linux-kernel - [PATCH v2.1 01-A/14] objtool: Remove check preventing branches within alternative

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Message-ID: <20200429101945.GJ13592@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Apr 2020 12:19:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, alexandre.chartre@...cle.com
Cc:     linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de, x86@...nel.org, mbenes@...e.cz
Subject: [PATCH v2.1 01-A/14] objtool: Remove check preventing branches
 within alternative

Subject: objtool: Remove check preventing branches within alternative
From: Julien Thierry <jthierry@...hat.com>
Date: Fri, 27 Mar 2020 15:28:42 +0000

From: Julien Thierry <jthierry@...hat.com>

While jumping from outside an alternative region to the middle of an
alternative region is very likely wrong, jumping from an alternative
region into the same region is valid. It is a common pattern on arm64.

The first pattern is unlikely to happen in practice and checking only
for this adds a lot of complexity.

Just remove the current check.

Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Julien Thierry <jthierry@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200327152847.15294-6-jthierry@redhat.com
---
 tools/objtool/check.c |    6 ------
 1 file changed, 6 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2180,12 +2180,6 @@ static int validate_branch(struct objtoo
 
 	sec = insn->sec;
 
-	if (insn->alt_group && list_empty(&insn->alts)) {
-		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
-			  sec, insn->offset);
-		return 1;
-	}
-
 	while (1) {
 		next_insn = next_insn_same_sec(file, insn);