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Date:   Fri, 15 Oct 2021 21:51:29 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Ananth N Mavinakayanahalli <ananth@...ux.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        mhiramat@...nel.org, Sven Schnelle <svens@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 05/10] arm64: kprobes: Make a frame pointer on __kretprobe_trampoline

Make a frame pointer (make the x29 register points the
address of pt_regs->regs[29]) on __kretprobe_trampoline.

This frame pointer will be used by the stacktracer when it is
called from the kretprobe handlers. In this case, the stack
tracer will unwind stack to trampoline_probe_handler() and
find the next frame pointer in the stack frame of the
__kretprobe_trampoline().

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Acked-by: Will Deacon <will@...nel.org>
---
 arch/arm64/kernel/probes/kprobes_trampoline.S |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kernel/probes/kprobes_trampoline.S b/arch/arm64/kernel/probes/kprobes_trampoline.S
index 520ee8711db1..9a6499bed58b 100644
--- a/arch/arm64/kernel/probes/kprobes_trampoline.S
+++ b/arch/arm64/kernel/probes/kprobes_trampoline.S
@@ -66,6 +66,9 @@ SYM_CODE_START(__kretprobe_trampoline)
 
 	save_all_base_regs
 
+	/* Setup a frame pointer. */
+	add x29, sp, #S_FP
+
 	mov x0, sp
 	bl trampoline_probe_handler
 	/*
@@ -74,6 +77,7 @@ SYM_CODE_START(__kretprobe_trampoline)
 	 */
 	mov lr, x0
 
+	/* The frame pointer (x29) is restored with other registers. */
 	restore_all_base_regs
 
 	add sp, sp, #PT_REGS_SIZE

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