mmapobj

- 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 format.

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 associated with the specific request. Only the MMOBJ_PADDING request uses this argument. If MMOBJ_PADDING is not specified, 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_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 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 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 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 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.

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.

The file to be mapped has a length of 0.

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 ENOTSUP.

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.

ENOSYS

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

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

ld.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)

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