backtrace.c

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#include <linux/oprofile.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <asm/ptrace.h>

/*
 * For IA64 we need to perform a complex little dance to get both
 * the struct pt_regs and a synthetic struct switch_stack in place
 * to allow the unwind code to work.  This dance requires our unwind
 * using code to be called from a function called from unw_init_running().
 * There we only get a single void* data pointer, so use this struct
 * to hold all the data we need during the unwind.
 */
typedef struct
{
    unsigned int depth;
    struct pt_regs *regs;
    struct unw_frame_info frame;
    unsigned long *prev_pfs_loc;    /* state for WAR for old spinlock ool code */
} ia64_backtrace_t;

/* Returns non-zero if the PC is in the Interrupt Vector Table */
static __inline__ int in_ivt_code(unsigned long pc)
{
    extern char ia64_ivt[];
    return (pc >= (u_long)ia64_ivt && pc < (u_long)ia64_ivt+32768);
}

/*
 * Unwind to next stack frame.
 */
static __inline__ int next_frame(ia64_backtrace_t *bt)
{
    /*
     * Avoid unsightly console message from unw_unwind() when attempting
     * to unwind through the Interrupt Vector Table which has no unwind
     * information.
     */
    if (in_ivt_code(bt->frame.ip))
        return 0;

    /*
     * WAR for spinlock contention from leaf functions.  ia64_spinlock_contention_pre3_4
     * has ar.pfs == r0.  Leaf functions do not modify ar.pfs so ar.pfs remains
     * as 0, stopping the backtrace.  Record the previous ar.pfs when the current
     * IP is in ia64_spinlock_contention_pre3_4 then unwind, if pfs_loc has not changed
     * after unwind then use pt_regs.ar_pfs which is where the real ar.pfs is for
     * leaf functions.
     */
    if (bt->prev_pfs_loc && bt->regs && bt->frame.pfs_loc == bt->prev_pfs_loc)
        bt->frame.pfs_loc = &bt->regs->ar_pfs;
    bt->prev_pfs_loc = NULL;

    return unw_unwind(&bt->frame) == 0;
}


static void do_ia64_backtrace(struct unw_frame_info *info, void *vdata)
{
    ia64_backtrace_t *bt = vdata;
    struct switch_stack *sw;
    int count = 0;
    u_long pc, sp;

    sw = (struct switch_stack *)(info+1);
    /* padding from unw_init_running */
    sw = (struct switch_stack *)(((unsigned long)sw + 15) & ~15);

    unw_init_frame_info(&bt->frame, current, sw);

    /* skip over interrupt frame and oprofile calls */
    do {
        unw_get_sp(&bt->frame, &sp);
        if (sp >= (u_long)bt->regs)
            break;
        if (!next_frame(bt))
            return;
    } while (count++ < 200);

    /* finally, grab the actual sample */
    while (bt->depth-- && next_frame(bt)) {
        unw_get_ip(&bt->frame, &pc);
        oprofile_add_trace(pc);
        if (unw_is_intr_frame(&bt->frame)) {
            /*
             * Interrupt received on kernel stack; this can
             * happen when timer interrupt fires while processing
             * a softirq from the tail end of a hardware interrupt
             * which interrupted a system call.  Don't laugh, it
             * happens!  Splice the backtrace into two parts to
             * avoid spurious cycles in the gprof output.
             */
            /* TODO: split rather than drop the 2nd half */
            break;
        }
    }
}

void
ia64_backtrace(struct pt_regs * const regs, unsigned int depth)
{
    ia64_backtrace_t bt;
    unsigned long flags;

    /*
     * On IA64 there is little hope of getting backtraces from
     * user space programs -- the problems of getting the unwind
     * information from arbitrary user programs are extreme.
     */
    if (user_mode(regs))
        return;

    bt.depth = depth;
    bt.regs = regs;
    bt.prev_pfs_loc = NULL;
    local_irq_save(flags);
    unw_init_running(do_ia64_backtrace, &bt);
    local_irq_restore(flags);
}