LoongArch: Add USER_STACKTRACE support

To get the best stacktrace output, you can compile your userspace
programs with frame pointers (at least glibc + the app you are tracing).

1, export "CC = gcc -fno-omit-frame-pointer";
2, compile your programs with "CC";
3, use uprobe to get stacktrace output.

...
     echo 'p:malloc /usr/lib64/libc.so.6:0x0a4704 size=%r4:u64' > uprobe_events
     echo 'p:free /usr/lib64/libc.so.6:0x0a4d50 ptr=%r4:x64' >> uprobe_events
     echo 'comm == "demo"' > ./events/uprobes/malloc/filter
     echo 'comm == "demo"' > ./events/uprobes/free/filter
     echo 1 > ./options/userstacktrace
     echo 1 > ./options/sym-userobj
...
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -119,6 +119,7 @@ config LOONGARCH
 	select SWIOTLB
 	select TRACE_IRQFLAGS_SUPPORT
 	select USE_PERCPU_NUMA_NODE_ID
+	select USER_STACKTRACE_SUPPORT
 	select ZONE_DMA32
 
 config 32BIT

arch/loongarch/include/asm/stacktrace.h

@@ -21,6 +21,11 @@ struct stack_info {
 	unsigned long begin, end, next_sp;
 };
 
+struct stack_frame {
+	unsigned long	fp;
+	unsigned long	ra;
+};
+
 bool in_irq_stack(unsigned long stack, struct stack_info *info);
 bool in_task_stack(unsigned long stack, struct task_struct *task, struct stack_info *info);
 int get_stack_info(unsigned long stack, struct task_struct *task, struct stack_info *info);

arch/loongarch/kernel/stacktrace.c

@@ -6,6 +6,7 @@
  */
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
+#include <linux/uaccess.h>
 
 #include <asm/stacktrace.h>
 #include <asm/unwind.h>
@@ -35,3 +36,43 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 			break;
 	}
 }
+
+static int
+copy_stack_frame(unsigned long fp, struct stack_frame *frame)
+{
+	int ret = 1;
+	unsigned long err;
+	unsigned long __user *user_frame_tail;
+
+	user_frame_tail = (unsigned long *)(fp - sizeof(struct stack_frame));
+	if (!access_ok(user_frame_tail, sizeof(*frame)))
+		return 0;
+
+	pagefault_disable();
+	err = (__copy_from_user_inatomic(frame, user_frame_tail, sizeof(*frame)));
+	if (err || (unsigned long)user_frame_tail >= frame->fp)
+		ret = 0;
+	pagefault_enable();
+
+	return ret;
+}
+
+void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
+			  const struct pt_regs *regs)
+{
+	unsigned long fp = regs->regs[22];
+
+	while (fp && !((unsigned long)fp & 0xf)) {
+		struct stack_frame frame;
+
+		frame.fp = 0;
+		frame.ra = 0;
+		if (!copy_stack_frame(fp, &frame))
+			break;
+		if (!frame.ra)
+			break;
+		if (!consume_entry(cookie, frame.ra))
+			break;
+		fp = frame.fp;
+	}
+}