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mcount.c

/*-
 * 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.
 */

#if !defined(lint) && !defined(KERNEL) && defined(LIBC_SCCS)
static char sccsid[] = "@(#)mcount.c      8.1 (Berkeley) 6/4/93";
#endif

#include <unistd.h>
#include <sys/param.h>
#include <sys/gmon.h>

/* This file provides the machine-dependent definitions of the _MCOUNT_DECL
   and MCOUNT macros.  */
#include "machine-gmon.h"

#include <atomic.h>

/*
 * 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 */
{
      register ARCINDEX *frompcindex;
      register struct tostruct *top, *prevtop;
      register struct gmonparam *p;
      register ARCINDEX toindex;
      int i;

      p = &_gmonparam;
      /*
       * check that we are profiling
       * and that we aren't recursively invoked.
       */
      if (atomic_compare_and_exchange_bool_acq (&p->state, GMON_PROF_BUSY,
                                      GMON_PROF_ON))
        return;

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

      /* The following test used to be
            if (p->log_hashfraction >= 0)
         But we can simplify this if we assume the profiling data
         is always initialized by the functions in gmon.c.  But
         then it is possible to avoid a runtime check and use the
         smae `if' as in gmon.c.  So keep these tests in sync.  */
      if ((HASHFRACTION & (HASHFRACTION - 1)) == 0) {
        /* avoid integer divide if possible: */
          i = frompc >> p->log_hashfraction;
      } else {
          i = frompc / (p->hashfraction * sizeof(*p->froms));
      }
      frompcindex = &p->froms[i];
      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:
      p->state = GMON_PROF_ON;
      return;
overflow:
      p->state = GMON_PROF_ERROR;
      return;
}

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

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