[RFC][PATCH 05/16] objtool: Optimize find_symbol_by_index()

Peter Zijlstra
2020-03-12T13:52:04Z

The symbol index is object wide, not per section, so it makes no sense
to have the symbol_hash be part of the section object. By moving it to
the elf object we avoid the linear sections iteration.

This reduces the runtime of objtool on vmlinux.o from over 3 hours (I
gave up) to a few minutes. The defconfig vmlinux.o has around 20k
sections.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/elf.c | 14 ++++++--------
tools/objtool/elf.h | 3 +--
2 files changed, 7 insertions(+), 10 deletions(-)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -46,13 +46,11 @@ static struct section *find_section_by_i

static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
{
- struct section *sec;
struct symbol *sym;

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

return NULL;
}
@@ -156,7 +154,6 @@ static int read_sections(struct elf *elf
INIT_LIST_HEAD(&sec->symbol_list);
INIT_LIST_HEAD(&sec->rela_list);
hash_init(sec->rela_hash);
- hash_init(sec->symbol_hash);

list_add_tail(&sec->list, &elf->sections);

@@ -289,7 +286,8 @@ static int read_symbols(struct elf *elf)
}
sym->alias = alias;
list_add(&sym->list, entry);
- hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
+
+ hash_add(elf->symbol_hash, &sym->hash, sym->idx);
}

/* Create parent/child links for any cold subfunctions */
@@ -415,6 +413,7 @@ struct elf *elf_read(const char *name, i
}
memset(elf, 0, sizeof(*elf));

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

elf->fd = open(name, flags);
@@ -476,7 +475,6 @@ struct section *elf_create_section(struc
INIT_LIST_HEAD(&sec->symbol_list);
INIT_LIST_HEAD(&sec->rela_list);
hash_init(sec->rela_hash);
- hash_init(sec->symbol_hash);

list_add_tail(&sec->list, &elf->sections);

--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -27,7 +27,6 @@ struct section {
struct list_head list;
GElf_Shdr sh;
struct list_head symbol_list;
- DECLARE_HASHTABLE(symbol_hash, 8);
struct list_head rela_list;
DECLARE_HASHTABLE(rela_hash, 16);
struct section *base, *rela;
@@ -71,7 +70,7 @@ struct elf {
int fd;
char *name;
struct list_head sections;
- DECLARE_HASHTABLE(rela_hash, 16);
+ DECLARE_HASHTABLE(symbol_hash, 20);
};