LoongArch/ftrace: Add HAVE_FUNCTION_GRAPH_RET_ADDR_PTR support

ftrace_graph_ret_addr() can be called by stack unwinding code to convert
a found stack return address ('ret') to its original value, in case the
function graph tracer has modified it to be 'return_to_handler'. If the
hasn't been modified, the unchanged value of 'ret' is returned.
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/ftrace.h

@@ -6,6 +6,8 @@
 #ifndef _ASM_LOONGARCH_FTRACE_H
 #define _ASM_LOONGARCH_FTRACE_H
 
+#define GRAPH_FAKE_OFFSET (sizeof(struct pt_regs) - offsetof(struct pt_regs, regs[1]))
+
 #ifdef CONFIG_FUNCTION_TRACER
 
 #define MCOUNT_INSN_SIZE 4		/* sizeof mcount call */
@@ -24,6 +26,7 @@ struct dyn_ftrace;
 struct dyn_arch_ftrace { };
 
 #define ARCH_SUPPORTS_FTRACE_OPS 1
+#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 
 #define ftrace_init_nop ftrace_init_nop
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);

arch/loongarch/include/asm/unwind.h

@@ -21,6 +21,7 @@ struct unwind_state {
 	struct stack_info stack_info;
 	struct task_struct *task;
 	bool first, error, is_ftrace;
+	int graph_idx;
 	unsigned long sp, pc, ra;
 };
 

arch/loongarch/kernel/ftrace_dyn.c

@@ -135,7 +135,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent)
 
 	old = *parent;
 
-	if (!function_graph_enter(old, self_addr, 0, NULL))
+	if (!function_graph_enter(old, self_addr, 0, parent))
 		*parent = return_hooker;
 }
 

arch/loongarch/kernel/unwind_guess.c

@@ -3,6 +3,7 @@
  * Copyright (C) 2022 Loongson Technology Corporation Limited
  */
 #include <linux/kernel.h>
+#include <linux/ftrace.h>
 
 #include <asm/unwind.h>
 
@@ -53,7 +54,8 @@ bool unwind_next_frame(struct unwind_state *state)
 		     state->sp < info->end;
 		     state->sp += sizeof(unsigned long)) {
 			addr = *(unsigned long *)(state->sp);
-
+			state->pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+					addr, (unsigned long *)(state->sp - GRAPH_FAKE_OFFSET));
 			if (__kernel_text_address(addr))
 				return true;
 		}

arch/loongarch/kernel/unwind_prologue.c

@@ -2,6 +2,7 @@
 /*
  * Copyright (C) 2022 Loongson Technology Corporation Limited
  */
+#include <linux/ftrace.h>
 #include <linux/kallsyms.h>
 
 #include <asm/inst.h>
@@ -42,6 +43,8 @@ static bool unwind_by_guess(struct unwind_state *state)
 	     state->sp < info->end;
 	     state->sp += sizeof(unsigned long)) {
 		addr = *(unsigned long *)(state->sp);
+		state->pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+				addr, (unsigned long *)(state->sp - GRAPH_FAKE_OFFSET));
 		if (__kernel_text_address(addr))
 			return true;
 	}
@@ -174,8 +177,11 @@ bool unwind_next_frame(struct unwind_state *state)
 			break;
 
 		case UNWINDER_PROLOGUE:
-			if (unwind_by_prologue(state))
+			if (unwind_by_prologue(state)) {
+				state->pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+						state->pc, (unsigned long *)(state->sp - GRAPH_FAKE_OFFSET));
 				return true;
+			}
 
 			if (info->type == STACK_TYPE_IRQ &&
 				info->end == state->sp) {
@@ -185,10 +191,11 @@ bool unwind_next_frame(struct unwind_state *state)
 				if (user_mode(regs) || !__kernel_text_address(pc))
 					return false;
 
-				state->pc = pc;
-				state->sp = regs->regs[3];
-				state->ra = regs->regs[1];
 				state->first = true;
+				state->ra = regs->regs[1];
+				state->sp = regs->regs[3];
+				state->pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+						pc, (unsigned long *)(state->sp - GRAPH_FAKE_OFFSET));
 				get_stack_info(state->sp, state->task, info);
 
 				return true;