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mprotect(2)							   mprotect(2)

NAME    [Toc]    [Back]

     mprotect -	set protection of memory mapping

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/mman.h>

     int mprotect(void *addr, size_t len, int prot);

DESCRIPTION    [Toc]    [Back]

     The function mprotect changes the access protections on the mappings
     specified by the range [addr, addr	+ len) to be that specified by prot.
     Legitimate	values for prot	are the	same as	those permitted	for mmap and
     are defined in <sys/mman.h> as:

     PROT_READ	     /*	page can be read */
     PROT_WRITE	     /*	page can be written */
     PROT_EXEC	     /*	page can be executed */
     PROT_NONE	     /*	page can not be	accessed */
     PROT_EXEC_NOFLUSH /* page can be executed - cache not synced */

     Not all implementations literally provide all possible combinations.
     PROT_WRITE	is often implemented as	PROT_READ|PROT_WRITE and PROT_EXEC as
     PROT_READ|PROT_EXEC.  This	is true	for all	SGI implementations.  In
     particular, MIPS processors do not	support	a separate execute permission.
     Any page that can be read can be executed from, even if PROT_EXEC is not
     specified.	 As described below, the operating system uses PROT_EXEC as a
     flag to indicate it may need to perform certain platform dependent
     functions that may	be needed to properly execute instructions from	the
     associated	page.  However,	no implementation will permit a	store to
     succeed where PROT_WRITE has not been set.

     Applications such as compiling interpreters that generate code in their
     data areas	and then wish to execute it, should use	mprotect to add
     PROT_EXEC permission to the corresponding pages.  This must be done after
     the code has been generated, but before it	is executed.  This causes any
     necessary machine dependent activities, such as cache flushing, to	occur
     that are required prior to	executing from any part	of the process's
     address space other than the program or library text segments.  If	the
     generated instructions are	altered	after the previous call	to mprotect
     was made to mark the data as executable, then mprotect must be called to
     again add PROT_EXEC before	the new	code is	executed in order to prepare
     the new contents of the page(s) for proper	execution.

     In	some cases, it may be better for performance reasons to	keep execute
     permissions on a page without syncing the instruction and data cache.  In
     these cases, specify PROT_EXEC_NOFLUSH to keep the	cache from being
     flushed.  However,	it is then up to the programmer	to call	mprotect with
     PROT_EXEC to sync the cache when instructions in a	page change.

									Page 1

mprotect(2)							   mprotect(2)

RETURN VALUE    [Toc]    [Back]

     On	success, mprotect returns 0; on	failure, mprotect returns -1 and sets
     errno to indicate an error.

ERRORS    [Toc]    [Back]

     Under the following conditions, the function mprotect fails and sets
     errno to:

     EACCES prot specifies a protection	that violates the access permission
	    the	process	has to the underlying memory object.

     EAGAIN prot specifies PROT_WRITE over a MAP_PRIVATE mapping and there are
	    insufficient memory	resources to reserve for locking the private

     EINVAL addr is not	a multiple of the page size as returned	by sysconf.

     ENOMEM The	argument len has a value less than or equal to 0.

     ENOMEM Addresses in the range [addr, addr + len) are invalid for the
	    address space of a process,	or specify one or more pages which are
	    not	mapped.

     When mprotect fails for reasons other than	EINVAL,	the protections	on
     some of the pages in the range [addr, addr	+ len) may have	been changed.
     If	the error occurs on some page at addr2,	then the protections of	all
     whole pages in the	range [addr, addr2] will have been modified.

SEE ALSO    [Toc]    [Back]

     mmap(2), plock(2),	sysconf(3C)

									PPPPaaaaggggeeee 2222
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 Similar pages
Name OS Title
mprotect HP-UX set or check protection of memory mapping
vm_map_check_protection FreeBSD check memory protection for a vm_map
vm_map_protect FreeBSD apply protection bits to a virtual memory region
mman HP-UX memory mapping definitions
mprotect Tru64 Modify access protections of memory mapping
mprotect NetBSD control the protection of pages
pmap_page_protect FreeBSD set physical page protection
vm_page_protect FreeBSD lower a page's protection
mprotect OpenBSD control the protection of pages
pmap_protect FreeBSD set physical page protection
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