[RFC][PATCH 2/7] objtool: UNWIND_HINT_RET_OFFSET should not check registers

From: Peter Zijlstra
Date: Thu Apr 16 2020 - 11:16:05 EST


From: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200407073142.20659-3-alexandre.chartre@xxxxxxxxxx
---
tools/objtool/check.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1513,6 +1513,14 @@ static bool has_modified_stack_frame(str
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)