[RFC PATCH 09/17] objtool: arm64: Decode LDR instructions

[Julien Thierry]

Load literal instructions can generate constants inside code sections.
Record the locations of the constants in order to be able to remove
their corresponding "struct instruction".

Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
---
 tools/objtool/arch/arm64/decode.c    | 86 ++++++++++++++++++++++++++++
 tools/objtool/arch/x86/decode.c      |  5 ++
 tools/objtool/check.c                |  3 +
 tools/objtool/include/objtool/arch.h |  3 +
 4 files changed, 97 insertions(+)

diff --git a/tools/objtool/arch/arm64/decode.c b/tools/objtool/arch/arm64/decode.c
index 1087ede67bcd..b4d4d5b051b0 100644
--- a/tools/objtool/arch/arm64/decode.c
+++ b/tools/objtool/arch/arm64/decode.c
@@ -30,6 +30,73 @@ static unsigned long sign_extend(unsigned long x, int nbits)
 	return ((~0UL + (sign_bit ^ 1)) << nbits) | x;
 }
 
+struct insn_loc {
+	const struct section *sec;
+	unsigned long offset;
+	struct hlist_node hnode;
+	bool ignorable;
+};
+
+DEFINE_HASHTABLE(invalid_insns, 16);
+
+static int record_invalid_insn(const struct section *sec,
+			       unsigned long offset,
+			       bool ignore)
+{
+	struct insn_loc *loc;
+	struct hlist_head *l;
+
+	l = &invalid_insns[hash_min(offset, HASH_BITS(invalid_insns))];
+	if (!hlist_empty(l)) {
+		loc = hlist_entry(l->first, struct insn_loc, hnode);
+		loc->ignorable |= ignore;
+		return 0;
+	}
+
+	loc = malloc(sizeof(*loc));
+	if (!loc) {
+		WARN("malloc failed");
+		return -1;
+	}
+
+	loc->sec = sec;
+	loc->offset = offset;
+	loc->ignorable = ignore;
+
+	hash_add(invalid_insns, &loc->hnode, loc->offset);
+
+	return 0;
+}
+
+int arch_post_process_instructions(struct objtool_file *file)
+{
+	struct hlist_node *tmp;
+	struct insn_loc *loc;
+	unsigned int bkt;
+	int res = 0;
+
+	hash_for_each_safe(invalid_insns, bkt, tmp, loc, hnode) {
+		struct instruction *insn;
+
+		insn = find_insn(file, (struct section *) loc->sec, loc->offset);
+		if (insn) {
+			if (loc->ignorable) {
+				list_del(&insn->list);
+				hash_del(&insn->hash);
+				free(insn);
+			} else {
+				WARN_FUNC("can't decode instruction", insn->sec, insn->offset);
+				return -1;
+			}
+		}
+
+		hash_del(&loc->hnode);
+		free(loc);
+	}
+
+	return res;
+}
+
 bool arch_callee_saved_reg(unsigned char reg)
 {
 	switch (reg) {
@@ -359,6 +426,25 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 	case AARCH64_INSN_CLS_LDST:
 		if (arm_decode_load_store(insn, type, immediate, ops_list))
 			break;
+		if (aarch64_insn_is_ldr_lit(insn)) {
+			long pc_offset;
+
+			pc_offset = insn & GENMASK(23, 5);
+			/* Sign extend and multiply by 4 */
+			pc_offset = (pc_offset << (64 - 23));
+			pc_offset = ((pc_offset >> (64 - 23)) >> 5) << 2;
+
+			if (record_invalid_insn(sec, offset + pc_offset, true))
+				return -1;
+
+			/* 64-bit literal */
+			if (insn & BIT(30)) {
+				if (record_invalid_insn(sec,
+							offset + pc_offset + 4,
+							true))
+					return -1;
+			}
+		}
 		*type = INSN_OTHER;
 		break;
 	default:
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 6baa22732ca6..e76d987ce3c7 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -549,6 +549,11 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 	return 0;
 }
 
+int arch_post_process_instructions(struct objtool_file *file)
+{
+	return 0;
+}
+
 void arch_initial_func_cfi_state(struct cfi_init_state *state)
 {
 	int i;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 270b507e7098..d902697a388e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -319,6 +319,9 @@ static int decode_instructions(struct objtool_file *file)
 	if (stats)
 		printf("nr_insns: %lu\n", nr_insns);
 
+	if (arch_post_process_instructions(file))
+		return -1;
+
 	return 0;
 
 err:
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 6ff0685f5cc5..456d0465b676 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -66,6 +66,7 @@ struct stack_op {
 	struct list_head list;
 };
 
+struct objtool_file;
 struct instruction;
 
 void arch_initial_func_cfi_state(struct cfi_init_state *state);
@@ -76,6 +77,8 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 			    unsigned long *immediate,
 			    struct list_head *ops_list);
 
+int arch_post_process_instructions(struct objtool_file *file);
+
 bool arch_callee_saved_reg(unsigned char reg);
 
 unsigned long arch_jump_destination(struct instruction *insn);
-- 
2.25.4