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man pages section 2: System Calls

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Updated: Thursday, June 13, 2019
 
 

mprotect(2)

Name

mprotect - set protection of memory mapping

Synopsis

#include <sys/mman.h>

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

Description

The mprotect() function changes the access protections on the mappings specified by the range [addr, addr + len ), rounding len up to the next multiple of the page size as returned by sysconf(3C), to be that specified by prot. Legitimate values for prot are the same as those permitted for mmap(2) 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 */

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.

Return Values

Upon successful completion, mprotect() returns 0. Otherwise, it returns −1 and sets errno to indicate the error.

Errors

The mprotect() function will fail if:

EACCES

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

There are addresses in the range [addr, addr + len) which are part of a shmget_osm(2) created shared memory segment, and the prot argument would change the permissions of the segment.

EINVAL

The len argument has a value equal to 0, or addr is not a multiple of the page size as returned by sysconf(3C).

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.

The mprotect() function may fail if:

EAGAIN

The address range [addr, addr + len) includes one or more pages that have been locked in memory and that were mapped MAP_PRIVATE; prot includes PROT_WRITE; and the system has insufficient resources to reserve memory for the private pages that may be created. These private pages may be created by store operations in the now-writable address range.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Standard

See Also

mmap(2), mlock(3C), mlockall(3C), plock(3C), sysconf(3C), attributes(7), standards(7)