s390/unwind: introduce stack unwind API

Rework the dump_trace() stack unwinder interface to support different
unwinding algorithms. The new interface looks like this:

	struct unwind_state state;
	unwind_for_each_frame(&state, task, regs, start_stack)
		do_something(state.sp, state.ip, state.reliable);

The unwind_bc.c file contains the implementation for the classic
back-chain unwinder.

One positive side effect of the new code is it now handles ftraced
functions gracefully. It prints the real name of the return function
instead of 'return_to_handler'.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 155 insertions, 0 deletions

diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
new file mode 100644
index 000000000000..cf5a630f3aa9
--- /dev/null
+++ b/arch/s390/kernel/unwind_bc.c
@@ -0,0 +1,155 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/interrupt.h>
+#include <asm/sections.h>
+#include <asm/ptrace.h>
+#include <asm/bitops.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+	if (unwind_done(state))
+		return 0;
+	return __kernel_text_address(state->ip) ? state->ip : 0;
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+static bool outside_of_stack(struct unwind_state *state, unsigned long sp)
+{
+	return (sp <= state->sp) ||
+		(sp + sizeof(struct stack_frame) > state->stack_info.end);
+}
+
+static bool update_stack_info(struct unwind_state *state, unsigned long sp)
+{
+	struct stack_info *info = &state->stack_info;
+	unsigned long *mask = &state->stack_mask;
+
+	/* New stack pointer leaves the current stack */
+	if (get_stack_info(sp, state->task, info, mask) != 0 ||
+	    !on_stack(info, sp, sizeof(struct stack_frame)))
+		/* 'sp' does not point to a valid stack */
+		return false;
+	return true;
+}
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+	struct stack_info *info = &state->stack_info;
+	struct stack_frame *sf;
+	struct pt_regs *regs;
+	unsigned long sp, ip;
+	bool reliable;
+
+	regs = state->regs;
+	if (unlikely(regs)) {
+		sp = READ_ONCE_TASK_STACK(state->task, regs->gprs[15]);
+		if (unlikely(outside_of_stack(state, sp))) {
+			if (!update_stack_info(state, sp))
+				goto out_err;
+		}
+		sf = (struct stack_frame *) sp;
+		ip = READ_ONCE_TASK_STACK(state->task, sf->gprs[8]);
+		reliable = false;
+		regs = NULL;
+	} else {
+		sf = (struct stack_frame *) state->sp;
+		sp = READ_ONCE_TASK_STACK(state->task, sf->back_chain);
+		if (likely(sp)) {
+			/* Non-zero back-chain points to the previous frame */
+			if (unlikely(outside_of_stack(state, sp))) {
+				if (!update_stack_info(state, sp))
+					goto out_err;
+			}
+			sf = (struct stack_frame *) sp;
+			ip = READ_ONCE_TASK_STACK(state->task, sf->gprs[8]);
+			reliable = true;
+		} else {
+			/* No back-chain, look for a pt_regs structure */
+			sp = state->sp + STACK_FRAME_OVERHEAD;
+			if (!on_stack(info, sp, sizeof(struct pt_regs)))
+				goto out_stop;
+			regs = (struct pt_regs *) sp;
+			if (user_mode(regs))
+				goto out_stop;
+			ip = READ_ONCE_TASK_STACK(state->task, regs->psw.addr);
+			reliable = true;
+		}
+	}
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	/* Decode any ftrace redirection */
+	if (ip == (unsigned long) return_to_handler)
+		ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+					   ip, NULL);
+#endif
+
+	/* Update unwind state */
+	state->sp = sp;
+	state->ip = ip;
+	state->regs = regs;
+	state->reliable = reliable;
+	return true;
+
+out_err:
+	state->error = true;
+out_stop:
+	state->stack_info.type = STACK_TYPE_UNKNOWN;
+	return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
+
+void __unwind_start(struct unwind_state *state, struct task_struct *task,
+		    struct pt_regs *regs, unsigned long sp)
+{
+	struct stack_info *info = &state->stack_info;
+	unsigned long *mask = &state->stack_mask;
+	struct stack_frame *sf;
+	unsigned long ip;
+	bool reliable;
+
+	memset(state, 0, sizeof(*state));
+	state->task = task;
+	state->regs = regs;
+
+	/* Don't even attempt to start from user mode regs: */
+	if (regs && user_mode(regs)) {
+		info->type = STACK_TYPE_UNKNOWN;
+		return;
+	}
+
+	/* Get current stack pointer and initialize stack info */
+	if (get_stack_info(sp, task, info, mask) != 0 ||
+	    !on_stack(info, sp, sizeof(struct stack_frame))) {
+		/* Something is wrong with the stack pointer */
+		info->type = STACK_TYPE_UNKNOWN;
+		state->error = true;
+		return;
+	}
+
+	/* Get the instruction pointer from pt_regs or the stack frame */
+	if (regs) {
+		ip = READ_ONCE_TASK_STACK(state->task, regs->psw.addr);
+		reliable = true;
+	} else {
+		sf = (struct stack_frame *) sp;
+		ip = READ_ONCE_TASK_STACK(state->task, sf->gprs[8]);
+		reliable = false;
+	}
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	/* Decode any ftrace redirection */
+	if (ip == (unsigned long) return_to_handler)
+		ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+					   ip, NULL);
+#endif
+
+	/* Update unwind state */
+	state->sp = sp;
+	state->ip = ip;
+	state->reliable = reliable;
+}
+EXPORT_SYMBOL_GPL(__unwind_start);