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
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@ -22,11 +22,16 @@
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#define MAX_NAME_LEN 128
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static inline u32 str_hash(const char *str)
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{
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return jhash(str, strlen(str), 0);
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}
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struct section *find_section_by_name(struct elf *elf, const char *name)
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{
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struct section *sec;
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list_for_each_entry(sec, &elf->sections, list)
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hash_for_each_possible(elf->section_name_hash, sec, name_hash, str_hash(name))
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if (!strcmp(sec->name, name))
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return sec;
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@ -202,6 +207,7 @@ static int read_sections(struct elf *elf)
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list_add_tail(&sec->list, &elf->sections);
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hash_add(elf->section_hash, &sec->hash, sec->idx);
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hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
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}
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if (stats)
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@ -441,6 +447,7 @@ struct elf *elf_read(const char *name, int flags)
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hash_init(elf->symbol_hash);
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hash_init(elf->section_hash);
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hash_init(elf->section_name_hash);
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INIT_LIST_HEAD(&elf->sections);
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elf->fd = open(name, flags);
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@ -581,6 +588,7 @@ struct section *elf_create_section(struct elf *elf, const char *name,
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list_add_tail(&sec->list, &elf->sections);
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hash_add(elf->section_hash, &sec->hash, sec->idx);
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hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
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return sec;
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}
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@ -10,6 +10,7 @@
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#include <gelf.h>
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#include <linux/list.h>
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#include <linux/hashtable.h>
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#include <linux/jhash.h>
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#ifdef LIBELF_USE_DEPRECATED
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# define elf_getshdrnum elf_getshnum
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@ -26,6 +27,7 @@
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struct section {
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struct list_head list;
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struct hlist_node hash;
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struct hlist_node name_hash;
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GElf_Shdr sh;
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struct list_head symbol_list;
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struct list_head rela_list;
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@ -73,6 +75,7 @@ struct elf {
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struct list_head sections;
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DECLARE_HASHTABLE(symbol_hash, 20);
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DECLARE_HASHTABLE(section_hash, 16);
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DECLARE_HASHTABLE(section_name_hash, 16);
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};
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