LoongArch: Add kprobes on ftrace support

Add kprobe_ftrace_handler() and arch_prepare_kprobe_ftrace() to support
kprobes on ftrace, the code is similar with x86 and riscv.

Here is a simple example:

  # echo 'p:myprobe kernel_clone' > /sys/kernel/debug/tracing/kprobe_events
  # echo 'r:myretprobe kernel_clone $retval' >> /sys/kernel/debug/tracing/kprobe_events
  # echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
  # echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
  # echo 1 > /sys/kernel/debug/tracing/tracing_on
  # cat /sys/kernel/debug/tracing/trace
  # tracer: nop
  #
  # entries-in-buffer/entries-written: 2/2   #P:4
  #
  #                                _-----=> irqs-off/BH-disabled
  #                               / _----=> need-resched
  #                              | / _---=> hardirq/softirq
  #                              || / _--=> preempt-depth
  #                              ||| / _-=> migrate-disable
  #                              |||| /     delay
  #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
  #              | |         |   |||||     |         |
              bash-488     [002] .....  2041.190681: myprobe: (kernel_clone+0x0/0x40c)
              bash-488     [002] .....  2041.190788: myretprobe: (__do_sys_clone+0x84/0xb8 <- kernel_clone) arg1=0x200

Tested-by: Jeff Xie <xiehuan09@gmail.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -107,6 +107,7 @@ config LOONGARCH
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK
 	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_KPROBES
+	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI

arch/loongarch/kernel/ftrace_dyn.c

@@ -6,6 +6,7 @@
  */
 
 #include <linux/ftrace.h>
+#include <linux/kprobes.h>
 #include <linux/uaccess.h>
 
 #include <asm/inst.h>
@@ -271,3 +272,66 @@ int ftrace_disable_ftrace_graph_caller(void)
 }
 #endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+#ifdef CONFIG_KPROBES_ON_FTRACE
+/* Ftrace callback handler for kprobes -- called under preepmt disabled */
+void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
+			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
+{
+	int bit;
+	struct pt_regs *regs;
+	struct kprobe *p;
+	struct kprobe_ctlblk *kcb;
+
+	bit = ftrace_test_recursion_trylock(ip, parent_ip);
+	if (bit < 0)
+		return;
+
+	p = get_kprobe((kprobe_opcode_t *)ip);
+	if (unlikely(!p) || kprobe_disabled(p))
+		goto out;
+
+	regs = ftrace_get_regs(fregs);
+	if (!regs)
+		goto out;
+
+	kcb = get_kprobe_ctlblk();
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(p);
+	} else {
+		unsigned long orig_ip = instruction_pointer(regs);
+
+		instruction_pointer_set(regs, ip);
+
+		__this_cpu_write(current_kprobe, p);
+		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+		if (!p->pre_handler || !p->pre_handler(p, regs)) {
+			/*
+			 * Emulate singlestep (and also recover regs->csr_era)
+			 * as if there is a nop
+			 */
+			instruction_pointer_set(regs, (unsigned long)p->addr + MCOUNT_INSN_SIZE);
+			if (unlikely(p->post_handler)) {
+				kcb->kprobe_status = KPROBE_HIT_SSDONE;
+				p->post_handler(p, regs, 0);
+			}
+			instruction_pointer_set(regs, orig_ip);
+		}
+
+		/*
+		 * If pre_handler returns !0, it changes regs->csr_era. We have to
+		 * skip emulating post_handler.
+		 */
+		__this_cpu_write(current_kprobe, NULL);
+	}
+out:
+	ftrace_test_recursion_unlock(bit);
+}
+NOKPROBE_SYMBOL(kprobe_ftrace_handler);
+
+int arch_prepare_kprobe_ftrace(struct kprobe *p)
+{
+	p->ainsn.insn = NULL;
+	return 0;
+}
+#endif /* CONFIG_KPROBES_ON_FTRACE */