linux-kernel - [PATCH 2/3] objtool: optimize insn

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Message-Id: <20200421180724.245410-3-samitolvanen@google.com>
Date:   Tue, 21 Apr 2020 11:07:23 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 2/3] objtool: optimize insn_hash for split sections

When running objtool on vmlinux.o compiled with -ffunction-sections,
we end up with a ton of collisions in the insn_hash table as each
function is in its own section. This results in a runtime of minutes
instead of seconds. Use both section index and offset as the key to
avoid this, similarly to rela_hash.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 tools/objtool/check.c | 5 +++--
 tools/objtool/check.h | 5 +++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4b170fd08a28..4770fb07b365 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -34,7 +34,8 @@ struct instruction *find_insn(struct objtool_file *file,
 {
 	struct instruction *insn;
 
-	hash_for_each_possible(file->insn_hash, insn, hash, offset)
+	hash_for_each_possible(file->insn_hash, insn, hash,
+			       sec_offset_hash(sec, offset))
 		if (insn->sec == sec && insn->offset == offset)
 			return insn;
 
@@ -273,7 +274,7 @@ static int decode_instructions(struct objtool_file *file)
 			if (ret)
 				goto err;
 
-			hash_add(file->insn_hash, &insn->hash, insn->offset);
+			hash_add(file->insn_hash, &insn->hash, insn_hash(insn));
 			list_add_tail(&insn->list, &file->insn_list);
 			nr_insns++;
 		}
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index f0ce8ffe7135..bc78eca7982e 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -56,6 +56,11 @@ struct objtool_file {
 
 int check(const char *objname, bool orc);
 
+static inline u32 insn_hash(struct instruction *insn)
+{
+	return sec_offset_hash(insn->sec, insn->offset);
+}
+
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);
 
-- 
2.26.1.301.g55bc3eb7cb9-goog