linux-kernel - [tip:x86/asm] objtool: Skip unreachable warnings for 'alt' instructions

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Message-ID: <tip-0e2bb2bc14b3df754b0a86e87cd8923df0701a1b@git.kernel.org>
Date:   Fri, 28 Jul 2017 00:37:31 -0700
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        hpa@...or.com, tglx@...utronix.de, mingo@...nel.org,
        torvalds@...ux-foundation.org, peterz@...radead.org
Subject: [tip:x86/asm] objtool: Skip unreachable warnings for 'alt'
 instructions

Commit-ID:  0e2bb2bc14b3df754b0a86e87cd8923df0701a1b
Gitweb:     http://git.kernel.org/tip/0e2bb2bc14b3df754b0a86e87cd8923df0701a1b
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Thu, 27 Jul 2017 15:56:54 -0500
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 28 Jul 2017 08:33:32 +0200

objtool: Skip unreachable warnings for 'alt' instructions

When a whitelisted function uses one of the ALTERNATIVE macros, it
produces false positive warnings like:

  arch/x86/kvm/vmx.o: warning: objtool: .altinstr_replacement+0x0: unreachable instruction
  arch/x86/kvm/svm.o: warning: objtool: .altinstr_replacement+0x6e: unreachable instruction

There's no easy way to whitelist alternative instructions, so instead
just skip any 'unreachable' warnings associated with them.

Reported-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/a5d0a8c60155f03b36a31fac871e12cf75f35fd0.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 tools/objtool/check.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index d07bf4a..4f0c4ae 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1746,8 +1746,13 @@ static bool ignore_unreachable_insn(struct instruction *insn)
 	/*
 	 * Ignore any unused exceptions.  This can happen when a whitelisted
 	 * function has an exception table entry.
+	 *
+	 * Also ignore alternative replacement instructions.  This can happen
+	 * when a whitelisted function uses one of the ALTERNATIVE macros.
 	 */
-	if (!strcmp(insn->sec->name, ".fixup"))
+	if (!strcmp(insn->sec->name, ".fixup") ||
+	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
+	    !strcmp(insn->sec->name, ".altinstr_aux"))
 		return true;
 
 	/*