[PATCH 4/8] arm64: kprobes: Make a frame pointer on __kretprobe_trampoline

Masami Hiramatsu
2021-10-08T12:28:55Z

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@kernel.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