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From:   Jinyang He <hejinyang@loongson.cn>
To:     Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Qing Zhang <zhangqing@loongson.cn>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>
Subject: [PATCH v3 4/5] LoongArch: Strip guess_unwinder out from prologue_unwinder
Date:   Thu, 12 Jan 2023 08:36:26 +0800
Message-Id: <20230112003627.26111-5-hejinyang@loongson.cn>
In-Reply-To: <20230112003627.26111-1-hejinyang@loongson.cn>
References: <20230112003627.26111-1-hejinyang@loongson.cn>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The prolugue unwinder rely on symbol info. When PC is not in kernel
text address, it cannot find relative symbol info and it will be broken.
The guess unwinder will be used in this case. And the guess unwinder
codes in prolugue unwinder is redundant. Strip it out and set the
unwinder type in unwind_state. Make guess_unwinder::unwind_next_frame()
as default way when other unwinders cannot unwind in some extreme case.

Signed-off-by: Jinyang He <hejinyang@loongson.cn>
---
 arch/loongarch/include/asm/unwind.h     |  29 +++++
 arch/loongarch/kernel/Makefile          |   2 +-
 arch/loongarch/kernel/traps.c           |   3 -
 arch/loongarch/kernel/unwind.c          |  33 +++++
 arch/loongarch/kernel/unwind_guess.c    |  51 +-------
 arch/loongarch/kernel/unwind_prologue.c | 153 ++++++++++--------------
 6 files changed, 129 insertions(+), 142 deletions(-)
 create mode 100644 arch/loongarch/kernel/unwind.c

diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
index 6ece48f0ff77..cb428e1b19af 100644
--- a/arch/loongarch/include/asm/unwind.h
+++ b/arch/loongarch/include/asm/unwind.h
@@ -27,6 +27,8 @@ struct unwind_state {
 	unsigned long sp, pc, ra;
 };
 
+extern bool default_next_frame(struct unwind_state *state);
+
 void unwind_start(struct unwind_state *state,
 		  struct task_struct *task, struct pt_regs *regs);
 bool unwind_next_frame(struct unwind_state *state);
@@ -49,4 +51,31 @@ static inline unsigned long unwind_graph_addr(struct unwind_state *state,
 	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
 				     pc, (unsigned long *)(cfa - GRAPH_FAKE_OFFSET));
 }
+
+static __always_inline void __unwind_start(struct unwind_state *state,
+					struct task_struct *task, struct pt_regs *regs)
+{
+	memset(state, 0, sizeof(*state));
+	if (regs) {
+		state->sp = regs->regs[3];
+		state->pc = regs->csr_era;
+		state->ra = regs->regs[1];
+	} else if (task == current || task == NULL) {
+		state->sp = (unsigned long)__builtin_frame_address(0);
+		state->pc = (unsigned long)__builtin_return_address(0);
+		state->ra = 0;
+	} else {
+		state->sp = thread_saved_fp(task);
+		state->pc = thread_saved_ra(task);
+		state->ra = 0;
+	}
+	state->task = task;
+	get_stack_info(state->sp, state->task, &state->stack_info);
+	state->pc = unwind_graph_addr(state, state->pc, state->sp);
+}
+
+static inline unsigned long __unwind_get_return_address(struct unwind_state *state)
+{
+	return unwind_done(state) ? 0 : state->pc;
+}
 #endif /* _ASM_UNWIND_H */
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index fcaa024a685e..c8cfbd562921 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -8,7 +8,7 @@ extra-y		:= vmlinux.lds
 obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
 		   traps.o irq.o idle.o process.o dma.o mem.o io.o reset.o switch.o \
 		   elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o \
-		   alternative.o unaligned.o
+		   alternative.o unaligned.o unwind.o
 
 obj-$(CONFIG_ACPI)		+= acpi.o
 obj-$(CONFIG_EFI) 		+= efi.o
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index a19bb329123b..8029757c50bd 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -72,9 +72,6 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
 	if (!task)
 		task = current;
 
-	if (user_mode(regs))
-		state.type = UNWINDER_GUESS;
-
 	printk("%sCall Trace:", loglvl);
 	for (unwind_start(&state, task, pregs);
 	      !unwind_done(&state); unwind_next_frame(&state)) {
diff --git a/arch/loongarch/kernel/unwind.c b/arch/loongarch/kernel/unwind.c
new file mode 100644
index 000000000000..58a5051f1797
--- /dev/null
+++ b/arch/loongarch/kernel/unwind.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022-2023 Loongson Technology Corporation Limited
+ */
+#include <linux/kernel.h>
+#include <linux/ftrace.h>
+
+#include <asm/unwind.h>
+
+bool default_next_frame(struct unwind_state *state)
+{
+	struct stack_info *info = &state->stack_info;
+	unsigned long addr;
+
+	if (unwind_done(state))
+		return false;
+
+	do {
+		for (state->sp += sizeof(unsigned long);
+		     state->sp < info->end;
+		     state->sp += sizeof(unsigned long)) {
+			addr = *(unsigned long *)(state->sp);
+			state->pc = unwind_graph_addr(state, addr, state->sp + 8);
+			if (__kernel_text_address(state->pc))
+				return true;
+		}
+
+		state->sp = info->next_sp;
+
+	} while (!get_stack_info(state->sp, state->task, info));
+
+	return false;
+}
diff --git a/arch/loongarch/kernel/unwind_guess.c b/arch/loongarch/kernel/unwind_guess.c
index 935d24f8c95c..98379b7d4147 100644
--- a/arch/loongarch/kernel/unwind_guess.c
+++ b/arch/loongarch/kernel/unwind_guess.c
@@ -2,40 +2,18 @@
 /*
  * Copyright (C) 2022 Loongson Technology Corporation Limited
  */
-#include <linux/kernel.h>
-#include <linux/ftrace.h>
-
 #include <asm/unwind.h>
 
 unsigned long unwind_get_return_address(struct unwind_state *state)
 {
-	if (unwind_done(state))
-		return 0;
-	return state->pc;
+	return __unwind_get_return_address(state);
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
 void unwind_start(struct unwind_state *state, struct task_struct *task,
 		    struct pt_regs *regs)
 {
-	memset(state, 0, sizeof(*state));
-
-	if (regs) {
-		state->sp = regs->regs[3];
-		state->pc = regs->csr_era;
-	} else if (task == current || task == NULL) {
-		state->sp = (unsigned long)__builtin_frame_address(0);
-		state->pc = (unsigned long)__builtin_return_address(0);
-	} else {
-		state->sp = thread_saved_fp(task);
-		state->pc = thread_saved_ra(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);
-
+	__unwind_start(state, task, regs);
 	if (!unwind_done(state) && !__kernel_text_address(state->pc))
 		unwind_next_frame(state);
 }
@@ -43,29 +21,6 @@ EXPORT_SYMBOL_GPL(unwind_start);
 
 bool unwind_next_frame(struct unwind_state *state)
 {
-	struct stack_info *info = &state->stack_info;
-	unsigned long addr;
-
-	if (unwind_done(state))
-		return false;
-
-	if (state->first)
-		state->first = false;
-
-	do {
-		for (state->sp += sizeof(unsigned long);
-		     state->sp < info->end;
-		     state->sp += sizeof(unsigned long)) {
-			addr = *(unsigned long *)(state->sp);
-			state->pc = unwind_graph_addr(state, addr, state->sp + 8);
-			if (__kernel_text_address(state->pc))
-				return true;
-		}
-
-		state->sp = info->next_sp;
-
-	} while (!get_stack_info(state->sp, state->task, info));
-
-	return false;
+	return default_next_frame(state);
 }
 EXPORT_SYMBOL_GPL(unwind_next_frame);
diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
index f7994ed05f04..e6c3f2ee507c 100644
--- a/arch/loongarch/kernel/unwind_prologue.c
+++ b/arch/loongarch/kernel/unwind_prologue.c
@@ -19,31 +19,14 @@ static inline void unwind_state_fixup(struct unwind_state *state)
 #endif
 }
 
-unsigned long unwind_get_return_address(struct unwind_state *state)
-{
-	if (unwind_done(state))
-		return 0;
-	return state->pc;
-}
-EXPORT_SYMBOL_GPL(unwind_get_return_address);
-
-static bool unwind_by_guess(struct unwind_state *state)
-{
-	struct stack_info *info = &state->stack_info;
-	unsigned long addr;
-
-	for (state->sp += sizeof(unsigned long);
-	     state->sp < info->end;
-	     state->sp += sizeof(unsigned long)) {
-		addr = *(unsigned long *)(state->sp);
-		state->pc = unwind_graph_addr(state, addr, state->sp + 8);
-		if (__kernel_text_address(state->pc))
-			return true;
-	}
-
-	return false;
-}
-
+/*
+ * LoongArch function prologue like follows,
+ *     [others instructions not use stack var]
+ *     addi.d sp, sp, -imm
+ *     st.d   xx, sp, offset <- save callee saved regs and
+ *     st.d   yy, sp, offset    save ra if function is nest.
+ *     [others instructions]
+ */
 static bool unwind_by_prologue(struct unwind_state *state)
 {
 	long frame_ra = -1;
@@ -89,6 +72,10 @@ static bool unwind_by_prologue(struct unwind_state *state)
 		ip++;
 	}
 
+	/*
+	 * Not find stack alloc action, PC may be in a leaf function. Only the
+	 * first being true is reasonable, otherwise indicate analysis is broken.
+	 */
 	if (!frame_size) {
 		if (state->first)
 			goto first;
@@ -106,6 +93,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
 		ip++;
 	}
 
+	/* Not find save $ra action, PC may be in a leaf function, too. */
 	if (frame_ra < 0) {
 		if (state->first) {
 			state->sp = state->sp + frame_size;
@@ -114,58 +102,20 @@ static bool unwind_by_prologue(struct unwind_state *state)
 		return false;
 	}
 
-	if (state->first)
-		state->first = false;
-
 	state->pc = *(unsigned long *)(state->sp + frame_ra);
 	state->sp = state->sp + frame_size;
 	goto out;
 
 first:
-	state->first = false;
-	if (state->pc == state->ra)
-		return false;
-
 	state->pc = state->ra;
 
 out:
+	state->first = false;
 	unwind_state_fixup(state);
 	return !!__kernel_text_address(state->pc);
 }
 
-void unwind_start(struct unwind_state *state, struct task_struct *task,
-		    struct pt_regs *regs)
-{
-	memset(state, 0, sizeof(*state));
-	state->type = UNWINDER_PROLOGUE;
-
-	if (regs) {
-		state->sp = regs->regs[3];
-		state->pc = regs->csr_era;
-		state->ra = regs->regs[1];
-		if (!__kernel_text_address(state->pc))
-			state->type = UNWINDER_GUESS;
-	} else if (task == current || task == NULL) {
-		state->sp = (unsigned long)__builtin_frame_address(0);
-		state->pc = (unsigned long)__builtin_return_address(0);
-		state->ra = 0;
-	} else {
-		state->sp = thread_saved_fp(task);
-		state->pc = thread_saved_ra(task);
-		state->ra = 0;
-	}
-
-	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))
-		unwind_next_frame(state);
-}
-EXPORT_SYMBOL_GPL(unwind_start);
-
-bool unwind_next_frame(struct unwind_state *state)
+static bool next_frame(struct unwind_state *state)
 {
 	struct stack_info *info = &state->stack_info;
 	struct pt_regs *regs;
@@ -175,35 +125,26 @@ bool unwind_next_frame(struct unwind_state *state)
 		return false;
 
 	do {
-		switch (state->type) {
-		case UNWINDER_GUESS:
-			state->first = false;
-			if (unwind_by_guess(state))
-				return true;
-			break;
-
-		case UNWINDER_PROLOGUE:
-			if (unwind_by_prologue(state)) {
-				state->pc = unwind_graph_addr(state, state->pc, state->sp);
-				return true;
-			}
+		if (unwind_by_prologue(state)) {
+			state->pc = unwind_graph_addr(state, state->pc, state->sp);
+			return true;
+		}
 
-			if (info->type == STACK_TYPE_IRQ &&
-				info->end == state->sp) {
-				regs = (struct pt_regs *)info->next_sp;
-				pc = regs->csr_era;
+		if (info->type == STACK_TYPE_IRQ &&
+		    info->end == state->sp) {
+			regs = (struct pt_regs *)info->next_sp;
+			pc = regs->csr_era;
 
-				if (user_mode(regs) || !__kernel_text_address(pc))
-					return false;
+			if (user_mode(regs) || !__kernel_text_address(pc))
+				return false;
 
-				state->first = true;
-				state->ra = regs->regs[1];
-				state->sp = regs->regs[3];
-				state->pc = pc;
-				get_stack_info(state->sp, state->task, info);
+			state->first = true;
+			state->ra = regs->regs[1];
+			state->sp = regs->regs[3];
+			state->pc = pc;
+			get_stack_info(state->sp, state->task, info);
 
-				return true;
-			}
+			return true;
 		}
 
 		state->sp = info->next_sp;
@@ -212,4 +153,36 @@ bool unwind_next_frame(struct unwind_state *state)
 
 	return false;
 }
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+	return __unwind_get_return_address(state);
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+		    struct pt_regs *regs)
+{
+	__unwind_start(state, task, regs);
+	state->type = UNWINDER_PROLOGUE;
+	state->first = true;
+
+	/*
+	 * The current PC is not kernel text address, we cannot find its
+	 * relative symbol. Thus, prologue analysis will be broken. Luckly,
+	 * we can use the default next_frame.
+	 */
+	if (!__kernel_text_address(state->pc)) {
+		state->type = UNWINDER_GUESS;
+		if (!unwind_done(state))
+			unwind_next_frame(state);
+	}
+}
+EXPORT_SYMBOL_GPL(unwind_start);
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+	return state->type == UNWINDER_PROLOGUE ?
+				next_frame(state) : default_next_frame(state);
+}
 EXPORT_SYMBOL_GPL(unwind_next_frame);
-- 
2.34.3