x86/dumpstack: Add get_stack_pointer() and get_frame_pointer()

The various functions involved in dumping the stack all do similar
things with regard to getting the stack pointer and the frame pointer
based on the regs and task arguments.  Create helper functions to
do that instead.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/f448914885a35f333fe04da1b97a6c2cc1f80974.1472057064.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/stacktrace.h

@@ -50,36 +50,41 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
 
 #ifdef CONFIG_X86_32
 #define STACKSLOTS_PER_LINE 8
-#define get_bp(bp) asm("movl %%ebp, %0" : "=r" (bp) :)
 #else
 #define STACKSLOTS_PER_LINE 4
-#define get_bp(bp) asm("movq %%rbp, %0" : "=r" (bp) :)
 #endif
 
 #ifdef CONFIG_FRAME_POINTER
-static inline unsigned long
-stack_frame(struct task_struct *task, struct pt_regs *regs)
+static inline unsigned long *
+get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 {
-	unsigned long bp;
-
 	if (regs)
-		return regs->bp;
+		return (unsigned long *)regs->bp;
 
-	if (task == current) {
-		/* Grab bp right from our regs */
-		get_bp(bp);
-		return bp;
-	}
+	if (!task || task == current)
+		return __builtin_frame_address(0);
 
-	return ((struct inactive_task_frame *)task->thread.sp)->bp;
+	return (unsigned long *)((struct inactive_task_frame *)task->thread.sp)->bp;
 }
 #else
-static inline unsigned long
-stack_frame(struct task_struct *task, struct pt_regs *regs)
+static inline unsigned long *
+get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 {
-	return 0;
+	return NULL;
+}
+#endif /* CONFIG_FRAME_POINTER */
+
+static inline unsigned long *
+get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
+{
+	if (regs)
+		return (unsigned long *)kernel_stack_pointer(regs);
+
+	if (!task || task == current)
+		return __builtin_frame_address(0);
+
+	return (unsigned long *)task->thread.sp;
 }
-#endif
 
 extern void
 show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
@@ -106,7 +111,7 @@ static inline unsigned long caller_frame_pointer(void)
 {
 	struct stack_frame *frame;
 
-	get_bp(frame);
+	frame = __builtin_frame_address(0);
 
 #ifdef CONFIG_FRAME_POINTER
 	frame = frame->next_frame;

arch/x86/kernel/dumpstack.c

@@ -170,15 +170,14 @@ show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 void show_stack(struct task_struct *task, unsigned long *sp)
 {
 	unsigned long bp = 0;
-	unsigned long stack;
 
 	/*
 	 * Stack frames below this one aren't interesting.  Don't show them
 	 * if we're printing for %current.
 	 */
 	if (!sp && (!task || task == current)) {
-		sp = &stack;
-		bp = stack_frame(current, NULL);
+		sp = get_stack_pointer(current, NULL);
+		bp = (unsigned long)get_frame_pointer(current, NULL);
 	}
 
 	show_stack_log_lvl(task, NULL, sp, bp, "");

arch/x86/kernel/dumpstack_32.c

@@ -46,19 +46,9 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 	int graph = 0;
 	u32 *prev_esp;
 
-	if (!task)
-		task = current;
-
-	if (!stack) {
-		unsigned long dummy;
-
-		stack = &dummy;
-		if (task != current)
-			stack = (unsigned long *)task->thread.sp;
-	}
-
-	if (!bp)
-		bp = stack_frame(task, regs);
+	task = task ? : current;
+	stack = stack ? : get_stack_pointer(task, regs);
+	bp = bp ? : (unsigned long)get_frame_pointer(task, regs);
 
 	for (;;) {
 		void *end_stack;
@@ -95,14 +85,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	unsigned long *stack;
 	int i;
 
-	if (sp == NULL) {
-		if (regs)
-			sp = (unsigned long *)regs->sp;
-		else if (task)
-			sp = (unsigned long *)task->thread.sp;
-		else
-			sp = (unsigned long *)&sp;
-	}
+	sp = sp ? : get_stack_pointer(task, regs);
 
 	stack = sp;
 	for (i = 0; i < kstack_depth_to_print; i++) {

arch/x86/kernel/dumpstack_64.c

@@ -151,25 +151,14 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 {
 	const unsigned cpu = get_cpu();
 	unsigned long *irq_stack = (unsigned long *)per_cpu(irq_stack_ptr, cpu);
-	unsigned long dummy;
 	unsigned used = 0;
 	int graph = 0;
 	int done = 0;
 
-	if (!task)
-		task = current;
+	task = task ? : current;
+	stack = stack ? : get_stack_pointer(task, regs);
+	bp = bp ? : (unsigned long)get_frame_pointer(task, regs);
 
-	if (!stack) {
-		if (regs)
-			stack = (unsigned long *)regs->sp;
-		else if (task != current)
-			stack = (unsigned long *)task->thread.sp;
-		else
-			stack = &dummy;
-	}
-
-	if (!bp)
-		bp = stack_frame(task, regs);
 	/*
 	 * Print function call entries in all stacks, starting at the
 	 * current stack address. If the stacks consist of nested
@@ -256,18 +245,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	irq_stack_end = (unsigned long *)(per_cpu(irq_stack_ptr, cpu));
 	irq_stack     = irq_stack_end - (IRQ_STACK_SIZE / sizeof(long));
 
-	/*
-	 * Debugging aid: "show_stack(NULL, NULL);" prints the
-	 * back trace for this cpu:
-	 */
-	if (sp == NULL) {
-		if (regs)
-			sp = (unsigned long *)regs->sp;
-		else if (task)
-			sp = (unsigned long *)task->thread.sp;
-		else
-			sp = (unsigned long *)&sp;
-	}
+	sp = sp ? : get_stack_pointer(task, regs);
 
 	stack = sp;
 	for (i = 0; i < kstack_depth_to_print; i++) {