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From:   Qing Zhang <zhangqing@loongson.cn>
To:     Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        Jiaxun Yang <jiaxun.yang@flygoat.com>, hejinyang@loongson.cn
Subject: [PATCH 3/3] LoongArch: Add stacktrace support
Date:   Thu, 28 Jul 2022 22:05:19 +0800
Message-Id: <20220728140519.5420-3-zhangqing@loongson.cn>
In-Reply-To: <20220728140519.5420-1-zhangqing@loongson.cn>
References: <20220728140519.5420-1-zhangqing@loongson.cn>
MIME-Version: 1.0
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Use common arch_stack_walk infrastructure to avoid duplicated code and
avoid taking care of the stack storage and filtering.
Add sra (means __schedule return address) and scfa (means __schedule call
frame address) to thread_info and store it in switch_to().

Now we can print the process stack by cat /proc/*/stack and can better
support ftrace.

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

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index b57daee98b89..1bd656285674 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -38,6 +38,7 @@ config LOONGARCH
 	select ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE if !PREEMPTION
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_MIGHT_HAVE_PC_SERIO
+	select ARCH_STACKWALK
 	select ARCH_SPARSEMEM_ENABLE
 	select ARCH_SUPPORTS_ACPI
 	select ARCH_SUPPORTS_ATOMIC_RMW
@@ -141,6 +142,10 @@ config LOCKDEP_SUPPORT
 	bool
 	default y
 
+config STACKTRACE_SUPPORT
+	bool
+	default y
+
 # MACH_LOONGSON32 and MACH_LOONGSON64 are delibrately carried over from the
 # MIPS Loongson code, to preserve Loongson-specific code paths in drivers that
 # are shared between architectures, and specifically expecting the symbols.
diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
index 57ec45aa078e..1c4b4308378d 100644
--- a/arch/loongarch/include/asm/processor.h
+++ b/arch/loongarch/include/asm/processor.h
@@ -101,6 +101,10 @@ struct thread_struct {
 	unsigned long reg23, reg24, reg25, reg26; /* s0-s3 */
 	unsigned long reg27, reg28, reg29, reg30, reg31; /* s4-s8 */
 
+	/* __schedule() return address / call frame address */
+	unsigned long sched_ra;
+	unsigned long sched_cfa;
+
 	/* CSR registers */
 	unsigned long csr_prmd;
 	unsigned long csr_crmd;
@@ -129,6 +133,9 @@ struct thread_struct {
 	struct loongarch_fpu fpu FPU_ALIGN;
 };
 
+#define thread_saved_ra(tsk)	(tsk->thread.sched_ra)
+#define thread_saved_fp(tsk)	(tsk->thread.sched_cfa)
+
 #define INIT_THREAD  {						\
 	/*							\
 	 * Main processor registers				\
@@ -145,6 +152,8 @@ struct thread_struct {
 	.reg29			= 0,				\
 	.reg30			= 0,				\
 	.reg31			= 0,				\
+	.sched_ra		= 0,				\
+	.sched_cfa		= 0,				\
 	.csr_crmd		= 0,				\
 	.csr_prmd		= 0,				\
 	.csr_euen		= 0,				\
diff --git a/arch/loongarch/include/asm/switch_to.h b/arch/loongarch/include/asm/switch_to.h
index 2a8d04375574..836cfcc19498 100644
--- a/arch/loongarch/include/asm/switch_to.h
+++ b/arch/loongarch/include/asm/switch_to.h
@@ -15,12 +15,15 @@ struct task_struct;
  * @prev:	The task previously executed.
  * @next:	The task to begin executing.
  * @next_ti:	task_thread_info(next).
+ * @sched_ra:	__schedule return address.
+ * @sched_cfa:	__schedule call frame address.
  *
  * This function is used whilst scheduling to save the context of prev & load
  * the context of next. Returns prev.
  */
 extern asmlinkage struct task_struct *__switch_to(struct task_struct *prev,
-			struct task_struct *next, struct thread_info *next_ti);
+			struct task_struct *next, struct thread_info *next_ti,
+			void *sched_ra, void *sched_cfa);
 
 /*
  * For newly created kernel threads switch_to() will return to
@@ -31,7 +34,8 @@ extern asmlinkage struct task_struct *__switch_to(struct task_struct *prev,
 #define switch_to(prev, next, last)					\
 do {									\
 	lose_fpu_inatomic(1, prev);					\
-	(last) = __switch_to(prev, next, task_thread_info(next));	\
+	(last) = __switch_to(prev, next, task_thread_info(next),	\
+		 __builtin_return_address(0), __builtin_frame_address(0)); \
 } while (0)
 
 #endif /* _ASM_SWITCH_TO_H */
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 918600e7b30f..7449513eb08d 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_EFI) 		+= efi.o
 obj-$(CONFIG_CPU_HAS_FPU)	+= fpu.o
 
 obj-$(CONFIG_MODULES)		+= module.o module-sections.o
+obj-$(CONFIG_STACKTRACE)        += stacktrace.o
 
 obj-$(CONFIG_PROC_FS)		+= proc.o
 
diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c
index 20cd9e16a95a..eb350f3ffae5 100644
--- a/arch/loongarch/kernel/asm-offsets.c
+++ b/arch/loongarch/kernel/asm-offsets.c
@@ -103,6 +103,8 @@ void output_thread_defines(void)
 	OFFSET(THREAD_REG29, task_struct, thread.reg29);
 	OFFSET(THREAD_REG30, task_struct, thread.reg30);
 	OFFSET(THREAD_REG31, task_struct, thread.reg31);
+	OFFSET(THREAD_SCHED_RA, task_struct, thread.sched_ra);
+	OFFSET(THREAD_SCHED_CFA, task_struct, thread.sched_cfa);
 	OFFSET(THREAD_CSRCRMD, task_struct,
 	       thread.csr_crmd);
 	OFFSET(THREAD_CSRPRMD, task_struct,
diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
index 709b7a1664f8..34c3f2148714 100644
--- a/arch/loongarch/kernel/process.c
+++ b/arch/loongarch/kernel/process.c
@@ -135,6 +135,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	childregs = (struct pt_regs *) childksp - 1;
 	/*  Put the stack after the struct pt_regs.  */
 	childksp = (unsigned long) childregs;
+	p->thread.sched_cfa = 0;
 	p->thread.csr_euen = 0;
 	p->thread.csr_crmd = csr_read32(LOONGARCH_CSR_CRMD);
 	p->thread.csr_prmd = csr_read32(LOONGARCH_CSR_PRMD);
@@ -145,6 +146,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		p->thread.reg23 = (unsigned long)args->fn;
 		p->thread.reg24 = (unsigned long)args->fn_arg;
 		p->thread.reg01 = (unsigned long)ret_from_kernel_thread;
+		p->thread.sched_ra = (unsigned long)ret_from_kernel_thread;
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->csr_euen = p->thread.csr_euen;
 		childregs->csr_crmd = p->thread.csr_crmd;
@@ -161,6 +163,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 	p->thread.reg03 = (unsigned long) childregs;
 	p->thread.reg01 = (unsigned long) ret_from_fork;
+	p->thread.sched_ra = (unsigned long) ret_from_fork;
 
 	/*
 	 * New tasks lose permission to use the fpu. This accelerates context
diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
new file mode 100644
index 000000000000..f4f4b8ad3917
--- /dev/null
+++ b/arch/loongarch/kernel/stacktrace.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Stack trace management functions
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
+		     struct task_struct *task, struct pt_regs *regs)
+{
+	struct pt_regs dummyregs;
+	struct unwind_state state;
+	unsigned long addr;
+
+	regs = &dummyregs;
+
+	if (task == current) {
+		regs->csr_era = (unsigned long)__builtin_return_address(0);
+		regs->regs[3] = (unsigned long)__builtin_frame_address(0);
+	} else {
+		regs->csr_era = thread_saved_ra(task);
+		regs->regs[3] = thread_saved_fp(task);
+	}
+
+	regs->regs[1] = 0;
+	for (unwind_start(&state, task, regs);
+	      !unwind_done(&state); unwind_next_frame(&state)) {
+		addr = unwind_get_return_address(&state);
+		if (!addr || !consume_entry(cookie, addr))
+			break;
+	}
+}
diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
index 53e2fa8e580e..03d8c7add68f 100644
--- a/arch/loongarch/kernel/switch.S
+++ b/arch/loongarch/kernel/switch.S
@@ -21,6 +21,8 @@ SYM_FUNC_START(__switch_to)
 
 	cpu_save_nonscratch a0
 	stptr.d	ra, a0, THREAD_REG01
+	stptr.d a3, a0, THREAD_SCHED_RA
+	stptr.d a4, a0, THREAD_SCHED_CFA
 	move	tp, a2
 	cpu_restore_nonscratch a1
 
-- 
2.20.1