linux-kernel - [PATCH v2 11/14] objtool: Remove too strict constraint in jump table search

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Date:   Thu, 22 Jun 2023 12:54:33 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        Naveen N Rao <naveen@...nel.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 11/14] objtool: Remove too strict constraint in jump table search

In code there is often a pattern like:

	load jump table address
	do some test
	conditional jump to label1:
	do something
	unconditional jump to label2:
label1:
	do something else
	read jump table
	dynamic jump
label2:
	do other job here ....

find_jump_table() contains a constraint that stops the backsearch
of the table address loading when a jump is found in-between.

Remove that constraint.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 tools/objtool/check.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b810be087d7c..1911de0e1008 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2130,13 +2130,6 @@ static struct reloc *find_jump_table(struct objtool_file *file,
 		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
 			break;
 
-		/* allow small jumps within the range */
-		if (insn->type == INSN_JUMP_UNCONDITIONAL &&
-		    insn->jump_dest &&
-		    (insn->jump_dest->offset <= insn->offset ||
-		     insn->jump_dest->offset > orig_insn->offset))
-		    break;
-
 		table_reloc = arch_find_switch_table(file, insn, is_rel);
 		if (!table_reloc)
 			continue;
-- 
2.40.1