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IABSD.fr/src/lib/libc/sys/profil.2
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.\" $OpenBSD: profil.2,v 1.17 2025/07/13 23:38:55 jsg Exp $ .\" $NetBSD: profil.2,v 1.3 1995/11/22 23:07:23 cgd Exp $ .\" .\" Copyright (c) 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" Donn Seeley of BSDI. .\" .\" 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. .\" 3. 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. .\" .\" @(#)profil.2 8.1 (Berkeley) 6/4/93 .\" .Dd $Mdocdate: July 13 2025 $ .Dt PROFIL 2 .Os .Sh NAME .Nm profil .Nd control process profiling .Sh SYNOPSIS .In unistd.h .Ft int .Fn profil "void *buf" "size_t buflen" "size_t samplesize" "u_long offset" "u_int scale" "int dirfd" .Sh DESCRIPTION The .Fn profil function is only available inside programs compiled with the .Fl pg compiler / linker option. .Fl pg selects the profiling version of the C-run-time code .Pa ( gcrt0.o ) , which places an ELF note into the binary which enables the system call. The profiling subsystem only works with static binaries, so the .Fl static link option is also required. .Pp The first call to .Fn profil happens at startup inside .Pa gcrt0.o and sets up a region of memory .Fa buf that is .Fa buflen bytes long to contain a .Va struct gmonhdr , a samples buffer of size .Fa samplesize , and a sufficiently-sized arc-table. .Pp .Fa dirfd can indicate the path for placing the output file (environment variable .Ev PROFDIR is the usual choice). Otherwise, \-1 indicates the current (starting) directory location. .Pp Program execution then continues with profiling operational. During execution, profiling can be selectively stopped and restarted using .Xr moncontrol 3 . .Pp While profiling is enabled, at every clock tick, the kernel updates an appropriate count in the samples buffer. .Pp The samples buffer contains .Fa samplesize bytes and is divided into a series of 16-bit bins. Each bin counts the number of times the program counter was in a particular address range in the process when a clock tick occurred while profiling was enabled. For a given program counter address, the number of the corresponding bin is given by the relation: .Bd -literal -offset indent [(pc - offset) / 2] * scale / 65536 .Ed .Pp The .Fa offset parameter is the lowest address at which the kernel takes program counter samples. The .Fa scale parameter ranges from 1 to 65536 and can be used to change the span of the bins. A scale of 65536 maps each bin to 2 bytes of address range; a scale of 32768 gives 4 bytes, 16384 gives 8 bytes and so on. Intermediate values provide approximate intermediate ranges. A .Fa scale value of 0 disables profiling. .Pp At normal program termination, the C-run-time completes the data in the buffer to final format, and proceeds into .Xr _exit 2 . The kernel then constructs a pathname .Pa gmon.progname.pid.out and stores the data to the filesystem (either at the starting directory, or the optional directory indicated by the environment variable .Ev PROFDIR ) . .Pp Further processing is then done using .Xr gprof 1 . .Sh RETURN VALUES .Rv -std .Sh FILES .Bl -tag -width gmon.progname.pid.out -compact .It Pa /usr/lib/gcrt0.o profiling C run-time startup file .It Pa gmon.progname.pid.out conventional name for profiling output file .El .Sh ERRORS The following error may be reported: .Bl -tag -width Er .It Bq Er EPERM The program was not linked with .Fl pg . .It Bq Er EALREADY An attempt was made to change the profile buffer. .It Bq Er EBADF The .Fa dirfd argument is not a valid file descriptor. .It Bq Er ENOTDIR The .Fa dirfd argument does not refer to a directory. .It Bq Er EINVAL The .Fa scale value is too large. .El .Sh SEE ALSO .Xr gprof 1 .Sh HISTORY The .Fn profil system call first appeared in .At v5 . .Pp Historically, profile information was written to the file by the C-run-time exit processing code using .Xr open 2 , .Xr write 2 , and such \(em which is incompatible with modern privilege separation practices like .Xr chroot 2 , .Xr pledge 2 , .Xr setresuid 2 , and .Xr unveil 2 . This replacement .Fn profil interface was redesigned so the kernel writes out the profiling information on behalf of the terminating process. .Sh BUGS The .Fa samples argument should really be a vector of type .Fa "unsigned short" .