man2/cacheflush.2

   1 .\" Written by Ralf Baechle (ralf@waldorf-gmbh.de),
   2 .\" Copyright (c) 1994, 1995 Waldorf GMBH
   3 .\"
   4 .\" SPDX-License-Identifier: GPL-2.0-or-later
   5 .\"
   6 .TH CACHEFLUSH 2 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   7 .SH NAME
   8 cacheflush \- flush contents of instruction and/or data cache
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <sys/cachectl.h>
  15 .PP
  16 .BI "int cacheflush(void *" addr ", int "nbytes ", int "cache );
  17 .fi
  18 .PP
  19 .IR Note :
  20 On some architectures,
  21 there is no glibc wrapper for this system call; see NOTES.
  22 .SH DESCRIPTION
  23 .BR cacheflush ()
  24 flushes the contents of the indicated cache(s) for the
  25 user addresses in the range
  26 .I addr
  27 to
  28 .IR (addr+nbytes\-1) .
  29 .I cache
  30 may be one of:
  31 .TP
  32 .B ICACHE
  33 Flush the instruction cache.
  34 .TP
  35 .B DCACHE
  36 Write back to memory and invalidate the affected valid cache lines.
  37 .TP
  38 .B BCACHE
  39 Same as
  40 .BR (ICACHE|DCACHE) .
  41 .SH RETURN VALUE
  42 .BR cacheflush ()
  43 returns 0 on success.
  44 On error, it returns \-1 and sets
  45 .I errno
  46 to indicate the error.
  47 .SH ERRORS
  48 .TP
  49 .B EFAULT
  50 Some or all of the address range
  51 .I addr
  52 to
  53 .I (addr+nbytes\-1)
  54 is not accessible.
  55 .TP
  56 .B EINVAL
  57 .I cache
  58 is not one of
  59 .BR ICACHE ,
  60 .BR DCACHE ,
  61 or
  62 .B BCACHE
  63 (but see BUGS).
  64 .SH STANDARDS
  65 Historically, this system call was available on all MIPS UNIX variants
  66 including RISC/os, IRIX, Ultrix, NetBSD, OpenBSD, and FreeBSD
  67 (and also on some non-UNIX MIPS operating systems), so that
  68 the existence of this call in MIPS operating systems is a de-facto
  69 standard.
  70 .SS Caveat
  71 .BR cacheflush ()
  72 should not be used in programs intended to be portable.
  73 On Linux, this call first appeared on the MIPS architecture,
  74 but nowadays, Linux provides a
  75 .BR cacheflush ()
  76 system call on some other architectures, but with different arguments.
  77 .SH NOTES
  78 .SS Architecture-specific variants
  79 Glibc provides a wrapper for this system call,
  80 with the prototype shown in SYNOPSIS,
  81 for the following architectures:
  82 ARC, CSKY, MIPS, and NIOS2.
  83 .PP
  84 On some other architectures,
  85 Linux provides this system call, with different arguments:
  86 .TP
  87 M68K:
  88 .nf
  89 .BI "int cacheflush(unsigned long " addr ", int " scope ", int " cache ,
  90 .BI "               unsigned long " len );
  91 .fi
  92 .TP
  93 SH:
  94 .nf
  95 .BI "int cacheflush(unsigned long " addr ", unsigned long " len ", int " op );
  96 .fi
  97 .TP
  98 NDS32:
  99 .nf
 100 .BI "int cacheflush(unsigned int " start ", unsigned int " end ", int " cache );
 101 .fi
 102 .PP
 103 On the above architectures,
 104 glibc does not provide a wrapper for this system call; call it using
 105 .BR syscall (2).
 106 .SS GCC alternative
 107 Unless you need the finer grained control that this system call provides,
 108 you probably want to use the GCC built-in function
 109 .BR __builtin___clear_cache (),
 110 which provides a portable interface
 111 across platforms supported by GCC and compatible compilers:
 112 .PP
 113 .in +4n
 114 .EX
 115 .BI "void __builtin___clear_cache(void *" begin ", void *" end );
 116 .EE
 117 .in
 118 .PP
 119 On platforms that don't require instruction cache flushes,
 120 .BR __builtin___clear_cache ()
 121 has no effect.
 122 .PP
 123 .IR Note :
 124 On some GCC-compatible compilers,
 125 the prototype for this built-in function uses
 126 .I char *
 127 instead of
 128 .I void *
 129 for the parameters.
 130 .SH BUGS
 131 Linux kernels older than version 2.6.11 ignore the
 132 .I addr
 133 and
 134 .I nbytes
 135 arguments, making this function fairly expensive.
 136 Therefore, the whole cache is always flushed.
 137 .PP
 138 This function always behaves as if
 139 .B BCACHE
 140 has been passed for the
 141 .I cache
 142 argument and does not do any error checking on the
 143 .I cache
 144 argument.