[RFC v5 24/57] objtool: arm64: Decode system instructions not affecting the flow

[Julien Thierry]

Decode basic system instructions that do not cause jumps or stack
pointer modifications.

Suggested-by: Raphael Gault <raphael.gault@xxxxxxx>
Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/arm64/decode.c             | 95 +++++++++++++++++++
 .../objtool/arch/arm64/include/insn_decode.h  | 23 +++++
 2 files changed, 118 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index a30c3294cc21..c38d73fb57e1 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -87,6 +87,7 @@ static arm_decode_class aarch64_insn_class_decode_table[NR_INSN_CLASS] = {
 	[INSN_UNKNOWN]			= arm_decode_unknown,
 	[INSN_UNALLOC]			= arm_decode_unknown,
 	[0b1000 ... INSN_DP_IMM]	= arm_decode_dp_imm,
+	[0b1010 ... INSN_SYS_BRANCH]	= arm_decode_br_sys,
 };
 
 /*
@@ -391,3 +392,97 @@ int arm_decode_extract(u32 instr, enum insn_type *type,
 
 	return arm_decode_unknown(instr, type, immediate, ops_list);
 }
+
+static struct aarch64_insn_decoder br_sys_decoder[] = {
+	{
+		.mask = 0b1111111111111111111111,
+		.value = 0b1100100000011001011111,
+		.decode_func = arm_decode_hints,
+	},
+	{
+		.mask = 0b1111111111111111100000,
+		.value = 0b1100100000011001100000,
+		.decode_func = arm_decode_barriers,
+	},
+	{
+		.mask = 0b1111111111000111100000,
+		.value = 0b1100100000000010000000,
+		.decode_func = arm_decode_pstate,
+	},
+	{
+		.mask = 0b1111111011000000000000,
+		.value = 0b1100100001000000000000,
+		.decode_func = arm_decode_system_insn,
+	},
+	{
+		.mask = 0b1111111010000000000000,
+		.value = 0b1100100010000000000000,
+		.decode_func = arm_decode_system_regs,
+	},
+};
+
+int arm_decode_br_sys(u32 instr, enum insn_type *type,
+		      unsigned long *immediate, struct list_head *ops_list)
+{
+	u32 decode_field = 0, op1 = 0;
+	unsigned char op0 = 0, op2 = 0;
+	int i = 0;
+
+	op0 = (instr >> 29) & ONES(3);
+	op1 = (instr >> 12) & ONES(14);
+	op2 = instr & ONES(5);
+
+	decode_field = op0;
+	decode_field = (decode_field << 19) | (op1 << 5) | op2;
+
+	for (i = 0; i < ARRAY_SIZE(br_sys_decoder); i++) {
+		if ((decode_field & br_sys_decoder[i].mask) ==
+		    br_sys_decoder[i].value) {
+			return br_sys_decoder[i].decode_func(instr,
+							     type,
+							     immediate,
+							     ops_list);
+		}
+	}
+
+	return arm_decode_unknown(instr, type, immediate, ops_list);
+}
+
+int arm_decode_hints(u32 instr, enum insn_type *type,
+		     unsigned long *immediate, struct list_head *ops_list)
+{
+	*type = INSN_NOP;
+	return 0;
+}
+
+int arm_decode_barriers(u32 instr, enum insn_type *type,
+			unsigned long *immediate, struct list_head *ops_list)
+{
+	/* TODO:check unallocated */
+	*type = INSN_OTHER;
+	return 0;
+}
+
+int arm_decode_pstate(u32 instr, enum insn_type *type,
+		      unsigned long *immediate, struct list_head *ops_list)
+{
+	/* TODO:check unallocated */
+	*type = INSN_OTHER;
+	return 0;
+}
+
+int arm_decode_system_insn(u32 instr, enum insn_type *type,
+			   unsigned long *immediate, struct list_head *ops_list)
+{
+	/* TODO:check unallocated */
+	*type = INSN_OTHER;
+	return 0;
+}
+
+int arm_decode_system_regs(u32 instr, enum insn_type *type,
+			   unsigned long *immediate, struct list_head *ops_list)
+{
+	/* TODO:check unallocated */
+	*type = INSN_OTHER;
+	return 0;
+}
diff --git a/tools/objtool/arch/arm64/include/insn_decode.h b/tools/objtool/arch/arm64/include/insn_decode.h
index 6f68e8887cdb..777a62f1a141 100644
--- a/tools/objtool/arch/arm64/include/insn_decode.h
+++ b/tools/objtool/arch/arm64/include/insn_decode.h
@@ -9,6 +9,7 @@
 #define INSN_UNKNOWN	0b0001
 #define INSN_UNALLOC	0b0011
 #define INSN_DP_IMM	0b1001	//0x100x
+#define INSN_SYS_BRANCH	0b1011	//0x101x
 
 #define NR_INSN_CLASS	16
 #define INSN_CLASS(opcode)	(((opcode) >> 25) & (NR_INSN_CLASS - 1))
@@ -25,9 +26,17 @@ typedef int (*arm_decode_class)(u32 instr, enum insn_type *type,
 				unsigned long *immediate,
 				struct list_head *ops_list);
 
+struct aarch64_insn_decoder {
+	u32 mask;
+	u32 value;
+	arm_decode_class decode_func;
+};
+
 /* arm64 instruction classes */
 int arm_decode_dp_imm(u32 instr, enum insn_type *type,
 		      unsigned long *immediate, struct list_head *ops_list);
+int arm_decode_br_sys(u32 instr, enum insn_type *type,
+		      unsigned long *immediate, struct list_head *ops_list);
 int arm_decode_unknown(u32 instr, enum insn_type *type,
 		       unsigned long *immediate, struct list_head *ops_list);
 
@@ -47,4 +56,18 @@ int arm_decode_bitfield(u32 instr, enum insn_type *type,
 			unsigned long *immediate, struct list_head *ops_list);
 int arm_decode_extract(u32 instr, enum insn_type *type,
 		       unsigned long *immediate, struct list_head *ops_list);
+
+/* arm64 branch, exception generation, system insn subclasses */
+int arm_decode_hints(u32 instr, enum insn_type *type,
+		     unsigned long *immediate, struct list_head *ops_list);
+int arm_decode_barriers(u32 instr, enum insn_type *type,
+			unsigned long *immediate, struct list_head *ops_list);
+int arm_decode_pstate(u32 instr, enum insn_type *type,
+		      unsigned long *immediate, struct list_head *ops_list);
+int arm_decode_system_insn(u32 instr, enum insn_type *type,
+			   unsigned long *immediate,
+			   struct list_head *ops_list);
+int arm_decode_system_regs(u32 instr, enum insn_type *type,
+			   unsigned long *immediate,
+			   struct list_head *ops_list);
 #endif /* _ARM_INSN_DECODE_H */
-- 
2.21.0