MMAPOBJ(2) System Calls MMAPOBJ(2)


mmapobj - map a file object in the appropriate manner


#include <sys/mman.h>

int mmapobj(int fd, uint_t flags, mmapobj_result_t *storage,
uint_t *elements, void *arg);


The open file descriptor for the file to be mapped.

Indicates that the default behavior of mmapobj() should be
modified accordingly. Available flags are:


Interpret the contents of the file descriptor instead of
just mapping it as a single image. This flag can be used
only with ELF and AOUT files.


When mapping in the file descriptor, add an additional
mapping before the lowest mapping and after the highest
mapping. The size of this padding is at least as large as
the amount pointed to by arg. These mappings will be
private to the process, will not reserve any swap space
and will have no protections. To use this address space,
the protections for it will need to be changed. This
padding request will be ignored for the AOUT format.

A pointer to the mmapobj_result_t array where the mapping
data will be copied out after a successful mapping of fd.

A pointer to the number of mmapobj_result_t elements pointed
to by storage. On return, elements contains the number of
mappings required to fully map the requested object. If the
original value of elements is too small, E2BIG is returned
and elements is modified to contain the number of mappings

A pointer to additional information that might be associated
with the specific request. Only the MMOBJ_PADDING request
uses this argument. If MMOBJ_PADDING is not specified, arg
must be NULL.


The mmapobj() function establishes a set of mappings between a process's
address space and a file. By default, mmapobj() maps the whole file as a
single, private, read-only mapping. The MMOBJ_INTERPRET flag instructs
mmapobj() to attempt to interpret the file and map the file according to
the rules for that file format. The following ELF and AOUT formats are

ET_EXEC and AOUT executables

This format results in one or more mappings whose size, alignment and
protections are as described by the file's program header
information. The address of each mapping is explicitly defined by the
file's program headers.

ET_DYN and AOUT shared objects

This format results in one or more mappings whose size, alignment and
protections are as described by the file's program header
information. The base address of the initial mapping is chosen by
mmapobj(). The addresses of adjacent mappings are based off of this
base address as defined by the file's program headers.


This format results in a single, read-only mapping that covers the
whole file. The base address of this mapping is chosen by mmapobj().

The mmapobj() function will not map over any currently used mappings
within the process, except for the case of an ELF ET_EXEC file for which
a previous reservation has been made via /dev/null. The most common way
to make such a reservation would be with an mmap() of /dev/null.

Mappings created with mmapobj() can be processed individually by other
system calls such as munmap(2).

The mmapobj_result structure contains the following members:

typedef struct mmapobj_result {
caddr_t mr_addr; /* mapping address */
size_t mr_msize; /* mapping size */
size_t mr_fsize; /* file size */
size_t mr_offset; /* offset into file */
uint_t mr_prot; /* the protections provided */
uint_t mr_flags; /* info on the mapping */
} mmapobj_result_t;

The macro MR_GET_TYPE(mr_flags) must be used when looking for the above
flags in the value of mr_flags.

Values for mr_flags include:

MR_PADDING 0x1 /* this mapping represents requested padding */
MR_HDR_ELF 0x2 /* the ELF header is mapped at mr_addr */
MR_HDR_AOU 0x3 /* the AOUT header is mapped at mr_addr */

When MR_PADDING is set, mr_fsize and mr_offset will both be 0.

The mr_fsize member represents the amount of the file that is mapped into
memory with this mapping.

The mr_offset member is the offset into the mapping where valid data

The mr_msize member represents the size of the memory mapping starting at
mr_addr. This size may include unused data prior to mr_offset that exists
to satisfy the alignment requirements of this segment. This size may also
include any non-file data that are required to provide NOBITS data
(typically .bss). The system reserves the right to map more than mr_msize
bytes of memory but only mr_msize bytes will be available to the caller
of mmapobj().


Upon successful completion, 0 is returned and elements contains the
number of program headers that are mapped for fd. The data describing
these elements are copied to storage such that the first elements members
of the storage array contain valid mapping data.

On failure, -1 is returned and errno is set to indicate the error. No
data is copied to storage.


The mmapobj() function will fail if:

The elements argument was not large enough to hold the
number of loadable segments in fd. The elements argument
will be modified to contain the number of segments

The file system containing the fd to be mapped does not
allow execute access, or the file descriptor pointed to by
fd is not open for reading.

The mapping requirements overlap an object that is already
used by the process.

There is insufficient room to reserve swap space for the

The file to be mapped is already locked using advisory or
mandatory record locking. See fcntl(2).

The fd argument is not a valid open file descriptor.

The storage, arg, or elements argument points to an invalid

The flags argument contains an invalid flag.

MMOBJ_PADDING was not specified in flags and arg was non-

The fd argument refers to an object for which mmapobj() is
meaningless, such as a terminal.

Insufficient memory is available to hold the program

Insufficient memory is available in the address space to
create the mapping.

The current user data model does not match the fd to be
interpreted; thus, a 32-bit process that tried to use
mmapobj() to interpret a 64-bit object would return

The fd argument is a file whose type can not be interpreted
and MMOBJ_INTERPRET was specified in flags.

The ELF header contains an unaligned e_phentsize value.

An unsupported filesystem operation was attempted while
trying to map in the object.


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

|Interface Stability | Private |
|MT-Level | Async-Signal-Safe |

SEE ALSO, fcntl(2), memcntl(2), mmap(2), mprotect(2), munmap(2),
madvise(3C), mlockall(3C), msync(3C), elf(3ELF), a.out(5), attributes(7)

Linker and Libraries Guide

illumos June 20, 2021 MMAPOBJ(2)