microblaze: Add stack unwinder
Implement intelligent backtracing by searching for stack frame creation,
and emitting only return addresses. Use print_hex_dump() to display the
entire binary kernel stack.
Limitation: MMU kernels are not currently able to trace beyond a system trap
(interrupt, syscall, etc.). It is the intent of this patch to provide
infrastructure that can be extended to add this capability later.
Changes from V1:
* Removed checks in find_frame_creation() that prevented location of the frame
creation instruction in heavily optimized code
* Various formatting/commenting/file location tweaks per review comments
* Dropped Kconfig option to enable STACKTRACE as something logically separate
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
diff --git a/arch/microblaze/kernel/unwind.c b/arch/microblaze/kernel/unwind.c
new file mode 100644
index 0000000..fefac5c
--- /dev/null
+++ b/arch/microblaze/kernel/unwind.c
@@ -0,0 +1,318 @@
+/*
+ * 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/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <asm/sections.h>
+#include <asm/exceptions.h>
+#include <asm/unwind.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
+ */
+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);
+
+/**
+ * unwind_trap - Unwind through a system trap, that stored previous state
+ * on the stack.
+ */
+#ifdef CONFIG_MMU
+static inline void unwind_trap(struct task_struct *task, unsigned long pc,
+ unsigned long fp, struct stack_trace *trace)
+{
+ /* To be implemented */
+}
+#else
+static inline void unwind_trap(struct task_struct *task, unsigned long pc,
+ unsigned long fp, struct stack_trace *trace)
+{
+ const struct pt_regs *regs = (const struct pt_regs *) fp;
+ microblaze_unwind_inner(task, regs->pc, regs->r1, regs->r15, trace);
+}
+#endif
+
+/**
+ * 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
+ */
+void microblaze_unwind_inner(struct task_struct *task,
+ unsigned long pc, unsigned long fp,
+ unsigned long leaf_return,
+ struct stack_trace *trace)
+{
+ 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()
+ */
+#ifndef CONFIG_MMU
+ const struct pt_regs *regs =
+ (const struct pt_regs *) fp;
+#endif
+ pr_info("HW EXCEPTION\n");
+#ifndef CONFIG_MMU
+ microblaze_unwind_inner(task, regs->r17 - 4,
+ fp + EX_HANDLER_STACK_SIZ,
+ regs->r15, trace);
+#endif
+ 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)
+ pr_info("%s\n", handler->trap_name);
+ unwind_trap(task, pc, fp, trace);
+ 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)) {
+ pr_info("[<%p>] PID %lu [%s]\n",
+ (void *) pc,
+ (unsigned long) task->pid,
+ task->comm);
+ break;
+ } else
+ print_ip_sym(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
+ */
+void microblaze_unwind(struct task_struct *task, struct stack_trace *trace)
+{
+ 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);
+ } 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);
+ }
+ } 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);
+ }
+}
+