objtool: Optimize find_section_by_index()

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>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.381249993@infradead.org

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index ff29306..9007713 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -38,7 +38,7 @@ static struct section *find_section_by_index(struct elf *elf,
 {
        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;
 
@@ -166,8 +166,6 @@ static int read_sections(struct elf *elf)
                INIT_LIST_HEAD(&sec->rela_list);
                hash_init(sec->rela_hash);
 
-               list_add_tail(&sec->list, &elf->sections);
-
                s = elf_getscn(elf->elf, i);
                if (!s) {
                        WARN_ELF("elf_getscn");
@@ -201,6 +199,9 @@ static int read_sections(struct elf *elf)
                        }
                }
                sec->len = sec->sh.sh_size;
+
+               list_add_tail(&sec->list, &elf->sections);
+               hash_add(elf->section_hash, &sec->hash, sec->idx);
        }
 
        if (stats)
@@ -439,6 +440,7 @@ struct elf *elf_read(const char *name, int flags)
        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);
@@ -501,8 +503,6 @@ struct section *elf_create_section(struct elf *elf, const char *name,
        INIT_LIST_HEAD(&sec->rela_list);
        hash_init(sec->rela_hash);
 
-       list_add_tail(&sec->list, &elf->sections);
-
        s = elf_newscn(elf->elf);
        if (!s) {
                WARN_ELF("elf_newscn");
@@ -579,6 +579,9 @@ struct section *elf_create_section(struct elf *elf, const char *name,
        shstrtab->len += strlen(name) + 1;
        shstrtab->changed = true;
 
+       list_add_tail(&sec->list, &elf->sections);
+       hash_add(elf->section_hash, &sec->hash, sec->idx);
+
        return sec;
 }
 

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 1222980..8c272eb 100644 (file)
--- 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);
 };