[RFC v5 31/57] objtool: arm64: Decode load/store with register offset

[Julien Thierry]

Decode load/store instruction using the value of a register as offset
for the target address.

Since objtool can't keep track of the possible values of this offset, it
is not possible to take this instructions into account for stack frame
validation. Luckily, the compiler does not tend to generate these
instructions for stack/frame pointer manipulation.

Suggested-by: Raphael Gault <raphael.gault@xxxxxxx>
Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/arm64/decode.c             | 34 +++++++++++++++++++
 .../objtool/arch/arm64/include/insn_decode.h  |  3 ++
 2 files changed, 37 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index 7064302416f4..00d5d627af08 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -830,6 +830,11 @@ static struct aarch64_insn_decoder ld_st_decoder[] = {
 		.value = 0b001100000000011,
 		.decode_func = arm_decode_ld_st_imm_pre,
 	},
+	{
+		.mask = 0b001101010000011,
+		.value = 0b001100010000010,
+		.decode_func = arm_decode_ld_st_regs_off,
+	},
 	{
 		.mask = 0b001101000000000,
 		.value = 0b001101000000000,
@@ -1200,3 +1205,32 @@ int arm_decode_ld_st_imm_unpriv(u32 instr, enum insn_type *type,
 	}
 	return 0;
 }
+
+int arm_decode_ld_st_regs_off(u32 instr, enum insn_type *type,
+			      unsigned long *immediate,
+			      struct list_head *ops_list)
+{
+	unsigned char size = 0, V = 0, opc = 0, option = 0;
+	unsigned char decode_field = 0;
+
+	size = (instr >> 30) & ONES(2);
+	V = EXTRACT_BIT(instr, 26);
+	opc = (instr >> 22) & ONES(2);
+	option = (instr >> 13) & ONES(3);
+
+#define LD_ROFF_UNALLOC_1	0b01110
+#define LD_ROFF_UNALLOC_2	0b10110
+#define LD_ROFF_UNALLOC_3	0b10011
+	decode_field = (size << 3) | (V << 2) | opc;
+	if (!EXTRACT_BIT(option, 1) ||
+	    (decode_field & LD_ROFF_UNALLOC_1) == LD_ROFF_UNALLOC_1 ||
+	    (decode_field & LD_ROFF_UNALLOC_2) == LD_ROFF_UNALLOC_2 ||
+	    (decode_field & 0b10111) == LD_ROFF_UNALLOC_3) {
+		return arm_decode_unknown(instr, type, immediate, ops_list);
+	}
+#undef LD_ROFF_UNALLOC_1
+#undef LD_ROFF_UNALLOC_2
+#undef LD_ROFF_UNALLOC_3
+
+	return 0;
+}
diff --git a/tools/objtool/arch/arm64/include/insn_decode.h b/tools/objtool/arch/arm64/include/insn_decode.h
index 1e031b12cf69..9043ca6f6708 100644
--- a/tools/objtool/arch/arm64/include/insn_decode.h
+++ b/tools/objtool/arch/arm64/include/insn_decode.h
@@ -106,6 +106,9 @@ int arm_decode_ld_st_imm_unpriv(u32 instr, enum insn_type *type,
 int arm_decode_ld_st_imm_pre(u32 instr, enum insn_type *type,
 			     unsigned long *immediate,
 			     struct list_head *ops_list);
+int arm_decode_ld_st_regs_off(u32 instr, enum insn_type *type,
+			      unsigned long *immediate,
+			      struct list_head *ops_list);
 int arm_decode_ld_st_regs_unsigned(u32 instr, enum insn_type *type,
 				   unsigned long *immediate,
 				   struct list_head *ops_list);
-- 
2.21.0