objtool: UNWIND_HINT_RET_OFFSET should not check registers

UNWIND_HINT_RET_OFFSET will adjust a modified stack. However if a
callee-saved register was pushed on the stack then the stack frame
will still appear modified. So stop checking registers when
UNWIND_HINT_RET_OFFSET is used.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200407073142.20659-3-alexandre.chartre@oracle.com

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8af8de2..068897d 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1507,6 +1507,14 @@ static bool has_modified_stack_frame(struct instruction *insn, struct insn_state
        if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
                return true;
 
+       /*
+        * If there is a ret offset hint then don't check registers
+        * because a callee-saved register might have been pushed on
+        * the stack.
+        */
+       if (ret_offset)
+               return false;
+
        for (i = 0; i < CFI_NUM_REGS; i++) {
                if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
                    cfi->regs[i].offset != initial_func_cfi.regs[i].offset)