metag: Stack unwinding

Add stack unwinding support for metag.
Signed-off-by: James Hogan <james.hogan@imgtec.com>

arch/metag/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;
+};
+
+struct metag_frame {
+	unsigned long fp;
+	unsigned long lr;
+};
+
+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/metag/kernel/stacktrace.c

+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+
+#include <asm/stacktrace.h>
+
+#if defined(CONFIG_FRAME_POINTER)
+
+#ifdef CONFIG_KALLSYMS
+#include <linux/kallsyms.h>
+#include <linux/module.h>
+
+static unsigned long tbi_boing_addr;
+static unsigned long tbi_boing_size;
+
+static void tbi_boing_init(void)
+{
+	/* We need to know where TBIBoingVec is and it's size */
+	unsigned long size;
+	unsigned long offset;
+	char modname[MODULE_NAME_LEN];
+	char name[KSYM_NAME_LEN];
+	tbi_boing_addr = kallsyms_lookup_name("___TBIBoingVec");
+	if (!tbi_boing_addr)
+		tbi_boing_addr = 1;
+	else if (!lookup_symbol_attrs(tbi_boing_addr, &size,
+				      &offset, modname, name))
+		tbi_boing_size = size;
+}
+#endif
+
+#define ALIGN_DOWN(addr, size)  ((addr)&(~((size)-1)))
+
+/*
+ * 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.
+ */
+int notrace unwind_frame(struct stackframe *frame)
+{
+	struct metag_frame *fp = (struct metag_frame *)frame->fp;
+	unsigned long lr;
+	unsigned long fpnew;
+
+	if (frame->fp & 0x7)
+		return -EINVAL;
+
+	fpnew = fp->fp;
+	lr = fp->lr - 4;
+
+#ifdef CONFIG_KALLSYMS
+	/* If we've reached TBIBoingVec then we're at an interrupt
+	 * entry point or a syscall entry point. The frame pointer
+	 * points to a pt_regs which can be used to continue tracing on
+	 * the other side of the boing.
+	 */
+	if (!tbi_boing_addr)
+		tbi_boing_init();
+	if (tbi_boing_size && lr >= tbi_boing_addr &&
+	    lr < tbi_boing_addr + tbi_boing_size) {
+		struct pt_regs *regs = (struct pt_regs *)fpnew;
+		if (user_mode(regs))
+			return -EINVAL;
+		fpnew = regs->ctx.AX[1].U0;
+		lr = regs->ctx.DX[4].U1;
+	}
+#endif
+
+	/* stack grows up, so frame pointers must decrease */
+	if (fpnew < (ALIGN_DOWN((unsigned long)fp, THREAD_SIZE) +
+		     sizeof(struct thread_info)) || fpnew >= (unsigned long)fp)
+		return -EINVAL;
+
+	/* restore the registers from the stack frame */
+	frame->fp = fpnew;
+	frame->pc = lr;
+
+	return 0;
+}
+#else
+int notrace unwind_frame(struct stackframe *frame)
+{
+	struct metag_frame *sp = (struct metag_frame *)frame->sp;
+
+	if (frame->sp & 0x7)
+		return -EINVAL;
+
+	while (!kstack_end(sp)) {
+		unsigned long addr = sp->lr - 4;
+		sp--;
+
+		if (__kernel_text_address(addr)) {
+			frame->sp = (unsigned long)sp;
+			frame->pc = addr;
+			return 0;
+		}
+	}
+	return -EINVAL;
+}
+#endif
+
+void notrace walk_stackframe(struct stackframe *frame,
+		     int (*fn)(struct stackframe *, void *), void *data)
+{
+	while (1) {
+		int ret;
+
+		if (fn(frame, data))
+			break;
+		ret = unwind_frame(frame);
+		if (ret < 0)
+			break;
+	}
+}
+EXPORT_SYMBOL(walk_stackframe);
+
+#ifdef CONFIG_STACKTRACE
+struct stack_trace_data {
+	struct stack_trace *trace;
+	unsigned int no_sched_functions;
+	unsigned int skip;
+};
+
+static int save_trace(struct stackframe *frame, void *d)
+{
+	struct stack_trace_data *data = d;
+	struct stack_trace *trace = data->trace;
+	unsigned long addr = frame->pc;
+
+	if (data->no_sched_functions && in_sched_functions(addr))
+		return 0;
+	if (data->skip) {
+		data->skip--;
+		return 0;
+	}
+
+	trace->entries[trace->nr_entries++] = addr;
+
+	return trace->nr_entries >= trace->max_entries;
+}
+
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+	struct stack_trace_data data;
+	struct stackframe frame;
+
+	data.trace = trace;
+	data.skip = trace->skip;
+
+	if (tsk != current) {
+#ifdef CONFIG_SMP
+		/*
+		 * What guarantees do we have here that 'tsk' is not
+		 * running on another CPU?  For now, ignore it as we
+		 * can't guarantee we won't explode.
+		 */
+		if (trace->nr_entries < trace->max_entries)
+			trace->entries[trace->nr_entries++] = ULONG_MAX;
+		return;
+#else
+		data.no_sched_functions = 1;
+		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 ("A0StP");
+
+		data.no_sched_functions = 0;
+		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(&frame, save_trace, &data);
+	if (trace->nr_entries < trace->max_entries)
+		trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+
+void save_stack_trace(struct stack_trace *trace)
+{
+	save_stack_trace_tsk(current, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+#endif