microblaze: Add stack unwinder
Steven J. Magnani [Tue, 27 Apr 2010 17:37:54 +0000 (12:37 -0500)]
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>

arch/microblaze/include/asm/exceptions.h
arch/microblaze/include/asm/system.h
arch/microblaze/include/asm/unwind.h [new file with mode: 0644]
arch/microblaze/kernel/Makefile
arch/microblaze/kernel/entry-nommu.S
arch/microblaze/kernel/entry.S
arch/microblaze/kernel/hw_exception_handler.S
arch/microblaze/kernel/stacktrace.c
arch/microblaze/kernel/traps.c
arch/microblaze/kernel/unwind.c [new file with mode: 0644]

index 4c7b5d0..fa0e366 100644 (file)
 #define _ASM_MICROBLAZE_EXCEPTIONS_H
 
 #ifdef __KERNEL__
+
+#ifndef CONFIG_MMU
+#define EX_HANDLER_STACK_SIZ   (4*19)
+#endif
+
 #ifndef __ASSEMBLY__
 
 /* Macros to enable and disable HW exceptions in the MSR */
index 48c4f03..4f8eaea 100644 (file)
@@ -45,7 +45,6 @@ extern struct task_struct *_switch_to(struct thread_info *prev,
 #define smp_rmb()              rmb()
 #define smp_wmb()              wmb()
 
-void show_trace(struct task_struct *task, unsigned long *stack);
 void __bad_xchg(volatile void *ptr, int size);
 
 static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
diff --git a/arch/microblaze/include/asm/unwind.h b/arch/microblaze/include/asm/unwind.h
new file mode 100644 (file)
index 0000000..d248b7d
--- /dev/null
@@ -0,0 +1,29 @@
+/*
+ * Backtrace support for Microblaze
+ *
+ * Copyright (C) 2010  Digital Design Corporation
+ *
+ * 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.
+ */
+
+#ifndef __MICROBLAZE_UNWIND_H
+#define __MICROBLAZE_UNWIND_H
+
+struct stack_trace;
+
+struct trap_handler_info {
+       unsigned long start_addr;
+       unsigned long end_addr;
+       const char    *trap_name;
+};
+extern struct trap_handler_info microblaze_trap_handlers;
+
+extern const char _hw_exception_handler;
+extern const char ex_handler_unhandled;
+
+void microblaze_unwind(struct task_struct *task, struct stack_trace *trace);
+
+#endif /* __MICROBLAZE_UNWIND_H */
+
index e51bc15..d66ddef 100644 (file)
@@ -17,7 +17,7 @@ extra-y := head.o vmlinux.lds
 obj-y += dma.o exceptions.o \
        hw_exception_handler.o init_task.o intc.o irq.o of_device.o \
        of_platform.o process.o prom.o prom_parse.o ptrace.o \
-       setup.o signal.o sys_microblaze.o timer.o traps.o reset.o
+       reset.o setup.o signal.o sys_microblaze.o timer.o traps.o unwind.o
 
 obj-y += cpu/
 
index 8cc18cd..ca84368 100644 (file)
@@ -588,3 +588,31 @@ sys_rt_sigsuspend_wrapper:
 #include "syscall_table.S"
 
 syscall_table_size=(.-sys_call_table)
+
+type_SYSCALL:
+       .ascii "SYSCALL\0"
+type_IRQ:
+       .ascii "IRQ\0"
+type_IRQ_PREEMPT:
+       .ascii "IRQ (PREEMPTED)\0"
+type_SYSCALL_PREEMPT:
+       .ascii " SYSCALL (PREEMPTED)\0"
+
+       /*
+        * Trap decoding for stack unwinder
+        * Tuples are (start addr, end addr, string)
+        * If return address lies on [start addr, end addr],
+        * unwinder displays 'string'
+        */
+
+       .align 4
+.global microblaze_trap_handlers
+microblaze_trap_handlers:
+       /* Exact matches come first */
+       .word ret_to_user  ; .word ret_to_user    ; .word type_SYSCALL
+       .word ret_from_intr; .word ret_from_intr  ; .word type_IRQ
+       /* Fuzzy matches go here */
+       .word ret_from_intr; .word no_intr_resched; .word type_IRQ_PREEMPT
+       .word work_pending ; .word no_work_pending; .word type_SYSCALL_PREEMPT
+       /* End of table */
+       .word 0             ; .word 0               ; .word 0
index 077377a..7a19d89 100644 (file)
@@ -1127,3 +1127,30 @@ ENTRY(_break)
 
 syscall_table_size=(.-sys_call_table)
 
+type_SYSCALL:
+       .ascii "SYSCALL\0"
+type_IRQ:
+       .ascii "IRQ\0"
+type_IRQ_PREEMPT:
+       .ascii "IRQ (PREEMPTED)\0"
+type_SYSCALL_PREEMPT:
+       .ascii " SYSCALL (PREEMPTED)\0"
+
+       /*
+        * Trap decoding for stack unwinder
+        * Tuples are (start addr, end addr, string)
+        * If return address lies on [start addr, end addr],
+        * unwinder displays 'string'
+        */
+
+       .align 4
+.global microblaze_trap_handlers
+microblaze_trap_handlers:
+       /* Exact matches come first */
+       .word ret_from_trap; .word ret_from_trap   ; .word type_SYSCALL
+       .word ret_from_irq ; .word ret_from_irq    ; .word type_IRQ
+       /* Fuzzy matches go here */
+       .word ret_from_irq ; .word no_intr_resched ; .word type_IRQ_PREEMPT
+       .word ret_from_trap; .word TRAP_return     ; .word type_SYSCALL_PREEMPT
+       /* End of table */
+       .word 0               ; .word 0               ; .word 0
index 995a212..7811954 100644 (file)
@@ -78,9 +78,6 @@
 #include <asm/asm-offsets.h>
 
 /* Helpful Macros */
-#ifndef CONFIG_MMU
-#define EX_HANDLER_STACK_SIZ   (4*19)
-#endif
 #define NUM_TO_REG(num)                r ## num
 
 #ifdef CONFIG_MMU
@@ -988,6 +985,7 @@ ex_unaligned_fixup:
 .end _unaligned_data_exception
 #endif /* CONFIG_MMU */
 
+.global ex_handler_unhandled
 ex_handler_unhandled:
 /* FIXME add handle function for unhandled exception - dump register */
        bri 0
index 123692f..84bc668 100644 (file)
 #include <linux/thread_info.h>
 #include <linux/ptrace.h>
 #include <linux/module.h>
+#include <asm/unwind.h>
 
-/* FIXME initial support */
 void save_stack_trace(struct stack_trace *trace)
 {
-       unsigned long *sp;
-       unsigned long addr;
-       asm("addik %0, r1, 0" : "=r" (sp));
-
-       while (!kstack_end(sp)) {
-               addr = *sp++;
-               if (__kernel_text_address(addr)) {
-                       if (trace->skip > 0)
-                               trace->skip--;
-                       else
-                               trace->entries[trace->nr_entries++] = addr;
-
-                       if (trace->nr_entries >= trace->max_entries)
-                               break;
-               }
-       }
+       /* Exclude our helper functions from the trace*/
+       trace->skip += 2;
+       microblaze_unwind(NULL, trace);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace);
 
 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
-       unsigned int *sp;
-       unsigned long addr;
-
-       struct thread_info *ti = task_thread_info(tsk);
-
-       if (tsk == current)
-               asm("addik %0, r1, 0" : "=r" (sp));
-       else
-               sp = (unsigned int *)ti->cpu_context.r1;
-
-       while (!kstack_end(sp)) {
-               addr = *sp++;
-               if (__kernel_text_address(addr)) {
-                       if (trace->skip > 0)
-                               trace->skip--;
-                       else
-                               trace->entries[trace->nr_entries++] = addr;
-
-                       if (trace->nr_entries >= trace->max_entries)
-                               break;
-               }
-       }
+       microblaze_unwind(tsk, trace);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
index 75e4920..ba034d4 100644 (file)
 
 #include <asm/exceptions.h>
 #include <asm/system.h>
+#include <asm/unwind.h>
 
 void trap_init(void)
 {
        __enable_hw_exceptions();
 }
 
-static unsigned long kstack_depth_to_print = 24;
+static unsigned long kstack_depth_to_print;    /* 0 == entire stack */
 
 static int __init kstack_setup(char *s)
 {
@@ -30,31 +31,47 @@ static int __init kstack_setup(char *s)
 }
 __setup("kstack=", kstack_setup);
 
-void show_trace(struct task_struct *task, unsigned long *stack)
+void show_stack(struct task_struct *task, unsigned long *sp)
 {
-       unsigned long addr;
-
-       if (!stack)
-               stack = (unsigned long *)&stack;
+       unsigned long words_to_show;
+       u32 fp = (u32) sp;
+
+       if (fp == 0) {
+               if (task) {
+                       fp = ((struct thread_info *)
+                               (task->stack))->cpu_context.r1;
+               } else {
+                       /* Pick up caller of dump_stack() */
+                       fp = (u32)&sp - 8;
+               }
+       }
 
-       printk(KERN_NOTICE "Call Trace: ");
-#ifdef CONFIG_KALLSYMS
-       printk(KERN_NOTICE "\n");
-#endif
-       while (!kstack_end(stack)) {
-               addr = *stack++;
-               /*
-                * If the address is either in the text segment of the
-                * kernel, or in the region which contains vmalloc'ed
-                * memory, it *may* be the address of a calling
-                * routine; if so, print it so that someone tracing
-                * down the cause of the crash will be able to figure
-                * out the call path that was taken.
-                */
-               if (kernel_text_address(addr))
-                       print_ip_sym(addr);
+       words_to_show = (THREAD_SIZE - (fp & (THREAD_SIZE - 1))) >> 2;
+       if (kstack_depth_to_print && (words_to_show > kstack_depth_to_print))
+               words_to_show = kstack_depth_to_print;
+
+       pr_info("Kernel Stack:\n");
+
+       /*
+        * Make the first line an 'odd' size if necessary to get
+        * remaining lines to start at an address multiple of 0x10
+        */
+       if (fp & 0xF) {
+               unsigned long line1_words = (0x10 - (fp & 0xF)) >> 2;
+               if (line1_words < words_to_show) {
+                       print_hex_dump(KERN_INFO, "", DUMP_PREFIX_ADDRESS, 32,
+                                      4, (void *)fp, line1_words << 2, 0);
+                       fp += line1_words << 2;
+                       words_to_show -= line1_words;
+               }
        }
-       printk(KERN_NOTICE "\n");
+       print_hex_dump(KERN_INFO, "", DUMP_PREFIX_ADDRESS, 32, 4, (void *)fp,
+                      words_to_show << 2, 0);
+       printk(KERN_INFO "\n\n");
+
+       pr_info("Call Trace:\n");
+       microblaze_unwind(task, NULL);
+       pr_info("\n");
 
        if (!task)
                task = current;
@@ -62,34 +79,6 @@ void show_trace(struct task_struct *task, unsigned long *stack)
        debug_show_held_locks(task);
 }
 
-void show_stack(struct task_struct *task, unsigned long *sp)
-{
-       unsigned long *stack;
-       int i;
-
-       if (sp == NULL) {
-               if (task)
-                       sp = (unsigned long *) ((struct thread_info *)
-                                               (task->stack))->cpu_context.r1;
-               else
-                       sp = (unsigned long *)&sp;
-       }
-
-       stack = sp;
-
-       printk(KERN_INFO "\nStack:\n  ");
-
-       for (i = 0; i < kstack_depth_to_print; i++) {
-               if (kstack_end(sp))
-                       break;
-               if (i && ((i % 8) == 0))
-                       printk("\n  ");
-               printk("%08lx ", *sp++);
-       }
-       printk("\n");
-       show_trace(task, stack);
-}
-
 void dump_stack(void)
 {
        show_stack(NULL, NULL);
diff --git a/arch/microblaze/kernel/unwind.c b/arch/microblaze/kernel/unwind.c
new file mode 100644 (file)
index 0000000..fefac5c
--- /dev/null
@@ -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 =
+                       &microblaze_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);
+       }
+}
+