[RFC][PATCH 07/16] objtool: Optimize find_section_by_index()

Peter Zijlstra
2020-03-12T13:51:46Z

In order to avoid a linear search (over 20k entries), add an
section_hash to the elf object.

This reduces objtool on vmlinux.o from a few minutes to around 45
seconds.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/elf.c | 7 ++++++-
tools/objtool/elf.h | 2 ++
2 files changed, 8 insertions(+), 1 deletion(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -38,7 +38,7 @@ static struct section *find_section_by_i
{
struct section *sec;

- list_for_each_entry(sec, &elf->sections, list)
+ hash_for_each_possible(elf->section_hash, sec, hash, idx)
if (sec->idx == idx)
return sec;

@@ -191,6 +191,8 @@ static int read_sections(struct elf *elf
}
}
sec->len = sec->sh.sh_size;
+
+ hash_add(elf->section_hash, &sec->hash, sec->idx);
}

if (stats)
@@ -430,6 +432,7 @@ struct elf *elf_read(const char *name, i
memset(elf, 0, sizeof(*elf));

hash_init(elf->symbol_hash);
+ hash_init(elf->section_hash);
INIT_LIST_HEAD(&elf->sections);

elf->fd = open(name, flags);
@@ -570,6 +573,8 @@ struct section *elf_create_section(struc
shstrtab->len += strlen(name) + 1;
shstrtab->changed = true;

+ hash_add(elf->section_hash, &sec->hash, sec->idx);
+
return sec;
}

--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -25,6 +25,7 @@

struct section {
struct list_head list;
+ struct hlist_node hash;
GElf_Shdr sh;
struct list_head symbol_list;
struct list_head rela_list;
@@ -71,6 +72,7 @@ struct elf {
char *name;
struct list_head sections;
DECLARE_HASHTABLE(symbol_hash, 20);
+ DECLARE_HASHTABLE(section_hash, 16);
};