man2/cacheflush.2

.\" Written by Ralf Baechle (ralf@waldorf-gmbh.de),
.\" Copyright (c) 1994, 1995 Waldorf GMBH
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, see
.\" <http://www.gnu.org/licenses/>.
.\" %%%LICENSE_END
.\"
.TH CACHEFLUSH 2 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
cacheflush \- flush contents of instruction and/or data cache
.SH SYNOPSIS
.nf
.B #include <sys/cachectl.h>
.PP
.BI "int cacheflush(void *" addr ", int "nbytes ", int "cache );
.fi
.PP
.IR Note :
On some architectures,
there is no glibc wrapper for this system call; see NOTES.
.SH DESCRIPTION
.BR cacheflush ()
flushes the contents of the indicated cache(s) for the
user addresses in the range
.I addr
to
.IR (addr+nbytes\-1) .
.I cache
may be one of:
.TP
.B ICACHE
Flush the instruction cache.
.TP
.B DCACHE
Write back to memory and invalidate the affected valid cache lines.
.TP
.B BCACHE
Same as
.BR (ICACHE|DCACHE) .
.SH RETURN VALUE
.BR cacheflush ()
returns 0 on success.
On error, it returns \-1 and sets
.I errno
to indicate the error.
.SH ERRORS
.TP
.B EFAULT
Some or all of the address range
.I addr
to
.I (addr+nbytes\-1)
is not accessible.
.TP
.B EINVAL
.I cache
is not one of
.BR ICACHE ,
.BR DCACHE ,
or
.BR BCACHE
(but see BUGS).
.SH CONFORMING TO
Historically, this system call was available on all MIPS UNIX variants
including RISC/os, IRIX, Ultrix, NetBSD, OpenBSD, and FreeBSD
(and also on some non-UNIX MIPS operating systems), so that
the existence of this call in MIPS operating systems is a de-facto
standard.
.SS Caveat
.BR cacheflush ()
should not be used in programs intended to be portable.
On Linux, this call first appeared on the MIPS architecture,
but nowadays, Linux provides a
.BR cacheflush ()
system call on some other architectures, but with different arguments.
.SH NOTES
.SS Architecture-specific variants
Glibc provides a wrapper for this system call,
with the prototype shown in SYNOPSIS,
for the following architectures:
ARC, CSKY, MIPS, and NIOS2.
.PP
On some other architectures,
Linux provides this system call, with different arguments:
.TP
M68K:
.nf
.BI "int cacheflush(unsigned long " addr ", int " scope ", int " cache ,
.BI "               unsigned long " len );
.fi
.TP
SH:
.nf
.BI "int cacheflush(unsigned long " addr ", unsigned long " len ", int " op );
.fi
.TP
NDS32:
.nf
.BI "int cacheflush(unsigned int " start ", unsigned int " end ", int " cache );
.fi
.PP
On the above architectures,
glibc does not provide a wrapper for this system call; call it using
.BR syscall (2).
.SS GCC alternative
Unless you need the finer grained control that this system call provides,
you probably want to use the GCC built-in function
.BR __builtin___clear_cache (),
which provides a portable interface
across platforms supported by GCC and compatible compilers:
.PP
.in +4n
.EX
.BI "void __builtin___clear_cache(void *" begin ", void *" end );
.EE
.in
.PP
On platforms that don't require instruction cache flushes,
.BR __builtin___clear_cache ()
has no effect.
.PP
.IR Note :
On some GCC-compatible compilers,
the prototype for this built-in function uses
.I char *
instead of
.I void *
for the parameters.
.SH BUGS
Linux kernels older than version 2.6.11 ignore the
.I addr
and
.I nbytes
arguments, making this function fairly expensive.
Therefore, the whole cache is always flushed.
.PP
This function always behaves as if
.BR BCACHE
has been passed for the
.I cache
argument and does not do any error checking on the
.I cache
argument.