LoongArch: Add prologue unwinder support

It unwind the stack frame based on prologue code analyze.
CONFIG_KALLSYMS is needed, at least the address and length
of each function.

Three stages when we do unwind,
  1) unwind_start(), the prapare of unwinding, fill unwind_state.
  2) unwind_done(), judge whether the unwind process is finished or not.
  3) unwind_next_frame(), unwind the next frame.

Dividing unwinder helps to add new unwinders in the future, e.g.:
unwinder_frame, unwinder_orc, .etc.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig.debug

@@ -1,3 +1,11 @@
+choice
+	prompt "Choose kernel unwinder"
+	default UNWINDER_PROLOGUE if KALLSYMS
+	help
+	  This determines which method will be used for unwinding kernel stack
+	  traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
+	  lockdep, and more.
+
 config UNWINDER_GUESS
 	bool "Guess unwinder"
 	help
@@ -7,3 +15,15 @@ config UNWINDER_GUESS
 
 	  While this option often produces false positives, it can still be
 	  useful in many cases.
+
+config UNWINDER_PROLOGUE
+	bool "Prologue unwinder"
+	depends on KALLSYMS
+	help
+	  This option enables the "prologue" unwinder for unwinding kernel stack
+	  traces.  It unwind the stack frame based on prologue code analyze.  Symbol
+	  information is needed, at least the address and length of each function.
+	  Some of the addresses it reports may be incorrect (but better than the
+	  Guess unwinder).
+
+endchoice

arch/loongarch/include/asm/inst.h

@@ -23,12 +23,33 @@ enum reg1i20_op {
 	lu32id_op	= 0x0b,
 };
 
+enum reg1i21_op {
+	beqz_op		= 0x10,
+	bnez_op		= 0x11,
+};
+
 enum reg2i12_op {
+	addiw_op	= 0x0a,
+	addid_op	= 0x0b,
 	lu52id_op	= 0x0c,
+	ldb_op		= 0xa0,
+	ldh_op		= 0xa1,
+	ldw_op		= 0xa2,
+	ldd_op		= 0xa3,
+	stb_op		= 0xa4,
+	sth_op		= 0xa5,
+	stw_op		= 0xa6,
+	std_op		= 0xa7,
 };
 
 enum reg2i16_op {
 	jirl_op		= 0x13,
+	beq_op		= 0x16,
+	bne_op		= 0x17,
+	blt_op		= 0x18,
+	bge_op		= 0x19,
+	bltu_op		= 0x1a,
+	bgeu_op		= 0x1b,
 };
 
 struct reg0i26_format {
@@ -110,6 +131,37 @@ enum loongarch_gpr {
 	LOONGARCH_GPR_MAX
 };
 
+#define is_imm12_negative(val)	is_imm_negative(val, 12)
+
+static inline bool is_imm_negative(unsigned long val, unsigned int bit)
+{
+	return val & (1UL << (bit - 1));
+}
+
+static inline bool is_branch_ins(union loongarch_instruction *ip)
+{
+	return ip->reg1i21_format.opcode >= beqz_op &&
+		ip->reg1i21_format.opcode <= bgeu_op;
+}
+
+static inline bool is_ra_save_ins(union loongarch_instruction *ip)
+{
+	/* st.d $ra, $sp, offset */
+	return ip->reg2i12_format.opcode == std_op &&
+		ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
+		ip->reg2i12_format.rd == LOONGARCH_GPR_RA &&
+		!is_imm12_negative(ip->reg2i12_format.immediate);
+}
+
+static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
+{
+	/* addi.d $sp, $sp, -imm */
+	return ip->reg2i12_format.opcode == addid_op &&
+		ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
+		ip->reg2i12_format.rd == LOONGARCH_GPR_SP &&
+		is_imm12_negative(ip->reg2i12_format.immediate);
+}
+
 u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
 u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
 u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);

arch/loongarch/include/asm/unwind.h

@@ -11,11 +11,17 @@
 
 #include <asm/stacktrace.h>
 
+enum unwinder_type {
+	UNWINDER_GUESS,
+	UNWINDER_PROLOGUE,
+};
+
 struct unwind_state {
+	char type; /* UNWINDER_XXX */
 	struct stack_info stack_info;
 	struct task_struct *task;
 	bool first, error;
-	unsigned long sp, pc;
+	unsigned long sp, pc, ra;
 };
 
 void unwind_start(struct unwind_state *state,

arch/loongarch/kernel/Makefile

@@ -23,5 +23,6 @@ obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_NUMA)		+= numa.o
 
 obj-$(CONFIG_UNWINDER_GUESS)	+= unwind_guess.o
+obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
 
 CPPFLAGS_vmlinux.lds		:= $(KBUILD_CFLAGS)

arch/loongarch/kernel/traps.c

@@ -71,6 +71,9 @@ 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)) {

arch/loongarch/kernel/unwind_prologue.c

@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/kallsyms.h>
+
+#include <asm/inst.h>
+#include <asm/ptrace.h>
+#include <asm/unwind.h>
+
+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);
+
+}
+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);
+		if (__kernel_text_address(addr))
+			return true;
+	}
+
+	return false;
+}
+
+static bool unwind_by_prologue(struct unwind_state *state)
+{
+	struct stack_info *info = &state->stack_info;
+	union loongarch_instruction *ip, *ip_end;
+	unsigned long frame_size = 0, frame_ra = -1;
+	unsigned long size, offset, pc = state->pc;
+
+	if (state->sp >= info->end || state->sp < info->begin)
+		return false;
+
+	if (!kallsyms_lookup_size_offset(pc, &size, &offset))
+		return false;
+
+	ip = (union loongarch_instruction *)(pc - offset);
+	ip_end = (union loongarch_instruction *)pc;
+
+	while (ip < ip_end) {
+		if (is_stack_alloc_ins(ip)) {
+			frame_size = (1 << 12) - ip->reg2i12_format.immediate;
+			ip++;
+			break;
+		}
+		ip++;
+	}
+
+	if (!frame_size) {
+		if (state->first)
+			goto first;
+
+		return false;
+	}
+
+	while (ip < ip_end) {
+		if (is_ra_save_ins(ip)) {
+			frame_ra = ip->reg2i12_format.immediate;
+			break;
+		}
+		if (is_branch_ins(ip))
+			break;
+		ip++;
+	}
+
+	if (frame_ra < 0) {
+		if (state->first) {
+			state->sp = state->sp + frame_size;
+			goto first;
+		}
+		return false;
+	}
+
+	if (state->first)
+		state->first = false;
+
+	state->pc = *(unsigned long *)(state->sp + frame_ra);
+	state->sp = state->sp + frame_size;
+	return !!__kernel_text_address(state->pc);
+
+first:
+	state->first = false;
+	if (state->pc == state->ra)
+		return false;
+
+	state->pc = state->ra;
+
+	return !!__kernel_text_address(state->ra);
+}
+
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+		    struct pt_regs *regs)
+{
+	memset(state, 0, sizeof(*state));
+
+	if (regs &&  __kernel_text_address(regs->csr_era)) {
+		state->pc = regs->csr_era;
+		state->sp = regs->regs[3];
+		state->ra = regs->regs[1];
+		state->type = UNWINDER_PROLOGUE;
+	}
+
+	state->task = task;
+	state->first = true;
+
+	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)
+{
+	struct stack_info *info = &state->stack_info;
+	struct pt_regs *regs;
+	unsigned long pc;
+
+	if (unwind_done(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))
+				return true;
+
+			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;
+
+				state->pc = pc;
+				state->sp = regs->regs[3];
+				state->ra = regs->regs[1];
+				state->first = true;
+				get_stack_info(state->sp, state->task, info);
+
+				return true;
+			}
+		}
+
+		state->sp = info->next_sp;
+
+	} while (!get_stack_info(state->sp, state->task, info));
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);