[PATCH 3/3] arm: Modify stack trace and dump for use with irq stack

[Maninder Singh <maninder1.s@samsung.com>]

This patch allows unwind_frame() to traverse from interrupt stack to task
stack correctly.

A similar approach is taken to modify dump_backtrace_entry(),
which expects to find struct pt_regs underneath any call to
functions marked __exception. When on an irq_stack,
the struct pt_regs is stored on the old task stack.

c_backtrace() is also modified on same logic, when traversing from last
IRQ frame, update fp with SVC mode fp.

Co-developed-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
---
 arch/arm/include/asm/irq.h   |  7 +++++++
 arch/arm/kernel/stacktrace.c | 21 ++++++++++++++++++++
 arch/arm/kernel/traps.c      | 47 +++++++++++++++++++++++++++++++++++++++++---
 arch/arm/lib/backtrace.S     | 18 +++++++++++++++++
 4 files changed, 90 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/irq.h b/arch/arm/include/asm/irq.h
index f3299ab..d4c66e9 100644
--- a/arch/arm/include/asm/irq.h
+++ b/arch/arm/include/asm/irq.h
@@ -30,6 +30,13 @@
 
 #ifdef CONFIG_IRQ_STACK
 DECLARE_PER_CPU(unsigned long *, irq_stack_ptr);
+
+#define IRQ_STACK_BASE_PTR	(unsigned long)(raw_cpu_read(irq_stack_ptr))
+#define IRQ_STACK_TOP_PTR	(unsigned long)(raw_cpu_read(irq_stack_ptr) + IRQ_STACK_SIZE)
+
+#define IRQ_STACK_TO_TASK_FRAME(ptr)	(*((unsigned long *)(ptr + 0x4)))
+#define IRQ_STACK_TO_TASK_STACK(ptr)	(*((unsigned long *)(ptr + 0x8)))
+
 #endif
 
 extern void asm_do_IRQ(unsigned int, struct pt_regs *);
diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index 76ea417..65b9634 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -7,6 +7,9 @@
 #include <asm/sections.h>
 #include <asm/stacktrace.h>
 #include <asm/traps.h>
+#ifdef CONFIG_IRQ_STACK
+#include <asm/irq.h>
+#endif
 
 #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
 /*
@@ -42,6 +45,13 @@ int notrace unwind_frame(struct stackframe *frame)
 {
 	unsigned long high, low;
 	unsigned long fp = frame->fp;
+#ifdef CONFIG_IRQ_STACK
+	unsigned long irq_stack_base_p;
+	unsigned long irq_stack_p;
+
+	irq_stack_base_p = IRQ_STACK_BASE_PTR;
+	irq_stack_p = irq_stack_base_p + IRQ_STACK_SIZE;
+#endif
 
 	/* only go to a higher address on the stack */
 	low = frame->sp;
@@ -67,6 +77,17 @@ int notrace unwind_frame(struct stackframe *frame)
 	frame->pc = *(unsigned long *)(fp - 4);
 #endif
 
+#ifdef CONFIG_IRQ_STACK
+	/*
+	 * Check whether we are going to walk through from interrupt stack
+	 * to task stack.
+	 * If we reach the end of the stack - and its an interrupt stack,
+	 * read the original task stack pointer base + 4 of IRQ stack.
+	 */
+	if (frame->sp == irq_stack_p)
+		frame->sp = IRQ_STACK_TO_TASK_STACK(irq_stack_base_p);
+#endif
+
 	return 0;
 }
 #endif
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 17d5a78..36b0cda 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -65,8 +65,20 @@ static int __init user_debug_setup(char *str)
 void dump_backtrace_entry(unsigned long where, unsigned long from,
 			  unsigned long frame, const char *loglvl)
 {
-	unsigned long end = frame + 4 + sizeof(struct pt_regs);
+	unsigned long end;
 
+#ifdef CONFIG_IRQ_STACK
+	unsigned long irq_stack_base_p;
+	unsigned long irq_stack_p;
+
+	irq_stack_base_p = IRQ_STACK_BASE_PTR;
+	irq_stack_p = irq_stack_base_p + IRQ_STACK_SIZE;
+
+	if (frame < irq_stack_p && (frame + sizeof(struct pt_regs)) > irq_stack_p)
+		frame = IRQ_STACK_TO_TASK_STACK(irq_stack_base_p) - 4;
+#endif
+
+	end = frame + 4 + sizeof(struct pt_regs);
 #ifdef CONFIG_KALLSYMS
 	printk("%s[<%08lx>] (%ps) from [<%08lx>] (%pS)\n",
 		loglvl, where, (void *)where, from, (void *)from);
@@ -113,6 +125,35 @@ static int verify_stack(unsigned long sp)
 
 	return 0;
 }
+
+#ifdef CONFIG_IRQ_STACK
+static int fp_underflow(unsigned long fp, struct task_struct *tsk)
+{
+	unsigned long end = (unsigned long)end_of_stack(tsk);
+	unsigned long irq_stack_base_p;
+	unsigned long irq_stack_p;
+
+	irq_stack_base_p = IRQ_STACK_BASE_PTR;
+	irq_stack_p = irq_stack_base_p + IRQ_STACK_SIZE;
+
+
+	if (fp > end && fp < end + THREAD_SIZE)
+		return 0;
+
+	if (fp > irq_stack_base_p && fp < irq_stack_p)
+		return 0;
+
+	return 1;
+}
+#else
+static int fp_underflow(unsigned long fp, struct task_struct *tsk)
+{
+	if (fp < (unsigned long)end_of_stack(tsk))
+		return 1;
+
+	return 0;
+}
+#endif
 #endif
 
 /*
@@ -238,7 +279,7 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 	} else if (verify_stack(fp)) {
 		pr_cont("invalid frame pointer 0x%08x", fp);
 		ok = 0;
-	} else if (fp < (unsigned long)end_of_stack(tsk))
+	} else if (fp_underflow(fp, tsk))
 		pr_cont("frame pointer underflow");
 	pr_cont("\n");
 
@@ -292,7 +333,7 @@ static int __die(const char *str, int err, struct pt_regs *regs)
 
 	if (!user_mode(regs) || in_interrupt()) {
 		dump_mem(KERN_EMERG, "Stack: ", regs->ARM_sp,
-			 THREAD_SIZE + (unsigned long)task_stack_page(tsk));
+			 THREAD_SIZE + (unsigned long)(regs->ARM_sp & ~(THREAD_SIZE - 1)));
 		dump_backtrace(regs, tsk, KERN_EMERG);
 		dump_instr(KERN_EMERG, regs);
 	}
diff --git a/arch/arm/lib/backtrace.S b/arch/arm/lib/backtrace.S
index 872f658..1a8e645 100644
--- a/arch/arm/lib/backtrace.S
+++ b/arch/arm/lib/backtrace.S
@@ -9,6 +9,9 @@
 #include <linux/kern_levels.h>
 #include <linux/linkage.h>
 #include <asm/assembler.h>
+#ifdef CONFIG_IRQ_STACK
+#include <asm/irq.h>
+#endif
 		.text
 
 @ fp is 0 or stack frame
@@ -96,6 +99,21 @@ for_each_frame:	tst	frame, mask		@ Check for address exceptions
 		teq	sv_fp, #0		@ zero saved fp means
 		beq	no_frame		@ no further frames
 
+#ifdef CONFIG_IRQ_STACK
+		/*
+		 * check if it is swtiching from IRQ to SVC,
+		 * then update frame accordingly.
+		 */
+		this_cpu_ptr irq_stack_ptr r2 r3
+		ldr	r3, [r2]
+		add	r2, r3, #IRQ_STACK_SIZE
+		ldr	r0, [frame, #-8]
+		cmp	r2, r0
+		ldreq	sv_fp, [r3, #4]
+		moveq	frame, sv_fp
+		beq	for_each_frame
+#endif
+
 		cmp	sv_fp, frame		@ next frame must be
 		mov	frame, sv_fp		@ above the current frame
 		bhi	for_each_frame
-- 
1.9.1