MMAPOBJ(2)MMAPOBJ(2)NAMEmmapobj - map a file object in the appropriate manner
SYNOPSIS
#include <sys/mman.h>
int mmapobj(int fd, uint_t flags, mmapobj_result_t *storage,
uint_t *elements, void *arg);
PARAMETERS
fd
The open file descriptor for the file to be mapped.
flags
Indicates that the default behavior of mmapobj() should be
modified accordingly. Available flags are:
MMOBJ_INTERPRET
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.
MMOBJ_PADDING
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 for‐
mat.
storage
A pointer to the mmapobj_result_t array where the mapping
data will be copied out after a successful mapping of fd.
elements
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 necessary.
arg
A pointer to additional information that might be associ‐
ated with the specific request. Only the MMOBJ_PADDING
request uses this argument. If MMOBJ_PADDING is not speci‐
fied, arg must be NULL.
DESCRIPTION
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_INTER‐
PRET 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 supported:
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.
ET_REL and ET_CORE
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 com‐
mon 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
begins.
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().
RETURN VALUES
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 mem‐
bers 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.
ERRORS
The mmapobj() function will fail if:
E2BIG
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
required.
EACCES
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.
EADDRINUSE
The mapping requirements overlap an object that is
already used by the process.
EAGAIN
There is insufficient room to reserve swap space for the
mapping.
The file to be mapped is already locked using advisory or
mandatory record locking. See fcntl(2).
EBADF
The fd argument is not a valid open file descriptor.
EFAULT
The storage, arg, or elements argument points to an
invalid address.
EINVAL
The flags argument contains an invalid flag.
MMOBJ_PADDING was not specified in flagsand arg was non-
null.
ENODEV
The fd argument refers to an object for which mmapobj()
is meaningless, such as a terminal.
ENOMEM
Insufficient memory is available to hold the program
headers.
Insufficient memory is available in the address space to
create the mapping.
ENOTSUP
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 ENOT‐
SUP.
The fd argument is a file whose type can not be inter‐
preted and MMOBJ_INTERPRET was specified in flags.
The ELF header contains an unaligned e_phentsize value.
ENOSYS
An unsupported filesystem operation was attempted while
trying to map in the object.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Private │
├────────────────────┼───────────────────┤
│MT-Level │ Async-Signal-Safe │
└────────────────────┴───────────────────┘
SEE ALSOld.so.1(1), fcntl(2), memcntl(2), mmap(2), mprotect(2), munmap(2),
elf(3ELF), madvise(3C), mlockall(3C), msync(3C), a.out(4),
attributes(5)
Linker and Libraries Guide
Dec 1, 2008 MMAPOBJ(2)
