LoongArch: Use correct sp value to get graph addr in stack unwinders

The stack frame when function_graph enable like follows,

---------  <- function sp_on_entry
    |
    |
    |
 FAKE_RA   <- sp_on_entry - sizeof(pt_regs) + PT_R1
    |
---------  <- sp_on_entry - sizeof(pt_regs)

So if we want to get the &FAKE_RA we should get sp_on_entry first. In
the unwinder_prologue case, we can get the sp_on_entry as state->sp,
because we try to calculate each CFA and the ra saved address. But in
the unwinder_guess case, we cannot get it because we do not try to
calculate the CFA. Although LoongArch have not fixed frame, the $ra is
saved at CFA - 8 in most cases, we can try guess, too. As we store the
pc in state, we not need to dereference state->sp, too.
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/ftrace.h

@@ -10,8 +10,6 @@
 #define FTRACE_REGS_PLT_IDX	1
 #define NR_FTRACE_PLTS		2
 
-#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 */

arch/loongarch/include/asm/unwind.h

@@ -8,7 +8,9 @@
 #define _ASM_UNWIND_H
 
 #include <linux/sched.h>
+#include <linux/ftrace.h>
 
+#include <asm/ptrace.h>
 #include <asm/stacktrace.h>
 
 enum unwinder_type {
@@ -40,4 +42,12 @@ static inline bool unwind_error(struct unwind_state *state)
 	return state->error;
 }
 
+#define GRAPH_FAKE_OFFSET (sizeof(struct pt_regs) - offsetof(struct pt_regs, regs[1]))
+
+static inline unsigned long unwind_graph_addr(struct unwind_state *state,
+					unsigned long pc, unsigned long cfa)
+{
+	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
+				     pc, (unsigned long *)(cfa - GRAPH_FAKE_OFFSET));
+}
 #endif /* _ASM_UNWIND_H */

arch/loongarch/kernel/unwind_guess.c

@@ -11,10 +11,8 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
 {
 	if (unwind_done(state))
 		return 0;
-	else if (state->first)
-		return state->pc;
 
-	return *(unsigned long *)(state->sp);
+	return state->pc;
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
@@ -36,7 +34,7 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
 
 	state->task = task;
 	state->first = true;
-
+	state->pc = unwind_graph_addr(state, state->pc, state->sp);
 	get_stack_info(state->sp, state->task, &state->stack_info);
 
 	if (!unwind_done(state) && !__kernel_text_address(state->pc))
@@ -60,9 +58,8 @@ 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))
+			state->pc = unwind_graph_addr(state, addr, state->sp + 8);
+			if (__kernel_text_address(state->pc))
 				return true;
 		}
 

arch/loongarch/kernel/unwind_prologue.c

@@ -21,16 +21,10 @@ static inline void unwind_state_fixup(struct unwind_state *state)
 
 unsigned long unwind_get_return_address(struct unwind_state *state)
 {
-
 	if (unwind_done(state))
 		return 0;
-	else if (state->type)
-		return state->pc;
-	else if (state->first)
-		return state->pc;
-
-	return *(unsigned long *)(state->sp);
 
+	return state->pc;
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
@@ -43,9 +37,8 @@ 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))
+		state->pc = unwind_graph_addr(state, addr, state->sp + 8);
+		if (__kernel_text_address(state->pc))
 			return true;
 	}
 
@@ -166,7 +159,7 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
 
 	state->task = task;
 	state->first = true;
-
+	state->pc = unwind_graph_addr(state, state->pc, state->sp);
 	get_stack_info(state->sp, state->task, &state->stack_info);
 
 	if (!unwind_done(state) && !__kernel_text_address(state->pc))
@@ -193,8 +186,7 @@ bool unwind_next_frame(struct unwind_state *state)
 
 		case UNWINDER_PROLOGUE:
 			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));
+				state->pc = unwind_graph_addr(state, state->pc, state->sp);
 				return true;
 			}
 
@@ -209,8 +201,7 @@ bool unwind_next_frame(struct unwind_state *state)
 				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));
+				state->pc = pc;
 				get_stack_info(state->sp, state->task, info);
 
 				return true;