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When mcount overflows, no gmon.out file is generated, but no message is printed
to the user, leaving the user with no idea why, and thinking maybe there is
some bug - which is how BZ 27576 ended up being logged. Print a message to
stderr in this case so the user knows what is going on.
As a comment in sys/gmon.h acknowledges, the hardcoded MAXARCS value is too
small for some large applications, including the test case in that BZ. Rather
than increase it, add tunables to enable MINARCS and MAXARCS to be overridden
at runtime (glibc.gmon.minarcs and glibc.gmon.maxarcs). So if a user gets the
mcount overflow error, they can try increasing maxarcs (they might need to
increase minarcs too if the heuristic is wrong in their case.)
Note setting minarcs/maxarcs too large can cause monstartup to fail with an
out of memory error. If you set them large enough, it can cause an integer
overflow in calculating the buffer size. I haven't done anything to defend
against that - it would not generally be a security vulnerability, since these
tunables will be ignored in suid/sgid programs (due to the SXID_ERASE default),
and if you can set GLIBC_TUNABLES in the environment of a process, you can take
it over anyway (LD_PRELOAD, LD_LIBRARY_PATH, etc). I thought about modifying
the code of monstartup to defend against integer overflows, but doing so is
complicated, and I realise the existing code is susceptible to them even prior
to this change (e.g. try passing a pathologically large highpc argument to
monstartup), so I decided just to leave that possibility in-place.
Add a test case which demonstrates mcount overflow and the tunables.
Document the new tunables in the manual.
Signed-off-by: Simon Kissane <skissane@gmail.com>
Reviewed-by: DJ Delorie <dj@redhat.com>
(cherry picked from commit 31be941e43)
204 lines
6.1 KiB
C
204 lines
6.1 KiB
C
/*-
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* Copyright (c) 1982, 1986, 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)gmon.h 8.2 (Berkeley) 1/4/94
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*/
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#ifndef _SYS_GMON_H
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#define _SYS_GMON_H 1
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#include <features.h>
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#include <sys/types.h>
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/*
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* See gmon_out.h for gmon.out format.
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*/
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/* structure emitted by "gcc -a". This must match struct bb in
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gcc/libgcc2.c. It is OK for gcc to declare a longer structure as
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long as the members below are present. */
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struct __bb
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{
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long zero_word;
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const char *filename;
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long *counts;
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long ncounts;
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struct __bb *next;
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const unsigned long *addresses;
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};
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extern struct __bb *__bb_head;
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/*
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* histogram counters are unsigned shorts (according to the kernel).
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*/
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#define HISTCOUNTER unsigned short
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/*
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* fraction of text space to allocate for histogram counters here, 1/2
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*/
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#define HISTFRACTION 2
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/*
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* Fraction of text space to allocate for from hash buckets.
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* The value of HASHFRACTION is based on the minimum number of bytes
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* of separation between two subroutine call points in the object code.
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* Given MIN_SUBR_SEPARATION bytes of separation the value of
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* HASHFRACTION is calculated as:
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*
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* HASHFRACTION = MIN_SUBR_SEPARATION / (2 * sizeof(short) - 1);
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*
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* For example, on the VAX, the shortest two call sequence is:
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*
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* calls $0,(r0)
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* calls $0,(r0)
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*
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* which is separated by only three bytes, thus HASHFRACTION is
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* calculated as:
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*
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* HASHFRACTION = 3 / (2 * 2 - 1) = 1
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*
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* Note that the division above rounds down, thus if MIN_SUBR_FRACTION
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* is less than three, this algorithm will not work!
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*
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* In practice, however, call instructions are rarely at a minimal
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* distance. Hence, we will define HASHFRACTION to be 2 across all
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* architectures. This saves a reasonable amount of space for
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* profiling data structures without (in practice) sacrificing
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* any granularity.
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*/
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#define HASHFRACTION 2
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/*
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* Percent of text space to allocate for tostructs.
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* This is a heuristic; we will fail with a warning when profiling programs
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* with a very large number of very small functions, but that's
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* normally OK.
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* 2 is probably still a good value for normal programs.
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* Profiling a test case with 64000 small functions will work if
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* you raise this value to 3 and link statically (which bloats the
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* text size, thus raising the number of arcs expected by the heuristic).
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*/
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#define ARCDENSITY 3
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/*
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* Always allocate at least this many tostructs. This
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* hides the inadequacy of the ARCDENSITY heuristic, at least
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* for small programs.
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*
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* Value can be overridden at runtime by glibc.gmon.minarcs tunable.
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*/
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#define MINARCS 50
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/*
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* The type used to represent indices into gmonparam.tos[].
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*/
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#define ARCINDEX unsigned long
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/*
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* Maximum number of arcs we want to allow.
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* Used to be max representable value of ARCINDEX minus 2, but now
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* that ARCINDEX is a long, that's too large; we don't really want
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* to allow a 48 gigabyte table.
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*
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* Value can be overridden at runtime by glibc.gmon.maxarcs tunable.
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*/
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#define MAXARCS (1 << 20)
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struct tostruct {
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unsigned long selfpc;
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long count;
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ARCINDEX link;
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};
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/*
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* a raw arc, with pointers to the calling site and
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* the called site and a count.
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*/
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struct rawarc {
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unsigned long raw_frompc;
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unsigned long raw_selfpc;
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long raw_count;
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};
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/*
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* general rounding functions.
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*/
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#define ROUNDDOWN(x,y) (((x)/(y))*(y))
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#define ROUNDUP(x,y) ((((x)+(y)-1)/(y))*(y))
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/*
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* The profiling data structures are housed in this structure.
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*/
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struct gmonparam {
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long int state;
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unsigned short *kcount;
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unsigned long kcountsize;
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ARCINDEX *froms;
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unsigned long fromssize;
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struct tostruct *tos;
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unsigned long tossize;
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long tolimit;
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unsigned long lowpc;
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unsigned long highpc;
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unsigned long textsize;
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unsigned long hashfraction;
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long log_hashfraction;
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};
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/*
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* Possible states of profiling.
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*/
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#define GMON_PROF_ON 0
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#define GMON_PROF_BUSY 1
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#define GMON_PROF_ERROR 2
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#define GMON_PROF_OFF 3
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/*
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* Sysctl definitions for extracting profiling information from the kernel.
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*/
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#define GPROF_STATE 0 /* int: profiling enabling variable */
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#define GPROF_COUNT 1 /* struct: profile tick count buffer */
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#define GPROF_FROMS 2 /* struct: from location hash bucket */
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#define GPROF_TOS 3 /* struct: destination/count structure */
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#define GPROF_GMONPARAM 4 /* struct: profiling parameters (see above) */
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__BEGIN_DECLS
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/* Set up data structures and start profiling. */
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extern void __monstartup (unsigned long __lowpc, unsigned long __highpc) __THROW;
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extern void monstartup (unsigned long __lowpc, unsigned long __highpc) __THROW;
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/* Clean up profiling and write out gmon.out. */
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extern void _mcleanup (void) __THROW;
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__END_DECLS
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#endif /* sys/gmon.h */
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