cacheflush (2) - Linux Manuals

cacheflush: flush contents of instruction and/or data cache

Command to display cacheflush manual in Linux: $ man 2 cacheflush

NAME

cacheflush - flush contents of instruction and/or data cache

SYNOPSIS

#include <asm/cachectl.h>

int cacheflush(char *addr, int nbytes, int cache);

Note: On some architectures, there is no glibc wrapper for this system call; see NOTES.

DESCRIPTION

cacheflush() flushes the contents of the indicated cache(s) for the user addresses in the range addr to (addr+nbytes-1). cache may be one of:

ICACHE: Flush the instruction cache.
DCACHE: Write back to memory and invalidate the affected valid cache lines.
BCACHE: Same as (ICACHE|DCACHE).

RETURN VALUE

cacheflush() returns 0 on success or -1 on error. If errors are detected, errno will indicate the error.

ERRORS

EFAULT: Some or all of the address range addr to (addr+nbytes-1) is not accessible.
EINVAL: cache is not one of ICACHE, DCACHE, or BCACHE (but see BUGS).

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.

Caveat

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 cacheflush() system call on some other architectures, but with different arguments.

NOTES

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.

On some other architectures, Linux provides this system call, with different arguments:

M68K:

int cacheflush(unsigned long addr, int scope, int cache,
               unsigned long len);

SH:

int cacheflush(unsigned long addr, unsigned long len, int op);

NDS32:

int cacheflush(unsigned int start, unsigned int end, int cache);

On the above architectures, glibc does not provide a wrapper for this system call; call it using syscall(2).

GCC alternative

Unless you need the finer grained control that this system call provides, you probably want to use the GCC built-in function __builtin___clear_cache(), which provides a portable interface across platforms supported by GCC and compatible compilers:

void __builtin___clear_cache(void *begin, void *end);

On platforms that don't require instruction cache flushes, __builtin___clear_cache() has no effect.

Note: On some GCC-compatible compilers, the prototype for this built-in function uses char * instead of void * for the parameters.

BUGS

Linux kernels older than version 2.6.11 ignore the addr and nbytes arguments, making this function fairly expensive. Therefore, the whole cache is always flushed.

This function always behaves as if BCACHE has been passed for the cache argument and does not do any error checking on the cache argument.

COLOPHON

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