[tip: objtool/core] objtool: Ignore unreachable fake jumps

[tip-bot2 for Julien Thierry]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     fb136219f0e2b417d84e67b2a3adc1f933997d04
Gitweb:        https://git.kernel.org/tip/fb136219f0e2b417d84e67b2a3adc1f933997d04
Author:        Julien Thierry <jthierry@xxxxxxxxxx>
AuthorDate:    Tue, 15 Sep 2020 08:53:17 +01:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Fri, 18 Sep 2020 12:04:00 -05:00

objtool: Ignore unreachable fake jumps

It is possible for alternative code to unconditionally jump out of the
alternative region. In such a case, if a fake jump is added at the end
of the alternative instructions, the fake jump will never be reached.
Since the fake jump is just a mean to make sure code validation does not
go beyond the set of alternatives, reaching it is not a requirement.

Signed-off-by: Julien Thierry <jthierry@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index fd2edab..cd7c669 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2648,6 +2648,9 @@ static bool ignore_unreachable_insn(struct instruction *insn)
 	    !strcmp(insn->sec->name, ".altinstr_aux"))
 		return true;
 
+	if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->offset == FAKE_JUMP_OFFSET)
+		return true;
+
 	if (!insn->func)
 		return false;