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Subject[tip: core/objtool] objtool: Optimize find_symbol_by_index()
The following commit has been merged into the core/objtool branch of tip:

Commit-ID: 65fb11a7f6aeae678043738d06248a4e21f4e4e4
Gitweb: https://git.kernel.org/tip/65fb11a7f6aeae678043738d06248a4e21f4e4e4
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 10 Mar 2020 18:39:45 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 25 Mar 2020 18:28:28 +01:00

objtool: Optimize find_symbol_by_index()

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>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.261852348@infradead.org
---
tools/objtool/elf.c | 13 +++++--------
tools/objtool/elf.h | 3 +--
2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index cc4601c..b188b3e 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -46,13 +46,11 @@ static struct section *find_section_by_index(struct elf *elf,

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;
}
@@ -166,7 +164,6 @@ 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);

@@ -299,7 +296,7 @@ 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 */
@@ -425,6 +422,7 @@ struct elf *elf_read(const char *name, int flags)
}
memset(elf, 0, sizeof(*elf));

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

elf->fd = open(name, flags);
@@ -486,7 +484,6 @@ struct section *elf_create_section(struct elf *elf, const char *name,
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);

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index a196325..1222980 100644
--- 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);
};


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