Re: [PATCH 1/3] LoongArch: Add guess unwinder support
From: Youling Tang
Date: Thu Jul 28 2022 - 22:01:53 EST
Hi, Qing
On 07/28/2022 10:05 PM, Qing Zhang wrote:
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@xxxxxxxxxxx>
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 26483e396ad1..33077010356d 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..ef2c3aeb1dab 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 +65,18 @@ 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;
+
+ unwind_start(&state, task, pregs);
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_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..7eeb3e1a989d
--- /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;
This judgment can be removed, because unwind_done() has been judged
before entering this function, and unwind_get_return_address will not
be called if it is true.
+ else if (state->first)
+ return state->pc;
+
+ return *(unsigned long *)(state->sp);
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+ struct stack_info *info = &state->stack_info;
+ unsigned long addr;
+
+ if (unwind_done(state))
+ return false;
+
Can be removed as above.
Thanks,
Youling
+ 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);
+
+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);