[PATCH 3/3] objtool: optimize add_dead_ends for split sections

[Sami Tolvanen]

When running objtool on vmlinux.o compiled with -ffunction-sections,
.rela.discard.(un)reachable often contains relocations that point to
a different section. Instead of iterating through the list of all
instructions each time, store a pointer to the last instruction of
each section when decoding instructions.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
---
 tools/objtool/check.c | 43 ++++++++++++++++++++++++++-----------------
 tools/objtool/check.h |  4 ++++
 tools/objtool/elf.h   |  1 +
 3 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4770fb07b365..7d4104de0a5e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -237,6 +237,7 @@ static void clear_insn_state(struct insn_state *state)
 static int decode_instructions(struct objtool_file *file)
 {
 	struct section *sec;
+	struct section_info *sec_info = NULL;
 	struct symbol *func;
 	unsigned long offset;
 	struct instruction *insn;
@@ -253,6 +254,8 @@ static int decode_instructions(struct objtool_file *file)
 		    strncmp(sec->name, ".discard.", 9))
 			sec->text = true;
 
+		insn = NULL;
+
 		for (offset = 0; offset < sec->len; offset += insn->len) {
 			insn = malloc(sizeof(*insn));
 			if (!insn) {
@@ -279,6 +282,17 @@ static int decode_instructions(struct objtool_file *file)
 			nr_insns++;
 		}
 
+		if (insn) {
+			sec_info = malloc(sizeof(*sec_info));
+			if (!sec_info) {
+				WARN("malloc failed");
+				return -1;
+			}
+
+			sec_info->last_insn = insn;
+			sec->section_info = sec_info;
+		}
+
 		list_for_each_entry(func, &sec->symbol_list, list) {
 			if (func->type != STT_FUNC || func->alias != func)
 				continue;
@@ -312,7 +326,6 @@ static int add_dead_ends(struct objtool_file *file)
 	struct section *sec;
 	struct rela *rela;
 	struct instruction *insn;
-	bool found;
 
 	/*
 	 * By default, "ud2" is a dead end unless otherwise annotated, because
@@ -338,15 +351,13 @@ static int add_dead_ends(struct objtool_file *file)
 		if (insn)
 			insn = list_prev_entry(insn, list);
 		else if (rela->addend == rela->sym->sec->len) {
-			found = false;
-			list_for_each_entry_reverse(insn, &file->insn_list, list) {
-				if (insn->sec == rela->sym->sec) {
-					found = true;
-					break;
-				}
-			}
+			struct section_info *sec_info = (struct section_info *)
+				rela->sym->sec->section_info;
+
+			if (sec_info)
+				insn = sec_info->last_insn;
 
-			if (!found) {
+			if (!insn) {
 				WARN("can't find unreachable insn at %s+0x%x",
 				     rela->sym->sec->name, rela->addend);
 				return -1;
@@ -380,15 +391,13 @@ static int add_dead_ends(struct objtool_file *file)
 		if (insn)
 			insn = list_prev_entry(insn, list);
 		else if (rela->addend == rela->sym->sec->len) {
-			found = false;
-			list_for_each_entry_reverse(insn, &file->insn_list, list) {
-				if (insn->sec == rela->sym->sec) {
-					found = true;
-					break;
-				}
-			}
+			struct section_info *sec_info = (struct section_info *)
+				rela->sym->sec->section_info;
+
+			if (sec_info)
+				insn = sec_info->last_insn;
 
-			if (!found) {
+			if (!insn) {
 				WARN("can't find reachable insn at %s+0x%x",
 				     rela->sym->sec->name, rela->addend);
 				return -1;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index bc78eca7982e..353677ec85d4 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -47,6 +47,10 @@ struct instruction {
 	struct orc_entry orc;
 };
 
+struct section_info {
+	struct instruction *last_insn;
+};
+
 struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index ebbb10c61e24..98f2b41d18e4 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -40,6 +40,7 @@ struct section {
 	int idx;
 	unsigned int len;
 	bool changed, text, rodata;
+	void *section_info;
 };
 
 struct symbol {
-- 
2.26.1.301.g55bc3eb7cb9-goog