linux-kernel - [PATCH] x86/unwind/orc: Do not skip the first frame unless explicitly asked for

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Date:   Wed,  4 Mar 2020 13:32:59 +0100
From:   Miroslav Benes <mbenes@...e.cz>
To:     jpoimboe@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de
Cc:     hpa@...or.com, linux-kernel@...r.kernel.org, x86@...nel.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: [PATCH] x86/unwind/orc: Do not skip the first frame unless explicitly asked for

ORC unwinder can currently skip the first frame even if a user does not
ask for it. If both regs and first_frame parameters of unwind_start()
are set to NULL, state->sp and first_frame are later initialized to the
same value for an inactive task. Given there is "less than or equal to"
comparison used at the end of __unwind_start() for skipping stack frames,
the first frame is always skipped in this case.

Drop the equal part of the comparison and make it equivalent to the
frame pointer unwinder.

Signed-off-by: Miroslav Benes <mbenes@...e.cz>
---
 arch/x86/kernel/unwind_orc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index e9cc182aa97e..8452518cc20a 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -651,7 +651,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	/* Otherwise, skip ahead to the user-specified starting frame: */
 	while (!unwind_done(state) &&
 	       (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
-			state->sp <= (unsigned long)first_frame))
+			state->sp < (unsigned long)first_frame))
 		unwind_next_frame(state);

 	return;
-- 
2.25.1