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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@redhat.com>
AuthorDate: Thu, 27 Jul 2017 15:56:54 -0500
Committer: Ingo Molnar <mingo@kernel.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@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a5d0a8c60155f03b36a31fac871e12cf75f35fd0.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.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;

/*
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