/*
* Backtrace support for Microblaze
*
* Copyright (C) 2010 Digital Design Corporation
*
* Based on arch/sh/kernel/cpu/sh5/unwind.c code which is:
* Copyright (C) 2004 Paul Mundt
* Copyright (C) 2004 Richard Curnow
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*/
/* #define DEBUG 1 */
#include <linux/export.h>
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/io.h>
#include <asm/sections.h>
#include <asm/exceptions.h>
#include <asm/unwind.h>
#include <asm/switch_to.h>
struct stack_trace;
/*
* On Microblaze, finding the previous stack frame is a little tricky.
* At this writing (3/2010), Microblaze does not support CONFIG_FRAME_POINTERS,
* and even if it did, gcc (4.1.2) does not store the frame pointer at
* a consistent offset within each frame. To determine frame size, it is
* necessary to search for the assembly instruction that creates or reclaims
* the frame and extract the size from it.
*
* Microblaze stores the stack pointer in r1, and creates a frame via
*
* addik r1, r1, -FRAME_SIZE
*
* The frame is reclaimed via
*
* addik r1, r1, FRAME_SIZE
*
* Frame creation occurs at or near the top of a function.
* Depending on the compiler, reclaim may occur at the end, or before
* a mid-function return.
*
* A stack frame is usually not created in a leaf function.
*
*/
/**
* get_frame_size - Extract the stack adjustment from an
* "addik r1, r1, adjust" instruction
* @instr : Microblaze instruction
*
* Return - Number of stack bytes the instruction reserves or reclaims
*/
static inline long get_frame_size(unsigned long instr)
{
return abs((s16)(instr & 0xFFFF));
}
/**
* find_frame_creation - Search backward to find the instruction that creates
* the stack frame (hopefully, for the same function the
* initial PC is in).
* @pc : Program counter at which to begin the search
*
* Return - PC at which stack frame creation occurs
* NULL if this cannot be found, i.e. a leaf function
*/
static unsigned long *find_frame_creation(unsigned long *pc)
{
int i;
/* NOTE: Distance to search is arbitrary
* 250 works well for most things,
* 750 picks up things like tcp_recvmsg(),
* 1000 needed for fat_fill_super()
*/
for (i = 0; i < 1000; i++, pc--) {
unsigned long instr;
s16 frame_size;
if (!kernel_text_address((unsigned long) pc))
return NULL;
instr = *pc;
/* addik r1, r1, foo ? */
if ((instr & 0xFFFF0000) != 0x30210000)
continue; /* No */
frame_size = get_frame_size(instr);
if ((frame_size < 8) || (frame_size & 3)) {
pr_debug(" Invalid frame size %d at 0x%p\n",
frame_size, pc);
return NULL;
}
pr_debug(" Found frame creation at 0x%p, size %d\n", pc,
frame_size);
return pc;
}
return NULL;
}
/**
* lookup_prev_stack_frame - Find the stack frame of the previous function.
* @fp : Frame (stack) pointer for current function
* @pc : Program counter within current function
* @leaf_return : r15 value within current function. If the current function
* is a leaf, this is the caller's return address.
* @pprev_fp : On exit, set to frame (stack) pointer for previous function
* @pprev_pc : On exit, set to current function caller's return address
*
* Return - 0 on success, -EINVAL if the previous frame cannot be found
*/
static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
unsigned long leaf_return,
unsigned long *pprev_fp,
unsigned long *pprev_pc)
{
unsigned long *prologue = NULL;
/* _switch_to is a special leaf function */
if (pc != (unsigned long) &_switch_to)
prologue = find_frame_creation((unsigned long *)pc);
if (prologue) {
long frame_size = get_frame_size(*prologue);
*pprev_fp = fp + frame_size;
*pprev_pc = *(unsigned long *)fp;
} else {
if (!leaf_return)
return -EINVAL;
*pprev_pc = leaf_return;
*pprev_fp = fp;
}
/* NOTE: don't check kernel_text_address here, to allow display
* of userland return address
*/
return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
}
static void microblaze_unwind_inner(struct task_struct *task,
unsigned long pc, unsigned long fp,
unsigned long leaf_return,
struct stack_trace *trace,
const char *loglvl);
/**
* unwind_trap - Unwind through a system trap, that stored previous state
* on the stack.
*/
static inline void unwind_trap(struct task_struct *task, unsigned long pc,
unsigned long fp, struct stack_trace *trace,
const char *loglvl)
{
/* To be implemented */
}
/**
* microblaze_unwind_inner - Unwind the stack from the specified point
* @task : Task whose stack we are to unwind (may be NULL)
* @pc : Program counter from which we start unwinding
* @fp : Frame (stack) pointer from which we start unwinding
* @leaf_return : Value of r15 at pc. If the function is a leaf, this is
* the caller's return address.
* @trace : Where to store stack backtrace (PC values).
* NULL == print backtrace to kernel log
* @loglvl : Used for printk log level if (trace == NULL).
*/
static void microblaze_unwind_inner(struct task_struct *task,
unsigned long pc, unsigned long fp,
unsigned long leaf_return,
struct stack_trace *trace,
const char *loglvl)
{
int ofs = 0;
pr_debug(" Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
if (!pc || !fp || (pc & 3) || (fp & 3)) {
pr_debug(" Invalid state for unwind, aborting\n");
return;
}
for (; pc != 0;) {
unsigned long next_fp, next_pc = 0;
unsigned long return_to = pc + 2 * sizeof(unsigned long);
const struct trap_handler_info *handler =
µblaze_trap_handlers;
/* Is previous function the HW exception handler? */
if ((return_to >= (unsigned long)&_hw_exception_handler)
&&(return_to < (unsigned long)&ex_handler_unhandled)) {
/*
* HW exception handler doesn't save all registers,
* so we open-code a special case of unwind_trap()
*/
printk("%sHW EXCEPTION\n", loglvl);
return;
}
/* Is previous function a trap handler? */
for (; handler->start_addr; ++handler) {
if ((return_to >= handler->start_addr)
&& (return_to <= handler->end_addr)) {
if (!trace)
printk("%s%s\n", loglvl, handler->trap_name);
unwind_trap(task, pc, fp, trace, loglvl);
return;
}
}
pc -= ofs;
if (trace) {
#ifdef CONFIG_STACKTRACE
if (trace->skip > 0)
trace->skip--;
else
trace->entries[trace->nr_entries++] = pc;
if (trace->nr_entries >= trace->max_entries)
break;
#endif
} else {
/* Have we reached userland? */
if (unlikely(pc == task_pt_regs(task)->pc)) {
printk("%s[<%p>] PID %lu [%s]\n",
loglvl, (void *) pc,
(unsigned long) task->pid,
task->comm);
break;
} else
print_ip_sym(loglvl, pc);
}
/* Stop when we reach anything not part of the kernel */
if (!kernel_text_address(pc))
break;
if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
&next_pc) == 0) {
ofs = sizeof(unsigned long);
pc = next_pc & ~3;
fp = next_fp;
leaf_return = 0;
} else {
pr_debug(" Failed to find previous stack frame\n");
break;
}
pr_debug(" Next PC=%p, next FP=%p\n",
(void *)next_pc, (void *)next_fp);
}
}
/**
* microblaze_unwind - Stack unwinder for Microblaze (external entry point)
* @task : Task whose stack we are to unwind (NULL == current)
* @trace : Where to store stack backtrace (PC values).
* NULL == print backtrace to kernel log
* @loglvl : Used for printk log level if (trace == NULL).
*/
void microblaze_unwind(struct task_struct *task, struct stack_trace *trace,
const char *loglvl)
{
if (task) {
if (task == current) {
const struct pt_regs *regs = task_pt_regs(task);
microblaze_unwind_inner(task, regs->pc, regs->r1,
regs->r15, trace, loglvl);
} else {
struct thread_info *thread_info =
(struct thread_info *)(task->stack);
const struct cpu_context *cpu_context =
&thread_info->cpu_context;
microblaze_unwind_inner(task,
(unsigned long) &_switch_to,
cpu_context->r1,
cpu_context->r15,
trace, loglvl);
}
} else {
unsigned long pc, fp;
__asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));
__asm__ __volatile__ (
"brlid %0, 0f;"
"nop;"
"0:"
: "=r" (pc)
);
/* Since we are not a leaf function, use leaf_return = 0 */
microblaze_unwind_inner(current, pc, fp, 0, trace, loglvl);
}
}