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Subject[RFC V3 07/18] objtool: Introduce INSN_UNKNOWN type
Date
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@arm.com>
---
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 723600aae13f..f3f94e2a1403 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -26,7 +26,8 @@
#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 3172f49c3a58..cba1d91451cc 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1952,6 +1952,13 @@ 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);
@@ -2383,7 +2390,8 @@ 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
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