[PATCH v4 1/4] objtool: Fix INSN_CONTEXT_SWITCH handling in validate_unret()

[Josh Poimboeuf]

The !CONFIG_IA32_EMULATION version of xen_entry_SYSCALL_compat() ends
with a SYSCALL instruction which is classified by objtool as
INSN_CONTEXT_SWITCH.

Unlike validate_branch(), validate_unret() doesn't consider
INSN_CONTEXT_SWITCH in a non-function to be a dead end, so it keeps
going past the end of xen_entry_SYSCALL_compat(), resulting in the
following warning:

  vmlinux.o: warning: objtool: xen_reschedule_interrupt+0x2a: RET before UNTRAIN

Fix that by adding INSN_CONTEXT_SWITCH handling to validate_unret() to
match what validate_branch() is already doing.

Fixes: a09a6e2399ba ("objtool: Add entry UNRET validation")
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4a1f6c3169b3..c81b070ca495 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3886,6 +3886,11 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
 			WARN_INSN(insn, "RET before UNTRAIN");
 			return 1;
 
+		case INSN_CONTEXT_SWITCH:
+			if (insn_func(insn))
+				break;
+			return 0;
+
 		case INSN_NOP:
 			if (insn->retpoline_safe)
 				return 0;
-- 
2.49.0