[ARM] 5382/1: unwind: Reorganise the stacktrace support

This patch changes the walk_stacktrace and its callers for easier
integration of stack unwinding. The arch/arm/kernel/stacktrace.h file is
also moved to arch/arm/include/asm/stacktrace.h.

Signed-off-by: Catalin Marinas <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/stacktrace.h

···
+#ifndef __ASM_STACKTRACE_H
+#define __ASM_STACKTRACE_H
+
+struct stackframe {
+	unsigned long fp;
+	unsigned long sp;
+	unsigned long lr;
+	unsigned long pc;
+};
+
+extern int unwind_frame(struct stackframe *frame);
+extern void walk_stackframe(struct stackframe *frame,
+			    int (*fn)(struct stackframe *, void *), void *data);
+
+#endif	/* __ASM_STACKTRACE_H */

arch/arm/include/asm/thread_info.h

···
 
 #define thread_saved_pc(tsk)	\
 	((unsigned long)(task_thread_info(tsk)->cpu_context.pc))
+#define thread_saved_sp(tsk)	\
+	((unsigned long)(task_thread_info(tsk)->cpu_context.sp))
 #define thread_saved_fp(tsk)	\
 	((unsigned long)(task_thread_info(tsk)->cpu_context.fp))
 

arch/arm/kernel/process.c

···
 #include <asm/processor.h>
 #include <asm/system.h>
 #include <asm/thread_notify.h>
+#include <asm/stacktrace.h>
 #include <asm/mach/time.h>
 
 static const char *processor_modes[] = {
···
 
 unsigned long get_wchan(struct task_struct *p)
 {
-	unsigned long fp, lr;
-	unsigned long stack_start, stack_end;
+	struct stackframe frame;
 	int count = 0;
 	if (!p || p == current || p->state == TASK_RUNNING)
 		return 0;
 
-	stack_start = (unsigned long)end_of_stack(p);
-	stack_end = (unsigned long)task_stack_page(p) + THREAD_SIZE;
-
-	fp = thread_saved_fp(p);
+	frame.fp = thread_saved_fp(p);
+	frame.sp = thread_saved_sp(p);
+	frame.lr = 0;			/* recovered from the stack */
+	frame.pc = thread_saved_pc(p);
 	do {
-		if (fp < stack_start || fp > stack_end)
+		int ret = unwind_frame(&frame);
+		if (ret < 0)
 			return 0;
-		lr = ((unsigned long *)fp)[-1];
-		if (!in_sched_functions(lr))
-			return lr;
-		fp = *(unsigned long *) (fp - 12);
+		if (!in_sched_functions(frame.pc))
+			return frame.pc;
 	} while (count ++ < 16);
 	return 0;
 }

arch/arm/kernel/stacktrace.c

···
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
 
-#include "stacktrace.h"
+#include <asm/stacktrace.h>
 
-int walk_stackframe(unsigned long fp, unsigned long low, unsigned long high,
-		    int (*fn)(struct stackframe *, void *), void *data)
+#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
+/*
+ * Unwind the current stack frame and store the new register values in the
+ * structure passed as argument. Unwinding is equivalent to a function return,
+ * hence the new PC value rather than LR should be used for backtrace.
+ *
+ * With framepointer enabled, a simple function prologue looks like this:
+ *	mov	ip, sp
+ *	stmdb	sp!, {fp, ip, lr, pc}
+ *	sub	fp, ip, #4
+ *
+ * A simple function epilogue looks like this:
+ *	ldm	sp, {fp, sp, pc}
+ *
+ * Note that with framepointer enabled, even the leaf functions have the same
+ * prologue and epilogue, therefore we can ignore the LR value in this case.
+ */
+int unwind_frame(struct stackframe *frame)
 {
-	struct stackframe *frame;
+	unsigned long high, low;
+	unsigned long fp = frame->fp;
 
-	do {
-		/*
-		 * Check current frame pointer is within bounds
-		 */
-		if (fp < (low + 12) || fp + 4 >= high)
-			break;
+	/* only go to a higher address on the stack */
+	low = frame->sp;
+	high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;
 
-		frame = (struct stackframe *)(fp - 12);
+	/* check current frame pointer is within bounds */
+	if (fp < (low + 12) || fp + 4 >= high)
+		return -EINVAL;
+
+	/* restore the registers from the stack frame */
+	frame->fp = *(unsigned long *)(fp - 12);
+	frame->sp = *(unsigned long *)(fp - 8);
+	frame->pc = *(unsigned long *)(fp - 4);
+
+	return 0;
+}
+#endif
+
+void walk_stackframe(struct stackframe *frame,
+		     int (*fn)(struct stackframe *, void *), void *data)
+{
+	while (1) {
+		int ret;
 
 		if (fn(frame, data))
 			break;
-
-		/*
-		 * Update the low bound - the next frame must always
-		 * be at a higher address than the current frame.
-		 */
-		low = fp + 4;
-		fp = frame->fp;
-	} while (fp);
-
-	return 0;
+		ret = unwind_frame(frame);
+		if (ret < 0)
+			break;
+	}
 }
 EXPORT_SYMBOL(walk_stackframe);
 
···
 {
 	struct stack_trace_data *data = d;
 	struct stack_trace *trace = data->trace;
-	unsigned long addr = frame->lr;
+	unsigned long addr = frame->pc;
 
 	if (data->no_sched_functions && in_sched_functions(addr))
 		return 0;
···
 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
 	struct stack_trace_data data;
-	unsigned long fp, base;
+	struct stackframe frame;
 
 	data.trace = trace;
 	data.skip = trace->skip;
-	base = (unsigned long)task_stack_page(tsk);
 
 	if (tsk != current) {
 #ifdef CONFIG_SMP
···
 		BUG();
 #else
 		data.no_sched_functions = 1;
-		fp = thread_saved_fp(tsk);
+		frame.fp = thread_saved_fp(tsk);
+		frame.sp = thread_saved_sp(tsk);
+		frame.lr = 0;		/* recovered from the stack */
+		frame.pc = thread_saved_pc(tsk);
 #endif
 	} else {
+		register unsigned long current_sp asm ("sp");
+
 		data.no_sched_functions = 0;
-		asm("mov %0, fp" : "=r" (fp));
+		frame.fp = (unsigned long)__builtin_frame_address(0);
+		frame.sp = current_sp;
+		frame.lr = (unsigned long)__builtin_return_address(0);
+		frame.pc = (unsigned long)save_stack_trace_tsk;
 	}
 
-	walk_stackframe(fp, base, base + THREAD_SIZE, save_trace, &data);
+	walk_stackframe(&frame, save_trace, &data);
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }

arch/arm/kernel/stacktrace.h

···
-struct stackframe {
-	unsigned long fp;
-	unsigned long sp;
-	unsigned long lr;
-	unsigned long pc;
-};
-
-int walk_stackframe(unsigned long fp, unsigned long low, unsigned long high,
-		    int (*fn)(struct stackframe *, void *), void *data);

arch/arm/kernel/time.c

···
 
 #include <asm/leds.h>
 #include <asm/thread_info.h>
+#include <asm/stacktrace.h>
 #include <asm/mach/time.h>
 
 /*
···
 #ifdef CONFIG_SMP
 unsigned long profile_pc(struct pt_regs *regs)
 {
-	unsigned long fp, pc = instruction_pointer(regs);
+	struct stackframe frame;
 
-	if (in_lock_functions(pc)) {
-		fp = regs->ARM_fp;
-		pc = ((unsigned long *)fp)[-1];
-	}
+	if (!in_lock_functions(regs->ARM_pc))
+		return regs->ARM_pc;
 
-	return pc;
+	frame.fp = regs->ARM_fp;
+	frame.sp = regs->ARM_sp;
+	frame.lr = regs->ARM_lr;
+	frame.pc = regs->ARM_pc;
+	do {
+		int ret = unwind_frame(&frame);
+		if (ret < 0)
+			return 0;
+	} while (in_lock_functions(frame.pc));
+
+	return frame.pc;
 }
 EXPORT_SYMBOL(profile_pc);
 #endif

arch/arm/oprofile/backtrace.c

···
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 #include <asm/ptrace.h>
-
-#include "../kernel/stacktrace.h"
+#include <asm/stacktrace.h>
 
 static int report_trace(struct stackframe *frame, void *d)
 {
 	unsigned int *depth = d;
 
 	if (*depth) {
-		oprofile_add_trace(frame->lr);
+		oprofile_add_trace(frame->pc);
 		(*depth)--;
 	}
 
···
 	struct frame_tail *tail = ((struct frame_tail *) regs->ARM_fp) - 1;
 
 	if (!user_mode(regs)) {
-		unsigned long base = ((unsigned long)regs) & ~(THREAD_SIZE - 1);
-		walk_stackframe(regs->ARM_fp, base, base + THREAD_SIZE,
-				report_trace, &depth);
+		struct stackframe frame;
+		frame.fp = regs->ARM_fp;
+		frame.sp = regs->ARM_sp;
+		frame.lr = regs->ARM_lr;
+		frame.pc = regs->ARM_pc;
+		walk_stackframe(&frame, report_trace, &depth);
 		return;
 	}