[tip: core/objtool] objtool: Optimize read_sections()

From: tip-bot2 for Peter Zijlstra
Date: Thu Mar 26 2020 - 06:09:12 EST

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The following commit has been merged into the core/objtool branch of tip:

Commit-ID: 8b5fa6bc326bf02f293b5a39a8f5b3de816265d3
Gitweb: https://git.kernel.org/tip/8b5fa6bc326bf02f293b5a39a8f5b3de816265d3
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 12 Mar 2020 11:23:36 +01:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 25 Mar 2020 18:28:30 +01:00

objtool: Optimize read_sections()

Perf showed that __hash_init() is a significant portion of
read_sections(), so instead of doing a per section rela_hash, use an
elf-wide rela_hash.

Statistics show us there are about 1.1 million relas, so size it
accordingly.

This reduces the objtool on vmlinux.o runtime to a third, from 15 to 5
seconds.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200324160924.739153726@xxxxxxxxxxxxx
---
tools/objtool/check.c | 18 +++++++++---------
tools/objtool/elf.c | 24 ++++++++++++++----------
tools/objtool/elf.h | 21 +++++++++++++++++----
tools/objtool/orc_gen.c | 9 +++++----
tools/objtool/special.c | 4 ++--
5 files changed, 47 insertions(+), 29 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6df1bae..54a6043 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -569,8 +569,8 @@ static int add_jump_destinations(struct objtool_file *file)
if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
continue;

- rela = find_rela_by_dest_range(insn->sec, insn->offset,
- insn->len);
+ rela = find_rela_by_dest_range(file->elf, insn->sec,
+ insn->offset, insn->len);
if (!rela) {
dest_sec = insn->sec;
dest_off = insn->offset + insn->len + insn->immediate;
@@ -666,8 +666,8 @@ static int add_call_destinations(struct objtool_file *file)
if (insn->type != INSN_CALL)
continue;

- rela = find_rela_by_dest_range(insn->sec, insn->offset,
- insn->len);
+ rela = find_rela_by_dest_range(file->elf, insn->sec,
+ insn->offset, insn->len);
if (!rela) {
dest_off = insn->offset + insn->len + insn->immediate;
insn->call_dest = find_func_by_offset(insn->sec, dest_off);
@@ -796,7 +796,7 @@ static int handle_group_alt(struct objtool_file *file,
*/
if ((insn->offset != special_alt->new_off ||
(insn->type != INSN_CALL && !is_static_jump(insn))) &&
- find_rela_by_dest_range(insn->sec, insn->offset, insn->len)) {
+ find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {

WARN_FUNC("unsupported relocation in alternatives section",
insn->sec, insn->offset);
@@ -1066,8 +1066,8 @@ static struct rela *find_jump_table(struct objtool_file *file,
break;

/* look for a relocation which references .rodata */
- text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
- insn->len);
+ text_rela = find_rela_by_dest_range(file->elf, insn->sec,
+ insn->offset, insn->len);
if (!text_rela || text_rela->sym->type != STT_SECTION ||
!text_rela->sym->sec->rodata)
continue;
@@ -1096,7 +1096,7 @@ static struct rela *find_jump_table(struct objtool_file *file,
* should reference text in the same function as the original
* instruction.
*/
- table_rela = find_rela_by_dest(table_sec, table_offset);
+ table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
if (!table_rela)
continue;
dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
@@ -1232,7 +1232,7 @@ static int read_unwind_hints(struct objtool_file *file)
for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
hint = (struct unwind_hint *)sec->data->d_buf + i;

- rela = find_rela_by_dest(sec, i * sizeof(*hint));
+ rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
if (!rela) {
WARN("can't find rela for unwind_hints[%d]", i);
return -1;
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 43abae7..8a0a1bc 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -212,8 +212,8 @@ struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
return NULL;
}

-struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
- unsigned int len)
+struct rela *find_rela_by_dest_range(struct elf *elf, struct section *sec,
+ unsigned long offset, unsigned int len)
{
struct rela *rela;
unsigned long o;
@@ -221,17 +221,22 @@ struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
if (!sec->rela)
return NULL;

- for (o = offset; o < offset + len; o++)
- hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
- if (rela->offset == o)
+ sec = sec->rela;
+
+ for (o = offset; o < offset + len; o++) {
+ hash_for_each_possible(elf->rela_hash, rela, hash,
+ sec_offset_hash(sec, o)) {
+ if (rela->sec == sec && rela->offset == o)
return rela;
+ }
+ }

return NULL;
}

-struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
+struct rela *find_rela_by_dest(struct elf *elf, struct section *sec, unsigned long offset)
{
- return find_rela_by_dest_range(sec, offset, 1);
+ return find_rela_by_dest_range(elf, sec, offset, 1);
}

static int read_sections(struct elf *elf)
@@ -261,7 +266,6 @@ static int read_sections(struct elf *elf)

INIT_LIST_HEAD(&sec->symbol_list);
INIT_LIST_HEAD(&sec->rela_list);
- hash_init(sec->rela_hash);

s = elf_getscn(elf->elf, i);
if (!s) {
@@ -493,7 +497,7 @@ static int read_relas(struct elf *elf)
}

list_add_tail(&rela->list, &sec->rela_list);
- hash_add(sec->rela_hash, &rela->hash, rela->offset);
+ hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));
nr_rela++;
}
max_rela = max(max_rela, nr_rela);
@@ -526,6 +530,7 @@ struct elf *elf_read(const char *name, int flags)
hash_init(elf->symbol_name_hash);
hash_init(elf->section_hash);
hash_init(elf->section_name_hash);
+ hash_init(elf->rela_hash);
INIT_LIST_HEAD(&elf->sections);

elf->fd = open(name, flags);
@@ -586,7 +591,6 @@ 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);

s = elf_newscn(elf->elf);
if (!s) {
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 3088d92..dfd2431 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -33,7 +33,6 @@ struct section {
struct rb_root symbol_tree;
struct list_head symbol_list;
struct list_head rela_list;
- DECLARE_HASHTABLE(rela_hash, 16);
struct section *base, *rela;
struct symbol *sym;
Elf_Data *data;
@@ -81,8 +80,22 @@ struct elf {
DECLARE_HASHTABLE(symbol_name_hash, 20);
DECLARE_HASHTABLE(section_hash, 16);
DECLARE_HASHTABLE(section_name_hash, 16);
+ DECLARE_HASHTABLE(rela_hash, 20);
};

+static inline u32 sec_offset_hash(struct section *sec, unsigned long offset)
+{
+ u32 ol = offset, oh = offset >> 32, idx = sec->idx;
+
+ __jhash_mix(ol, oh, idx);
+
+ return ol;
+}
+
+static inline u32 rela_hash(struct rela *rela)
+{
+ return sec_offset_hash(rela->sec, rela->offset);
+}

struct elf *elf_read(const char *name, int flags);
struct section *find_section_by_name(struct elf *elf, const char *name);
@@ -90,9 +103,9 @@ struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);
struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
struct symbol *find_symbol_by_name(struct elf *elf, const char *name);
struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);
-struct rela *find_rela_by_dest(struct section *sec, unsigned long offset);
-struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
- unsigned int len);
+struct rela *find_rela_by_dest(struct elf *elf, struct section *sec, unsigned long offset);
+struct rela *find_rela_by_dest_range(struct elf *elf, struct section *sec,
+ unsigned long offset, unsigned int len);
struct symbol *find_func_containing(struct section *sec, unsigned long offset);
struct section *elf_create_section(struct elf *elf, const char *name, size_t
entsize, int nr);
diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
index 27a4112..41e4a27 100644
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -81,7 +81,7 @@ int create_orc(struct objtool_file *file)
return 0;
}

-static int create_orc_entry(struct section *u_sec, struct section *ip_relasec,
+static int create_orc_entry(struct elf *elf, struct section *u_sec, struct section *ip_relasec,
unsigned int idx, struct section *insn_sec,
unsigned long insn_off, struct orc_entry *o)
{
@@ -109,9 +109,10 @@ static int create_orc_entry(struct section *u_sec, struct section *ip_relasec,
rela->addend = insn_off;
rela->type = R_X86_64_PC32;
rela->offset = idx * sizeof(int);
+ rela->sec = ip_relasec;

list_add_tail(&rela->list, &ip_relasec->rela_list);
- hash_add(ip_relasec->rela_hash, &rela->hash, rela->offset);
+ hash_add(elf->rela_hash, &rela->hash, rela_hash(rela));

return 0;
}
@@ -182,7 +183,7 @@ int create_orc_sections(struct objtool_file *file)
if (!prev_insn || memcmp(&insn->orc, &prev_insn->orc,
sizeof(struct orc_entry))) {

- if (create_orc_entry(u_sec, ip_relasec, idx,
+ if (create_orc_entry(file->elf, u_sec, ip_relasec, idx,
insn->sec, insn->offset,
&insn->orc))
return -1;
@@ -194,7 +195,7 @@ int create_orc_sections(struct objtool_file *file)

/* section terminator */
if (prev_insn) {
- if (create_orc_entry(u_sec, ip_relasec, idx,
+ if (create_orc_entry(file->elf, u_sec, ip_relasec, idx,
prev_insn->sec,
prev_insn->offset + prev_insn->len,
&empty))
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index fdbaa61..e74e018 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -118,7 +118,7 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
}
}

- orig_rela = find_rela_by_dest(sec, offset + entry->orig);
+ orig_rela = find_rela_by_dest(elf, sec, offset + entry->orig);
if (!orig_rela) {
WARN_FUNC("can't find orig rela", sec, offset + entry->orig);
return -1;
@@ -133,7 +133,7 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
alt->orig_off = orig_rela->addend;

if (!entry->group || alt->new_len) {
- new_rela = find_rela_by_dest(sec, offset + entry->new);
+ new_rela = find_rela_by_dest(elf, sec, offset + entry->new);
if (!new_rela) {
WARN_FUNC("can't find new rela",
sec, offset + entry->new);

Next message: tip-bot2 for Peter Zijlstra: "[tip: core/objtool] objtool: Optimize find_symbol_*() and read_symbols()"
Previous message: tip-bot2 for Peter Zijlstra: "[tip: core/objtool] objtool: Rename func_for_each_insn_all()"
In reply to: Miroslav Benes: "Re: [PATCH v3 14/26] objtool: Optimize read_sections()"
Next in thread: Peter Zijlstra: "[PATCH v3 25/26] objtool: Rearrange validate_section()"
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