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

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 900771365ae3689fdeb4cdf623a6a99812ed021b..20fe40d5101d86615eed940a983a4189d1e4d60e 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -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;
 }

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 8c272eb515c82ab0221a44b76574a54104ed363a..ac7c46f7d9ab0d7aa021cf1568868d4113dc1100 100644 (file)
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -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);
 };