT2(0xF7, add_1reg(0xD8, dst_reg));
 			break;
 
@@ -968,10 +980,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_ALU64 | BPF_AND | BPF_K:
 		case BPF_ALU64 | BPF_OR | BPF_K:
 		case BPF_ALU64 | BPF_XOR | BPF_K:
-			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));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_ALU64);
 
 			/*
 			 * b3 holds 'normal' opcode, b2 short form only valid
@@ -1059,11 +1069,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			 */
 			EMIT2(0x31, 0xd2);
 
-			if (is64)
-				EMIT1(add_1mod(0x48, src_reg));
-			else if (is_ereg(src_reg))
-				EMIT1(add_1mod(0x40, src_reg));
 			/* div src_reg */
+			maybe_emit_1mod(&prog, src_reg, is64);
 			EMIT2(0xF7, add_1reg(0xF0, src_reg));
 
 			if (BPF_OP(insn->code) == BPF_MOD &&
@@ -1084,10 +1091,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 
 		case BPF_ALU | BPF_MUL | BPF_K:
 		case BPF_ALU64 | BPF_MUL | BPF_K:
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_2mod(0x48, dst_reg, dst_reg));
-			else if (is_ereg(dst_reg))
-				EMIT1(add_2mod(0x40, dst_reg, dst_reg));
+			maybe_emit_mod(&prog, dst_reg, dst_reg,
+				       BPF_CLASS(insn->code) == BPF_ALU64);
 
 			if (is_imm8(imm32))
 				/* imul dst_reg, dst_reg, imm8 */
@@ -1102,10 +1107,8 @@ 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_X:
-			if (BPF_CLASS(insn->code) == BPF_ALU64)
-				EMIT1(add_2mod(0x48, src_reg, dst_reg));
-			else if (is_ereg(dst_reg) || is_ereg(src_reg))
-				EMIT1(add_2mod(0x40, src_reg, dst_reg));
+			maybe_emit_mod(&prog, src_reg, dst_reg,
+				       BPF_CLASS(insn->code) == BPF_ALU64);
 
 			/* imul dst_reg, src_reg */
 			EMIT3(0x0F, 0xAF, add_2reg(0xC0, src_reg, dst_reg));
@@ -1118,10 +1121,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 		case BPF_ALU64 | BPF_LSH | BPF_K:
 		case BPF_ALU64 | BPF_RSH | BPF_K:
 		case BPF_ALU64 | BPF_ARSH | BPF_K:
-			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));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_ALU64);
 
 			b3 = simple_alu_opcodes[BPF_OP(insn->code)];
 			if (imm32 == 1)
@@ -1152,10 +1153,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			}
 
 			/* shl %rax, %cl | shr %rax, %cl | sar %rax, %cl */
-			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));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_ALU64);
 
 			b3 = simple_alu_opcodes[BPF_OP(insn->code)];
 			EMIT2(0xD3, add_1reg(b3, dst_reg));
@@ -1465,10 +1464,8 @@ st:			if (is_imm8(insn->off))
 		case BPF_JMP | BPF_JSET | BPF_K:
 		case BPF_JMP32 | BPF_JSET | BPF_K:
 			/* test dst_reg, imm32 */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_1mod(0x48, dst_reg));
-			else if (is_ereg(dst_reg))
-				EMIT1(add_1mod(0x40, dst_reg));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_JMP);
 			EMIT2_off32(0xF7, add_1reg(0xC0, dst_reg), imm32);
 			goto emit_cond_jmp;
 
@@ -1501,10 +1498,8 @@ st:			if (is_imm8(insn->off))
 			}
 
 			/* cmp dst_reg, imm8/32 */
-			if (BPF_CLASS(insn->code) == BPF_JMP)
-				EMIT1(add_1mod(0x48, dst_reg));
-			else if (is_ereg(dst_reg))
-				EMIT1(add_1mod(0x40, dst_reg));
+			maybe_emit_1mod(&prog, dst_reg,
+					BPF_CLASS(insn->code) == BPF_JMP);
 
 			if (is_imm8(imm32))
 				EMIT3(0x83, add_1reg(0xF8, dst_reg), imm32);