[RFC][PATCH 11/16] objtool: Optimize find_symbol_by_name()

Peter Zijlstra
2020-03-12T13:52:32Z

Perf showed that find_symbol_by_name() takes time; add a symbol name
hash.

This shaves another second off of objtool on vmlinux.o runtime, down
to 15 seconds.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/elf.c | 10 +++++-----
tools/objtool/elf.h | 2 ++
2 files changed, 7 insertions(+), 5 deletions(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -134,13 +134,11 @@ struct symbol *find_symbol_by_offset(str

struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
{
- struct section *sec;
struct symbol *sym;

- list_for_each_entry(sec, &elf->sections, list)
- list_for_each_entry(sym, &sec->symbol_list, list)
- if (!strcmp(sym->name, name))
- return sym;
+ hash_for_each_possible(elf->symbol_name_hash, sym, name_hash, str_hash(name))
+ if (!strcmp(sym->name, name))
+ return sym;

return NULL;
}
@@ -365,6 +363,7 @@ static int read_symbols(struct elf *elf)
list_add(&sym->list, entry);

hash_add(elf->symbol_hash, &sym->hash, sym->idx);
+ hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name));
}

if (stats)
@@ -503,6 +502,7 @@ struct elf *elf_read(const char *name, i
memset(elf, 0, sizeof(*elf));

hash_init(elf->symbol_hash);
+ hash_init(elf->symbol_name_hash);
hash_init(elf->section_hash);
hash_init(elf->section_name_hash);
INIT_LIST_HEAD(&elf->sections);
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -47,6 +47,7 @@ struct symbol {
struct list_head list;
struct rb_node node;
struct hlist_node hash;
+ struct hlist_node name_hash;
GElf_Sym sym;
struct section *sec;
char *name;
@@ -77,6 +78,7 @@ struct elf {
char *name;
struct list_head sections;
DECLARE_HASHTABLE(symbol_hash, 20);
+ DECLARE_HASHTABLE(symbol_name_hash, 20);
DECLARE_HASHTABLE(section_hash, 16);
DECLARE_HASHTABLE(section_name_hash, 16);
};