unwind.c

  1/*
  2 * Backtrace support for Microblaze
  3 *
  4 * Copyright (C) 2010  Digital Design Corporation
  5 *
  6 * Based on arch/sh/kernel/cpu/sh5/unwind.c code which is:
  7 * Copyright (C) 2004  Paul Mundt
  8 * Copyright (C) 2004  Richard Curnow
  9 *
 10 * This file is subject to the terms and conditions of the GNU General Public
 11 * License.  See the file "COPYING" in the main directory of this archive
 12 * for more details.
 13 */
 14
 15/* #define DEBUG 1 */
 16#include <linux/export.h>
 17#include <linux/kallsyms.h>
 18#include <linux/kernel.h>
 19#include <linux/sched.h>
 20#include <linux/sched/task_stack.h>
 21#include <linux/stacktrace.h>
 22#include <linux/types.h>
 23#include <linux/errno.h>
 24#include <linux/io.h>
 25#include <asm/sections.h>
 26#include <asm/exceptions.h>
 27#include <asm/unwind.h>
 28#include <asm/switch_to.h>
 29
 30struct stack_trace;
 31
 32/*
 33 * On Microblaze, finding the previous stack frame is a little tricky.
 34 * At this writing (3/2010), Microblaze does not support CONFIG_FRAME_POINTERS,
 35 * and even if it did, gcc (4.1.2) does not store the frame pointer at
 36 * a consistent offset within each frame. To determine frame size, it is
 37 * necessary to search for the assembly instruction that creates or reclaims
 38 * the frame and extract the size from it.
 39 *
 40 * Microblaze stores the stack pointer in r1, and creates a frame via
 41 *
 42 *     addik r1, r1, -FRAME_SIZE
 43 *
 44 * The frame is reclaimed via
 45 *
 46 *     addik r1, r1, FRAME_SIZE
 47 *
 48 * Frame creation occurs at or near the top of a function.
 49 * Depending on the compiler, reclaim may occur at the end, or before
 50 * a mid-function return.
 51 *
 52 * A stack frame is usually not created in a leaf function.
 53 *
 54 */
 55
 56/**
 57 * get_frame_size - Extract the stack adjustment from an
 58 *                  "addik r1, r1, adjust" instruction
 59 * @instr : Microblaze instruction
 60 *
 61 * Return - Number of stack bytes the instruction reserves or reclaims
 62 */
 63static inline long get_frame_size(unsigned long instr)
 64{
 65	return abs((s16)(instr & 0xFFFF));
 66}
 67
 68/**
 69 * find_frame_creation - Search backward to find the instruction that creates
 70 *                       the stack frame (hopefully, for the same function the
 71 *                       initial PC is in).
 72 * @pc : Program counter at which to begin the search
 73 *
 74 * Return - PC at which stack frame creation occurs
 75 *          NULL if this cannot be found, i.e. a leaf function
 76 */
 77static unsigned long *find_frame_creation(unsigned long *pc)
 78{
 79	int i;
 80
 81	/* NOTE: Distance to search is arbitrary
 82	 *	 250 works well for most things,
 83	 *	 750 picks up things like tcp_recvmsg(),
 84	 *	1000 needed for fat_fill_super()
 85	 */
 86	for (i = 0; i < 1000; i++, pc--) {
 87		unsigned long instr;
 88		s16 frame_size;
 89
 90		if (!kernel_text_address((unsigned long) pc))
 91			return NULL;
 92
 93		instr = *pc;
 94
 95		/* addik r1, r1, foo ? */
 96		if ((instr & 0xFFFF0000) != 0x30210000)
 97			continue;	/* No */
 98
 99		frame_size = get_frame_size(instr);
100		if ((frame_size < 8) || (frame_size & 3)) {
101			pr_debug("    Invalid frame size %d at 0x%p\n",
102				 frame_size, pc);
103			return NULL;
104		}
105
106		pr_debug("    Found frame creation at 0x%p, size %d\n", pc,
107			 frame_size);
108		return pc;
109	}
110
111	return NULL;
112}
113
114/**
115 * lookup_prev_stack_frame - Find the stack frame of the previous function.
116 * @fp          : Frame (stack) pointer for current function
117 * @pc          : Program counter within current function
118 * @leaf_return : r15 value within current function. If the current function
119 *		  is a leaf, this is the caller's return address.
120 * @pprev_fp    : On exit, set to frame (stack) pointer for previous function
121 * @pprev_pc    : On exit, set to current function caller's return address
122 *
123 * Return - 0 on success, -EINVAL if the previous frame cannot be found
124 */
125static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
126				   unsigned long leaf_return,
127				   unsigned long *pprev_fp,
128				   unsigned long *pprev_pc)
129{
130	unsigned long *prologue = NULL;
131
132	/* _switch_to is a special leaf function */
133	if (pc != (unsigned long) &_switch_to)
134		prologue = find_frame_creation((unsigned long *)pc);
135
136	if (prologue) {
137		long frame_size = get_frame_size(*prologue);
138
139		*pprev_fp = fp + frame_size;
140		*pprev_pc = *(unsigned long *)fp;
141	} else {
142		if (!leaf_return)
143			return -EINVAL;
144		*pprev_pc = leaf_return;
145		*pprev_fp = fp;
146	}
147
148	/* NOTE: don't check kernel_text_address here, to allow display
149	 *	 of userland return address
150	 */
151	return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
152}
153
154static void microblaze_unwind_inner(struct task_struct *task,
155				    unsigned long pc, unsigned long fp,
156				    unsigned long leaf_return,
157				    struct stack_trace *trace,
158				    const char *loglvl);
159
160/**
161 * unwind_trap - Unwind through a system trap, that stored previous state
162 *		 on the stack.
163 */
164static inline void unwind_trap(struct task_struct *task, unsigned long pc,
165				unsigned long fp, struct stack_trace *trace,
166				const char *loglvl)
167{
168	/* To be implemented */
169}
170
171/**
172 * microblaze_unwind_inner - Unwind the stack from the specified point
173 * @task  : Task whose stack we are to unwind (may be NULL)
174 * @pc    : Program counter from which we start unwinding
175 * @fp    : Frame (stack) pointer from which we start unwinding
176 * @leaf_return : Value of r15 at pc. If the function is a leaf, this is
177 *				  the caller's return address.
178 * @trace : Where to store stack backtrace (PC values).
179 *	    NULL == print backtrace to kernel log
180 * @loglvl : Used for printk log level if (trace == NULL).
181 */
182static void microblaze_unwind_inner(struct task_struct *task,
183			     unsigned long pc, unsigned long fp,
184			     unsigned long leaf_return,
185			     struct stack_trace *trace,
186			     const char *loglvl)
187{
188	int ofs = 0;
189
190	pr_debug("    Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
191	if (!pc || !fp || (pc & 3) || (fp & 3)) {
192		pr_debug("    Invalid state for unwind, aborting\n");
193		return;
194	}
195	for (; pc != 0;) {
196		unsigned long next_fp, next_pc = 0;
197		unsigned long return_to = pc +  2 * sizeof(unsigned long);
198		const struct trap_handler_info *handler =
199			&microblaze_trap_handlers;
200
201		/* Is previous function the HW exception handler? */
202		if ((return_to >= (unsigned long)&_hw_exception_handler)
203		    &&(return_to < (unsigned long)&ex_handler_unhandled)) {
204			/*
205			 * HW exception handler doesn't save all registers,
206			 * so we open-code a special case of unwind_trap()
207			 */
208			printk("%sHW EXCEPTION\n", loglvl);
209			return;
210		}
211
212		/* Is previous function a trap handler? */
213		for (; handler->start_addr; ++handler) {
214			if ((return_to >= handler->start_addr)
215			    && (return_to <= handler->end_addr)) {
216				if (!trace)
217					printk("%s%s\n", loglvl, handler->trap_name);
218				unwind_trap(task, pc, fp, trace, loglvl);
219				return;
220			}
221		}
222		pc -= ofs;
223
224		if (trace) {
225#ifdef CONFIG_STACKTRACE
226			if (trace->skip > 0)
227				trace->skip--;
228			else
229				trace->entries[trace->nr_entries++] = pc;
230
231			if (trace->nr_entries >= trace->max_entries)
232				break;
233#endif
234		} else {
235			/* Have we reached userland? */
236			if (unlikely(pc == task_pt_regs(task)->pc)) {
237				printk("%s[<%p>] PID %lu [%s]\n",
238					loglvl, (void *) pc,
239					(unsigned long) task->pid,
240					task->comm);
241				break;
242			} else
243				print_ip_sym(loglvl, pc);
244		}
245
246		/* Stop when we reach anything not part of the kernel */
247		if (!kernel_text_address(pc))
248			break;
249
250		if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
251					    &next_pc) == 0) {
252			ofs = sizeof(unsigned long);
253			pc = next_pc & ~3;
254			fp = next_fp;
255			leaf_return = 0;
256		} else {
257			pr_debug("    Failed to find previous stack frame\n");
258			break;
259		}
260
261		pr_debug("    Next PC=%p, next FP=%p\n",
262			 (void *)next_pc, (void *)next_fp);
263	}
264}
265
266/**
267 * microblaze_unwind - Stack unwinder for Microblaze (external entry point)
268 * @task  : Task whose stack we are to unwind (NULL == current)
269 * @trace : Where to store stack backtrace (PC values).
270 *	    NULL == print backtrace to kernel log
271 * @loglvl : Used for printk log level if (trace == NULL).
272 */
273void microblaze_unwind(struct task_struct *task, struct stack_trace *trace,
274		       const char *loglvl)
275{
276	if (task) {
277		if (task == current) {
278			const struct pt_regs *regs = task_pt_regs(task);
279			microblaze_unwind_inner(task, regs->pc, regs->r1,
280						regs->r15, trace, loglvl);
281		} else {
282			struct thread_info *thread_info =
283				(struct thread_info *)(task->stack);
284			const struct cpu_context *cpu_context =
285				&thread_info->cpu_context;
286
287			microblaze_unwind_inner(task,
288						(unsigned long) &_switch_to,
289						cpu_context->r1,
290						cpu_context->r15,
291						trace, loglvl);
292		}
293	} else {
294		unsigned long pc, fp;
295
296		__asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));
297
298		__asm__ __volatile__ (
299			"brlid %0, 0f;"
300			"nop;"
301			"0:"
302			: "=r" (pc)
303		);
304
305		/* Since we are not a leaf function, use leaf_return = 0 */
306		microblaze_unwind_inner(current, pc, fp, 0, trace, loglvl);
307	}
308}
309