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@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/arch/arm64/kernel/probes/kprobes_trampoline.S b/arch/arm64/kernel/probes/kprobes_trampoline.S
index 520ee87..9a6499b 100644 (file)
--- 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