[RFC v5 25/57] objtool: arm64: Decode calls to higher EL

[Julien Thierry]

Decode instructions that volontarily trigger exceptions to a higher
exception level.

It is assumed that the higher exception level should service the request
in a sane maner, returning to the caller exception level without
altering its context too much (e.g. not modifying the PC, the stack
pointer or the frame pointer).

Suggested-by: Raphael Gault <raphael.gault@xxxxxxx>
Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/arm64/decode.c             | 45 +++++++++++++++++++
 .../objtool/arch/arm64/include/insn_decode.h  |  2 +
 2 files changed, 47 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index c38d73fb57e1..aa00de725686 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -419,6 +419,11 @@ static struct aarch64_insn_decoder br_sys_decoder[] = {
 		.value = 0b1100100010000000000000,
 		.decode_func = arm_decode_system_regs,
 	},
+	{
+		.mask = 0b1111100000000000000000,
+		.value = 0b1100000000000000000000,
+		.decode_func = arm_decode_except_gen,
+	},
 };
 
 int arm_decode_br_sys(u32 instr, enum insn_type *type,
@@ -486,3 +491,43 @@ int arm_decode_system_regs(u32 instr, enum insn_type *type,
 	*type = INSN_OTHER;
 	return 0;
 }
+
+int arm_decode_except_gen(u32 instr, enum insn_type *type,
+			  unsigned long *immediate, struct list_head *ops_list)
+{
+	u32 imm16 = 0;
+	unsigned char opc = 0, op2 = 0, LL = 0, decode_field = 0;
+
+	imm16 = (instr >> 5) & ONES(16);
+	opc = (instr >> 21) & ONES(3);
+	op2 = (instr >> 2) & ONES(3);
+	LL = instr & ONES(2);
+	decode_field = (opc << 5) | (op2 << 2) | LL;
+
+#define INSN_SVC	0b00000001
+#define INSN_HVC	0b00000010
+#define INSN_SMC	0b00000011
+
+	switch (decode_field) {
+	case INSN_SVC:
+	case INSN_HVC:
+	case INSN_SMC:
+		/*
+		 * We consider that the context will be restored correctly
+		 * with an unchanged sp and the same general registers
+		 */
+		*type = INSN_NOP;
+		return 0;
+	default:
+		return arm_decode_unknown(instr, type, immediate, ops_list);
+	}
+
+#undef INSN_SVC
+#undef INSN_HVC
+#undef INSN_SMC
+#undef INSN_BRK
+#undef INSN_HLT
+#undef INSN_DCPS1
+#undef INSN_DCPS2
+#undef INSN_DCPS3
+}
diff --git a/tools/objtool/arch/arm64/include/insn_decode.h b/tools/objtool/arch/arm64/include/insn_decode.h
index 777a62f1a141..a55dcbfcfed2 100644
--- a/tools/objtool/arch/arm64/include/insn_decode.h
+++ b/tools/objtool/arch/arm64/include/insn_decode.h
@@ -70,4 +70,6 @@ int arm_decode_system_insn(u32 instr, enum insn_type *type,
 int arm_decode_system_regs(u32 instr, enum insn_type *type,
 			   unsigned long *immediate,
 			   struct list_head *ops_list);
+int arm_decode_except_gen(u32 instr, enum insn_type *type,
+			  unsigned long *immediate, struct list_head *ops_list);
 #endif /* _ARM_INSN_DECODE_H */
-- 
2.21.0