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objtool: Optimize find_section_by_name() 

In order to avoid yet another linear search of (20k) sections, add a
name based hash.

This reduces objtool runtime on vmlinux.o by some 10s to around 35s.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.440174280@infradead.org
This commit is contained in:
Peter Zijlstra 2020-03-12 09:32:10 +01:00
parent 5303899687
commit ae358196fa
2 changed files with 12 additions and 1 deletions
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10
tools/objtool/elf.c
View File

@ -22,11 +22,16 @@
#define MAX_NAME_LEN 128
static inline u32 str_hash(const char *str)
{
return jhash(str, strlen(str), 0);
}
struct section *find_section_by_name(struct elf *elf, const char *name)
{
struct section *sec;
list_for_each_entry(sec, &elf->sections, list)
hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
if (!strcmp(sec->name, name))
return sec;
@ -202,6 +207,7 @@ static int read_sections(struct elf *elf)
list_add_tail(&sec->list, &elf->sections);
hash_add(elf->section_hash, &sec->hash, sec->idx);
hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
}
if (stats)
@ -441,6 +447,7 @@ struct elf *elf_read(const char *name, int flags)
hash_init(elf->symbol_hash);
hash_init(elf->section_hash);
hash_init(elf->section_name_hash);
INIT_LIST_HEAD(&elf->sections);
elf->fd = open(name, flags);
@ -581,6 +588,7 @@ struct section *elf_create_section(struct elf *elf, const char *name,
list_add_tail(&sec->list, &elf->sections);
hash_add(elf->section_hash, &sec->hash, sec->idx);
hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
return sec;
}

3
tools/objtool/elf.h
View File

@ -10,6 +10,7 @@
#include <gelf.h>
#include <linux/list.h>
#include <linux/hashtable.h>
#include <linux/jhash.h>
#ifdef LIBELF_USE_DEPRECATED
# define elf_getshdrnum elf_getshnum
@ -26,6 +27,7 @@
struct section {
struct list_head list;
struct hlist_node hash;
struct hlist_node name_hash;
GElf_Shdr sh;
struct list_head symbol_list;
struct list_head rela_list;
@ -73,6 +75,7 @@ struct elf {
struct list_head sections;
DECLARE_HASHTABLE(symbol_hash, 20);
DECLARE_HASHTABLE(section_hash, 16);
DECLARE_HASHTABLE(section_name_hash, 16);
};