[RFC v5 29/57] objtool: arm64: Decode branch to register instruction

[Julien Thierry]

Decode instructions producing jumps in the execution flow, taking the
value of their operand register as the target address.

Return instructions are just branch to register instruction with
the link register (x31) as implicit operand.

Suggested-by: Raphael Gault <raphael.gault@xxxxxxx>
Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/arm64/decode.c             | 150 ++++++++++++++++++
 .../objtool/arch/arm64/include/insn_decode.h  |   3 +
 2 files changed, 153 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index 7986ded8b622..bf9334451b40 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -444,6 +444,11 @@ static struct aarch64_insn_decoder br_sys_decoder[] = {
 		.value = 0b0011000000000000000000,
 		.decode_func = arm_decode_br_tst_imm,
 	},
+	{
+		.mask = 0b1111000000000000000000,
+		.value = 0b1101000000000000000000,
+		.decode_func = arm_decode_br_uncond_reg,
+	},
 };
 
 int arm_decode_br_sys(u32 instr, enum insn_type *type,
@@ -654,3 +659,148 @@ int arm_decode_br_tst_imm(u32 instr, enum insn_type *type,
 	*type = INSN_JUMP_CONDITIONAL;
 	return 0;
 }
+
+static struct aarch64_insn_decoder ret_decoder[] = {
+	/*
+	 * RET, RETAA, RETAB
+	 */
+	{
+		.mask = 0b1111111111111110000011111,
+		.value = 0b0010111110000000000000000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111111111111111,
+		.value = 0b0010111110000101111111111,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111111111111111,
+		.value = 0b0010111110000111111111111,
+		.decode_func = NULL,
+	},
+};
+
+static struct aarch64_insn_decoder br_decoder[] = {
+	/*
+	 * BR, BRAA, BRAAZ, BRAB, BRABZ
+	 */
+	{
+		.mask = 0b1111111111111110000011111,
+		.value = 0b0000111110000000000000000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000011111,
+		.value = 0b0000111110000100000011111,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000011111,
+		.value = 0b0000111110000110000011111,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000000000,
+		.value = 0b1000111110000100000000000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000000000,
+		.value = 0b1000111110000110000000000,
+		.decode_func = NULL,
+	},
+};
+
+#define INSN_DRPS_FIELD		0b0101111110000001111100000
+#define INSN_DRPS_MASK		0b1111111111111111111111111
+
+static struct aarch64_insn_decoder ct_sw_decoder[] = {
+	/*
+	 * ERET, ERETAA, ERETAB
+	 */
+	{
+		.mask = INSN_DRPS_MASK,
+		.value = 0b0100111110000001111100000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = INSN_DRPS_MASK,
+		.value = 0b0100111110000101111111111,
+		.decode_func = NULL,
+	},
+	{
+		.mask = INSN_DRPS_MASK,
+		.value = 0b0100111110000111111111111,
+		.decode_func = NULL,
+	},
+};
+
+static struct aarch64_insn_decoder call_decoder[] = {
+	/*
+	 * BLR, BLRAA, BLRAAZ, BLRAB, BLRABZ
+	 */
+	{
+		.mask = 0b1111111111111110000011111,
+		.value =  0b0001111110000000000000000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000011111,
+		.value = 0b0001111110000100000011111,
+		.decode_func = NULL,
+	},
+	{
+		0b1111111111111110000011111,
+		0b0001111110000110000011111,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000000000,
+		.value = 0b1001111110000100000000000,
+		.decode_func = NULL,
+	},
+	{
+		.mask = 0b1111111111111110000000000,
+		.value = 0b1001111110000110000000000,
+		.decode_func = NULL,
+	},
+};
+
+int arm_decode_br_uncond_reg(u32 instr, enum insn_type *type,
+			     unsigned long *immediate,
+			     struct list_head *ops_list)
+{
+	u32 decode_field = 0;
+	int i = 0;
+
+	decode_field = instr & ONES(25);
+	*type = 0;
+	for (i = 0; i < ARRAY_SIZE(br_decoder); i++) {
+		if ((decode_field & br_decoder[i].mask) == br_decoder[i].value)
+			*type = INSN_JUMP_DYNAMIC;
+	}
+	for (i = 0; i < ARRAY_SIZE(call_decoder); i++) {
+		if ((decode_field & call_decoder[i].value) ==
+		    call_decoder[i].value)
+			*type = INSN_CALL_DYNAMIC;
+	}
+	for (i = 0; i < ARRAY_SIZE(ret_decoder); i++) {
+		if ((decode_field & ret_decoder[i].mask) ==
+		    ret_decoder[i].value)
+			*type = INSN_RETURN;
+	}
+	for (i = 0; i < ARRAY_SIZE(ct_sw_decoder); i++) {
+		if ((decode_field & ct_sw_decoder[i].mask) ==
+		    ct_sw_decoder[i].value)
+			*type = INSN_CONTEXT_SWITCH;
+	}
+	if ((decode_field & INSN_DRPS_MASK) == INSN_DRPS_FIELD)
+		*type = INSN_OTHER;
+	if (*type == 0)
+		return arm_decode_unknown(instr, type, immediate, ops_list);
+	return 0;
+}
+
+#undef INSN_DRPS_FIELD
+#undef INSN_DRPS_MASK
diff --git a/tools/objtool/arch/arm64/include/insn_decode.h b/tools/objtool/arch/arm64/include/insn_decode.h
index ceb80a58c548..6e600f408bea 100644
--- a/tools/objtool/arch/arm64/include/insn_decode.h
+++ b/tools/objtool/arch/arm64/include/insn_decode.h
@@ -83,4 +83,7 @@ int arm_decode_br_tst_imm(u32 instr, enum insn_type *type,
 int arm_decode_br_cond_imm(u32 instr, enum insn_type *type,
 			   unsigned long *immediate,
 			   struct list_head *ops_list);
+int arm_decode_br_uncond_reg(u32 instr, enum insn_type *type,
+			     unsigned long *immediate,
+			     struct list_head *ops_list);
 #endif /* _ARM_INSN_DECODE_H */
-- 
2.21.0