linux-kernel - [RFC][PATCH 2/7] objtool: UNWIND_HINT_RET

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Message-Id: <20200416151024.825863887@infradead.org>
Date:   Thu, 16 Apr 2020 17:07:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, alexandre.chartre@...cle.com
Cc:     linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de, x86@...nel.org, peterz@...radead.org
Subject: [RFC][PATCH 2/7] objtool: UNWIND_HINT_RET_OFFSET should not check registers

From: Alexandre Chartre <alexandre.chartre@...cle.com>

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@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200407073142.20659-3-alexandre.chartre@oracle.com
---
 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)