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    Subject[RFC Patch v1 42/55] ARC: stacktracing APIs based on dw2 unwinder
    Date
    From: Vineet Gupta <vgupta@synopsys.com>

    Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
    ---
    arch/arc/kernel/stacktrace.c | 215 +++++++++++++++++++++++++++++++++++++++++-
    1 files changed, 213 insertions(+), 2 deletions(-)

    diff --git a/arch/arc/kernel/stacktrace.c b/arch/arc/kernel/stacktrace.c
    index b9d1646..a63ff84 100644
    --- a/arch/arc/kernel/stacktrace.c
    +++ b/arch/arc/kernel/stacktrace.c
    @@ -1,13 +1,206 @@
    /*
    + * stacktrace.c : stacktracing APIs needed by rest of kernel
    + * (wrappers over ARC dwarf based unwinder)
    + *
    * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
    *
    * This program is free software; you can redistribute it and/or modify
    * it under the terms of the GNU General Public License version 2 as
    * published by the Free Software Foundation.
    + *
    + * vineetg: aug 2009
    + * -Implemented CONFIG_STACKTRACE APIs, primarily save_stack_trace_tsk( )
    + * for displaying task's kernel mode call stack in /proc/<pid>/stack
    + * -Iterator based approach to have single copy of unwinding core and APIs
    + * needing unwinding, implement the logic in iterator regarding:
    + * = which frame onwards to start capture
    + * = which frame to stop capturing (wchan)
    + * = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
    + *
    + * vineetg: March 2009
    + * -Implemented correct versions of thread_saved_pc() and get_wchan()
    + *
    + * rajeshwarr: 2008
    + * -Initial implementation
    */

    #include <linux/ptrace.h>
    #include <linux/export.h>
    +#include <linux/stacktrace.h>
    +#include <linux/kallsyms.h>
    +#include <asm/arcregs.h>
    +#include <asm/unwind.h>
    +#include <asm/switch_to.h>
    +
    +/*-------------------------------------------------------------------------
    + * Unwinder Iterator
    + *-------------------------------------------------------------------------
    + */
    +
    +#ifdef CONFIG_ARC_DW2_UNWIND
    +
    +static void seed_unwind_frame_info(struct task_struct *tsk,
    + struct pt_regs *regs,
    + struct unwind_frame_info *frame_info)
    +{
    + if (tsk == NULL && regs == NULL) {
    + unsigned long fp, sp, blink, ret;
    + frame_info->task = current;
    +
    + __asm__ __volatile__(
    + "mov %0,r27\n\t"
    + "mov %1,r28\n\t"
    + "mov %2,r31\n\t"
    + "mov %3,r63\n\t"
    + : "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
    + );
    +
    + frame_info->regs.r27 = fp;
    + frame_info->regs.r28 = sp;
    + frame_info->regs.r31 = blink;
    + frame_info->regs.r63 = ret;
    + frame_info->call_frame = 0;
    + } else if (regs == NULL) {
    +
    + frame_info->task = tsk;
    +
    + frame_info->regs.r27 = KSTK_FP(tsk);
    + frame_info->regs.r28 = KSTK_ESP(tsk);
    + frame_info->regs.r31 = KSTK_BLINK(tsk);
    + frame_info->regs.r63 = (unsigned int)__switch_to;
    +
    + /* In the prologue of __switch_to, first FP is saved on stack
    + * and then SP is copied to FP. Dwarf assumes cfa as FP based
    + * but we didn't save FP. The value retrieved above is FP's
    + * state in previous frame.
    + * As a work around for this, we unwind from __switch_to start
    + * and adjust SP accordingly. The other limitation is that
    + * __switch_to macro is dwarf rules are not generated for inline
    + * assembly code
    + */
    + frame_info->regs.r27 = 0;
    + frame_info->regs.r28 += 64;
    + frame_info->call_frame = 0;
    +
    + } else {
    + frame_info->task = tsk;
    +
    + frame_info->regs.r27 = regs->fp;
    + frame_info->regs.r28 = regs->sp;
    + frame_info->regs.r31 = regs->blink;
    + frame_info->regs.r63 = regs->ret;
    + frame_info->call_frame = 0;
    + }
    +}
    +
    +#endif
    +
    +static noinline unsigned int
    +arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
    + int (*consumer_fn) (unsigned int, void *), void *arg)
    +{
    +#ifdef CONFIG_ARC_DW2_UNWIND
    + int ret = 0;
    + unsigned int address;
    + struct unwind_frame_info frame_info;
    +
    + seed_unwind_frame_info(tsk, regs, &frame_info);
    +
    + while (1) {
    + address = UNW_PC(&frame_info);
    +
    + if (address && __kernel_text_address(address)) {
    + if (consumer_fn(address, arg) == -1)
    + break;
    + }
    +
    + ret = arc_unwind(&frame_info);
    +
    + if (ret == 0) {
    + frame_info.regs.r63 = frame_info.regs.r31;
    + continue;
    + } else {
    + break;
    + }
    + }
    +
    + return address; /* return the last address it saw */
    +#else
    + /* On ARC, only Dward based unwinder works. fp based backtracing is
    + * not possible (-fno-omit-frame-pointer) because of the way function
    + * prelogue is setup (callee regs saved and then fp set and not other
    + * way around
    + */
    + pr_warn("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
    + return 0;
    +
    +#endif
    +}
    +
    +/*-------------------------------------------------------------------------
    + * callbacks called by unwinder iterator to implement kernel APIs
    + *
    + * The callback can return -1 to force the iterator to stop, which by default
    + * keeps going till the bottom-most frame.
    + *-------------------------------------------------------------------------
    + */
    +
    +/* Call-back which plugs into unwinding core to dump the stack in
    + * case of panic/OOPs/BUG etc
    + */
    +static int __print_sym(unsigned int address, void *unused)
    +{
    + __print_symbol(" %s\n", address);
    + return 0;
    +}
    +
    +#ifdef CONFIG_STACKTRACE
    +
    +/* Call-back which plugs into unwinding core to capture the
    + * traces needed by kernel on /proc/<pid>/stack
    + */
    +static int __collect_all(unsigned int address, void *arg)
    +{
    + struct stack_trace *trace = arg;
    +
    + if (trace->skip > 0)
    + trace->skip--;
    + else
    + trace->entries[trace->nr_entries++] = address;
    +
    + if (trace->nr_entries >= trace->max_entries)
    + return -1;
    +
    + return 0;
    +}
    +
    +static int __collect_all_but_sched(unsigned int address, void *arg)
    +{
    + struct stack_trace *trace = arg;
    +
    + if (in_sched_functions(address))
    + return 0;
    +
    + if (trace->skip > 0)
    + trace->skip--;
    + else
    + trace->entries[trace->nr_entries++] = address;
    +
    + if (trace->nr_entries >= trace->max_entries)
    + return -1;
    +
    + return 0;
    +}
    +
    +#endif
    +
    +static int __get_first_nonsched(unsigned int address, void *unused)
    +{
    + if (in_sched_functions(address))
    + return 0;
    +
    + return -1;
    +}

    /*-------------------------------------------------------------------------
    * APIs expected by various kernel sub-systems
    @@ -16,7 +209,8 @@

    noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs)
    {
    - pr_info("\nStack Trace: NOT Available\n");
    + pr_info("\nStack Trace:\n");
    + arc_unwind_core(tsk, regs, __print_sym, NULL);
    }
    EXPORT_SYMBOL(show_stacktrace);

    @@ -39,5 +233,22 @@ EXPORT_SYMBOL(dump_stack);
    */
    unsigned int get_wchan(struct task_struct *tsk)
    {
    - return 0;
    + return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
    +}
    +
    +#ifdef CONFIG_STACKTRACE
    +
    +/*
    + * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
    + * A typical use is when /proc/<pid>/stack is queried by userland
    + */
    +void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
    +{
    + arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
    +}
    +
    +void save_stack_trace(struct stack_trace *trace)
    +{
    + arc_unwind_core(current, NULL, __collect_all, trace);
    }
    +#endif
    --
    1.7.4.1


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