mcount.c

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/*-
 * Copyright (c) 1983, 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include <sys/param.h>
#include <sys/gmon.h>
#ifdef _KERNEL
#ifndef GUPROF
#include <sys/systm.h>
#endif
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#endif

/*
 * mcount is called on entry to each function compiled with the profiling
 * switch set.  _mcount(), which is declared in a machine-dependent way
 * with _MCOUNT_DECL, does the actual work and is either inlined into a
 * C routine or called by an assembly stub.  In any case, this magic is
 * taken care of by the MCOUNT definition in <machine/profile.h>.
 *
 * _mcount updates data structures that represent traversals of the
 * program's call graph edges.  frompc and selfpc are the return
 * address and function address that represents the given call graph edge.
 *
 * Note: the original BSD code used the same variable (frompcindex) for
 * both frompcindex and frompc.  Any reasonable, modern compiler will
 * perform this optimization.
 */
_MCOUNT_DECL(frompc, selfpc)    /* _mcount; may be static, inline, etc */
        uintfptr_t frompc, selfpc;
{
#ifdef GUPROF
        int delta;
#endif
        fptrdiff_t frompci;
        u_short *frompcindex;
        struct tostruct *top, *prevtop;
        struct gmonparam *p;
        long toindex;
#ifdef _KERNEL
        MCOUNT_DECL(s)
#endif

        p = &_gmonparam;
#ifndef GUPROF                  /* XXX */
        /*
         * check that we are profiling
         * and that we aren't recursively invoked.
         */
        if (p->state != GMON_PROF_ON)
                return;
#endif
#ifdef _KERNEL
        MCOUNT_ENTER(s);
#else
        p->state = GMON_PROF_BUSY;
#endif

#ifdef _KERNEL
        /*
         * When we are called from an exception handler, frompc may be
         * a user address.  Convert such frompc's to some representation
         * in kernel address space.
         */
        frompc = MCOUNT_FROMPC_USER(frompc);
#endif

        frompci = frompc - p->lowpc;
        if (frompci >= p->textsize)
                goto done;

#ifdef GUPROF
        if (p->state == GMON_PROF_HIRES) {
                /*
                 * Count the time since cputime() was previously called
                 * against `frompc'.  Compensate for overheads.
                 *
                 * cputime() sets its prev_count variable to the count when
                 * it is called.  This in effect starts a counter for
                 * the next period of execution (normally from now until 
                 * the next call to mcount() or mexitcount()).  We set
                 * cputime_bias to compensate for our own overhead.
                 *
                 * We use the usual sampling counters since they can be
                 * located efficiently.  4-byte counters are usually
                 * necessary.  gprof will add up the scattered counts
                 * just like it does for statistical profiling.  All
                 * counts are signed so that underflow in the subtractions
                 * doesn't matter much (negative counts are normally
                 * compensated for by larger counts elsewhere).  Underflow
                 * shouldn't occur, but may be caused by slightly wrong
                 * calibrations or from not clearing cputime_bias.
                 */
                delta = cputime() - cputime_bias - p->mcount_pre_overhead;
                cputime_bias = p->mcount_post_overhead;
                KCOUNT(p, frompci) += delta;
                *p->cputime_count += p->cputime_overhead;
                *p->mcount_count += p->mcount_overhead;
        }
#endif /* GUPROF */

#ifdef _KERNEL
        /*
         * When we are called from an exception handler, frompc is faked
         * to be for where the exception occurred.  We've just solidified
         * the count for there.  Now convert frompci to an index that
         * represents the kind of exception so that interruptions appear
         * in the call graph as calls from those index instead of calls
         * from all over.
         */
        frompc = MCOUNT_FROMPC_INTR(selfpc);
        if ((frompc - p->lowpc) < p->textsize)
                frompci = frompc - p->lowpc;
#endif

        /*
         * check that frompc is a reasonable pc value.
         * for example: signal catchers get called from the stack,
         *              not from text space.  too bad.
         */
        if (frompci >= p->textsize)
                goto done;

        frompcindex = &p->froms[frompci / (p->hashfraction * sizeof(*p->froms))];
        toindex = *frompcindex;
        if (toindex == 0) {
                /*
                 *      first time traversing this arc
                 */
                toindex = ++p->tos[0].link;
                if (toindex >= p->tolimit)
                        /* halt further profiling */
                        goto overflow;

                *frompcindex = toindex;
                top = &p->tos[toindex];
                top->selfpc = selfpc;
                top->count = 1;
                top->link = 0;
                goto done;
        }
        top = &p->tos[toindex];
        if (top->selfpc == selfpc) {
                /*
                 * arc at front of chain; usual case.
                 */
                top->count++;
                goto done;
        }
        /*
         * have to go looking down chain for it.
         * top points to what we are looking at,
         * prevtop points to previous top.
         * we know it is not at the head of the chain.
         */
        for (; /* goto done */; ) {
                if (top->link == 0) {
                        /*
                         * top is end of the chain and none of the chain
                         * had top->selfpc == selfpc.
                         * so we allocate a new tostruct
                         * and link it to the head of the chain.
                         */
                        toindex = ++p->tos[0].link;
                        if (toindex >= p->tolimit)
                                goto overflow;

                        top = &p->tos[toindex];
                        top->selfpc = selfpc;
                        top->count = 1;
                        top->link = *frompcindex;
                        *frompcindex = toindex;
                        goto done;
                }
                /*
                 * otherwise, check the next arc on the chain.
                 */
                prevtop = top;
                top = &p->tos[top->link];
                if (top->selfpc == selfpc) {
                        /*
                         * there it is.
                         * increment its count
                         * move it to the head of the chain.
                         */
                        top->count++;
                        toindex = prevtop->link;
                        prevtop->link = top->link;
                        top->link = *frompcindex;
                        *frompcindex = toindex;
                        goto done;
                }

        }
done:
#ifdef _KERNEL
        MCOUNT_EXIT(s);
#else
        p->state = GMON_PROF_ON;
#endif
        return;
overflow:
        p->state = GMON_PROF_ERROR;
#ifdef _KERNEL
        MCOUNT_EXIT(s);
#endif
        return;
}

/*
 * Actual definition of mcount function.  Defined in <machine/profile.h>,
 * which is included by <sys/gmon.h>.
 */
MCOUNT

#ifdef GUPROF
void
mexitcount(selfpc)
        uintfptr_t selfpc;
{
        struct gmonparam *p;
        uintfptr_t selfpcdiff;

        p = &_gmonparam;
        selfpcdiff = selfpc - (uintfptr_t)p->lowpc;
        if (selfpcdiff < p->textsize) {
                int delta;

                /*
                 * Count the time since cputime() was previously called
                 * against `selfpc'.  Compensate for overheads.
                 */
                delta = cputime() - cputime_bias - p->mexitcount_pre_overhead;
                cputime_bias = p->mexitcount_post_overhead;
                KCOUNT(p, selfpcdiff) += delta;
                *p->cputime_count += p->cputime_overhead;
                *p->mexitcount_count += p->mexitcount_overhead;
        }
}

#ifndef __GNUCLIKE_ASM
#error "This file uses null asms to prevent timing loops being optimized away."
#endif

void
empty_loop()
{
        int i;

        for (i = 0; i < CALIB_SCALE; i++)
                __asm __volatile("");
}

void
nullfunc()
{
        __asm __volatile("");
}

void
nullfunc_loop()
{
        int i;

        for (i = 0; i < CALIB_SCALE; i++)
                nullfunc();
}
#endif /* GUPROF */