[RFC][PATCH 05/16] objtool: Optimize find_symbol_by_index()

[Peter Zijlstra]

The symbol index is object wide, not per section, so it makes no sense
to have the symbol_hash be part of the section object. By moving it to
the elf object we avoid the linear sections iteration.

This reduces the runtime of objtool on vmlinux.o from over 3 hours (I
gave up) to a few minutes. The defconfig vmlinux.o has around 20k
sections.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 tools/objtool/elf.c |   14 ++++++--------
 tools/objtool/elf.h |    3 +--
 2 files changed, 7 insertions(+), 10 deletions(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -46,13 +46,11 @@ static struct section *find_section_by_i
 
 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 {
-	struct section *sec;
 	struct symbol *sym;
 
-	list_for_each_entry(sec, &elf->sections, list)
-		hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
-			if (sym->idx == idx)
-				return sym;
+	hash_for_each_possible(elf->symbol_hash, sym, hash, idx)
+		if (sym->idx == idx)
+			return sym;
 
 	return NULL;
 }
@@ -156,7 +154,6 @@ static int read_sections(struct elf *elf
 		INIT_LIST_HEAD(&sec->symbol_list);
 		INIT_LIST_HEAD(&sec->rela_list);
 		hash_init(sec->rela_hash);
-		hash_init(sec->symbol_hash);
 
 		list_add_tail(&sec->list, &elf->sections);
 
@@ -289,7 +286,8 @@ static int read_symbols(struct elf *elf)
 		}
 		sym->alias = alias;
 		list_add(&sym->list, entry);
-		hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
+
+		hash_add(elf->symbol_hash, &sym->hash, sym->idx);
 	}
 
 	/* Create parent/child links for any cold subfunctions */
@@ -415,6 +413,7 @@ struct elf *elf_read(const char *name, i
 	}
 	memset(elf, 0, sizeof(*elf));
 
+	hash_init(elf->symbol_hash);
 	INIT_LIST_HEAD(&elf->sections);
 
 	elf->fd = open(name, flags);
@@ -476,7 +475,6 @@ struct section *elf_create_section(struc
 	INIT_LIST_HEAD(&sec->symbol_list);
 	INIT_LIST_HEAD(&sec->rela_list);
 	hash_init(sec->rela_hash);
-	hash_init(sec->symbol_hash);
 
 	list_add_tail(&sec->list, &elf->sections);
 
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -27,7 +27,6 @@ struct section {
 	struct list_head list;
 	GElf_Shdr sh;
 	struct list_head symbol_list;
-	DECLARE_HASHTABLE(symbol_hash, 8);
 	struct list_head rela_list;
 	DECLARE_HASHTABLE(rela_hash, 16);
 	struct section *base, *rela;
@@ -71,7 +70,7 @@ struct elf {
 	int fd;
 	char *name;
 	struct list_head sections;
-	DECLARE_HASHTABLE(rela_hash, 16);
+	DECLARE_HASHTABLE(symbol_hash, 20);
 };