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Subject[PATCH v3 1/4] LoongArch: Add guess unwinder support
Date
Name "guess unwinder" comes from x86, It scans the stack and reports
every kernel text address it finds.

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.

Make the dump_stack process go through unwind process.
Add get_stack_info() to get stack info. At present we have irq stack and
task stack. Maybe add another type in future. The next_sp means the key
info between this type stack and next type stack.

Dividing unwinder helps to add new unwinders in the future.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
---
arch/loongarch/Kconfig.debug | 9 ++++
arch/loongarch/include/asm/stacktrace.h | 17 +++++++
arch/loongarch/include/asm/unwind.h | 37 ++++++++++++++
arch/loongarch/kernel/Makefile | 2 +
arch/loongarch/kernel/process.c | 61 +++++++++++++++++++++++
arch/loongarch/kernel/traps.c | 21 ++++----
arch/loongarch/kernel/unwind_guess.c | 65 +++++++++++++++++++++++++
7 files changed, 201 insertions(+), 11 deletions(-)
create mode 100644 arch/loongarch/include/asm/unwind.h
create mode 100644 arch/loongarch/kernel/unwind_guess.c

diff --git a/arch/loongarch/Kconfig.debug b/arch/loongarch/Kconfig.debug
index e69de29bb2d1..68634d4fa27b 100644
--- a/arch/loongarch/Kconfig.debug
+++ b/arch/loongarch/Kconfig.debug
@@ -0,0 +1,9 @@
+config UNWINDER_GUESS
+ bool "Guess unwinder"
+ help
+ This option enables the "guess" unwinder for unwinding kernel stack
+ traces. It scans the stack and reports every kernel text address it
+ finds. Some of the addresses it reports may be incorrect.
+
+ While this option often produces false positives, it can still be
+ useful in many cases.
diff --git a/arch/loongarch/include/asm/stacktrace.h b/arch/loongarch/include/asm/stacktrace.h
index 6b5c2a7aa706..49cb89213aeb 100644
--- a/arch/loongarch/include/asm/stacktrace.h
+++ b/arch/loongarch/include/asm/stacktrace.h
@@ -10,6 +10,23 @@
#include <asm/loongarch.h>
#include <linux/stringify.h>

+enum stack_type {
+ STACK_TYPE_UNKNOWN,
+ STACK_TYPE_TASK,
+ STACK_TYPE_IRQ,
+};
+
+struct stack_info {
+ enum stack_type type;
+ unsigned long begin, end, next_sp;
+};
+
+bool in_task_stack(unsigned long stack, struct task_struct *task,
+ struct stack_info *info);
+bool in_irq_stack(unsigned long stack, struct stack_info *info);
+int get_stack_info(unsigned long stack, struct task_struct *task,
+ struct stack_info *info);
+
#define STR_LONG_L __stringify(LONG_L)
#define STR_LONG_S __stringify(LONG_S)
#define STR_LONGSIZE __stringify(LONGSIZE)
diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
new file mode 100644
index 000000000000..243330b39d0d
--- /dev/null
+++ b/arch/loongarch/include/asm/unwind.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Most of this ideas comes from x86.
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_UNWIND_H
+#define _ASM_UNWIND_H
+
+#include <linux/sched.h>
+
+#include <asm/stacktrace.h>
+
+struct unwind_state {
+ struct stack_info stack_info;
+ struct task_struct *task;
+ unsigned long sp, pc;
+ bool first;
+ bool error;
+};
+
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs);
+bool unwind_next_frame(struct unwind_state *state);
+unsigned long unwind_get_return_address(struct unwind_state *state);
+
+static inline bool unwind_done(struct unwind_state *state)
+{
+ return state->stack_info.type == STACK_TYPE_UNKNOWN;
+}
+
+static inline bool unwind_error(struct unwind_state *state)
+{
+ return state->error;
+}
+
+#endif /* _ASM_UNWIND_H */
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 940de9173542..c5fa4adb23b6 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -22,4 +22,6 @@ obj-$(CONFIG_SMP) += smp.o

obj-$(CONFIG_NUMA) += numa.o

+obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
+
CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
index bfa0dfe8b7d7..709b7a1664f8 100644
--- a/arch/loongarch/kernel/process.c
+++ b/arch/loongarch/kernel/process.c
@@ -44,6 +44,7 @@
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/reg.h>
+#include <asm/unwind.h>
#include <asm/vdso.h>

/*
@@ -183,6 +184,66 @@ unsigned long __get_wchan(struct task_struct *task)
return 0;
}

+bool in_task_stack(unsigned long stack, struct task_struct *task,
+ struct stack_info *info)
+{
+ unsigned long begin = (unsigned long)task_stack_page(task);
+ unsigned long end = begin + THREAD_SIZE - 32;
+
+ if (stack < begin || stack >= end)
+ return false;
+
+ info->type = STACK_TYPE_TASK;
+ info->begin = begin;
+ info->end = end;
+ info->next_sp = 0;
+
+ return true;
+}
+
+bool in_irq_stack(unsigned long stack, struct stack_info *info)
+{
+ unsigned long nextsp;
+ unsigned long begin = (unsigned long)this_cpu_read(irq_stack);
+ unsigned long end = begin + IRQ_STACK_START;
+
+ if (stack < begin || stack >= end)
+ return false;
+
+ nextsp = *(unsigned long *)end;
+ if (nextsp & (SZREG - 1))
+ return false;
+
+ info->type = STACK_TYPE_IRQ;
+ info->begin = begin;
+ info->end = end;
+ info->next_sp = nextsp;
+
+ return true;
+}
+
+int get_stack_info(unsigned long stack, struct task_struct *task,
+ struct stack_info *info)
+{
+ task = task ? : current;
+
+ if (!stack || stack & (SZREG - 1))
+ goto unknown;
+
+ if (in_task_stack(stack, task, info))
+ return 0;
+
+ if (task != current)
+ goto unknown;
+
+ if (in_irq_stack(stack, info))
+ return 0;
+
+unknown:
+ info->type = STACK_TYPE_UNKNOWN;
+ return -EINVAL;
+}
+
unsigned long stack_top(void)
{
unsigned long top = TASK_SIZE & PAGE_MASK;
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index 1bf58c65e2bf..f65fdf90d29e 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -43,6 +43,7 @@
#include <asm/stacktrace.h>
#include <asm/tlb.h>
#include <asm/types.h>
+#include <asm/unwind.h>

#include "access-helper.h"

@@ -64,19 +65,17 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
const char *loglvl, bool user)
{
unsigned long addr;
- unsigned long *sp = (unsigned long *)(regs->regs[3] & ~3);
+ struct unwind_state state;
+ struct pt_regs *pregs = (struct pt_regs *)regs;
+
+ if (!task)
+ task = current;

printk("%sCall Trace:", loglvl);
-#ifdef CONFIG_KALLSYMS
- printk("%s\n", loglvl);
-#endif
- while (!kstack_end(sp)) {
- if (__get_addr(&addr, sp++, user)) {
- printk("%s (Bad stack address)", loglvl);
- break;
- }
- if (__kernel_text_address(addr))
- print_ip_sym(loglvl, addr);
+ for (unwind_start(&state, task, pregs);
+ !unwind_done(&state); unwind_next_frame(&state)) {
+ addr = unwind_get_return_address(&state);
+ print_ip_sym(loglvl, addr);
}
printk("%s\n", loglvl);
}
diff --git a/arch/loongarch/kernel/unwind_guess.c b/arch/loongarch/kernel/unwind_guess.c
new file mode 100644
index 000000000000..71bad8a345a7
--- /dev/null
+++ b/arch/loongarch/kernel/unwind_guess.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/kernel.h>
+
+#include <asm/unwind.h>
+
+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);
+}
+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));
+
+ state->task = task;
+
+ state->sp = regs->regs[3];
+ state->pc = regs->csr_era;
+ 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;
+ 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);
+
+ if (__kernel_text_address(addr))
+ return true;
+ }
+
+ state->sp = info->next_sp;
+
+ } while (!get_stack_info(state->sp, state->task, info));
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
--
2.20.1
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