[RFC 15/16] objtool: Introduce INSN_UNKNOWN type

[Raphael Gault]

On arm64 some object files contain data stored in the .text section.
This data is interpreted by objtool as instruction but can't be
identified as a valid one. In order to keep analysing those files we
introduce INSN_UNKNOWN type. The "unknown instruction" warning will thus
only be raised if such instructions are uncountered while validating an
execution branch.

This change doesn't impact the x86 decoding logic since 0 is still used
as a way to specify an unknown type, raising the "unknown instruction"
warning during the decoding phase still.

Signed-off-by: Raphael Gault <raphael.gault@xxxxxxx>
---
 tools/objtool/arch.h                           |  3 ++-
 tools/objtool/arch/arm64/decode.c              |  8 ++++----
 tools/objtool/arch/arm64/include/insn_decode.h |  4 ++--
 tools/objtool/check.c                          | 10 +++++++++-
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index c1ea6ecdd5d2..1f84690ad9f5 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -38,7 +38,8 @@
 #define INSN_CLAC		12
 #define INSN_STD		13
 #define INSN_CLD		14
-#define INSN_OTHER		15
+#define INSN_UNKNOWN		15
+#define INSN_OTHER		16
 #define INSN_LAST		INSN_OTHER
 
 enum op_dest_type {
diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index 5be1d87b1a1c..a40338a895f5 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -37,9 +37,9 @@
  */
 static arm_decode_class aarch64_insn_class_decode_table[] = {
 	[INSN_RESERVED]			= arm_decode_reserved,
-	[INSN_UNKNOWN]			= arm_decode_unknown,
+	[INSN_UNALLOC_1]		= arm_decode_unknown,
 	[INSN_SVE_ENC]			= arm_decode_sve_encoding,
-	[INSN_UNALLOC]			= arm_decode_unknown,
+	[INSN_UNALLOC_2]		= arm_decode_unknown,
 	[INSN_LD_ST_4]			= arm_decode_ld_st,
 	[INSN_DP_REG_5]			= arm_decode_dp_reg,
 	[INSN_LD_ST_6]			= arm_decode_ld_st,
@@ -191,7 +191,7 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 int arm_decode_unknown(u32 instr, unsigned char *type,
 		       unsigned long *immediate, struct stack_op *op)
 {
-	*type = 0;
+	*type = INSN_UNKNOWN;
 	return 0;
 }
 
@@ -206,7 +206,7 @@ int arm_decode_reserved(u32 instr, unsigned char *type,
 			unsigned long *immediate, struct stack_op *op)
 {
 	*immediate = instr & ONES(16);
-	*type = INSN_BUG;
+	*type = INSN_UNKNOWN;
 	return 0;
 }
 
diff --git a/tools/objtool/arch/arm64/include/insn_decode.h b/tools/objtool/arch/arm64/include/insn_decode.h
index eb54fc39dca5..a01d76306749 100644
--- a/tools/objtool/arch/arm64/include/insn_decode.h
+++ b/tools/objtool/arch/arm64/include/insn_decode.h
@@ -20,9 +20,9 @@
 #include "../../../arch.h"
 
 #define INSN_RESERVED	0b0000
-#define INSN_UNKNOWN	0b0001
+#define INSN_UNALLOC_1	0b0001
 #define INSN_SVE_ENC	0b0010
-#define INSN_UNALLOC	0b0011
+#define INSN_UNALLOC_2	0b0011
 #define INSN_DP_IMM	0b1001	//0x100x
 #define INSN_BRANCH	0b1011	//0x101x
 #define INSN_LD_ST_4	0b0100	//0bx1x0
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index bfb36cca9be1..90a26f238899 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1961,6 +1961,13 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 	while (1) {
 		next_insn = next_insn_same_sec(file, insn);
 
+		if (insn->type == INSN_UNKNOWN) {
+			WARN("%s+0x%lx unknown instruction type, should never be reached",
+			     insn->sec->name,
+			     insn->offset);
+			return 1;
+		}
+
 		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
 			WARN("%s() falls through to next function %s()",
 			     func->name, insn->func->name);
@@ -2391,7 +2398,8 @@ static int validate_reachable_instructions(struct objtool_file *file)
 		return 0;
 
 	for_each_insn(file, insn) {
-		if (insn->visited || ignore_unreachable_insn(insn))
+		if (insn->visited || ignore_unreachable_insn(insn) ||
+		    insn->type == INSN_UNKNOWN)
 			continue;
 
 		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
-- 
2.17.1