elf_update man page on SmartOS

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ELF_UPDATE(3ELF)					      ELF_UPDATE(3ELF)

NAME
       elf_update - update an ELF descriptor

SYNOPSIS
       cc [ flag ... ] file ... -lelf [ library ... ]
       #include <libelf.h>

       off_t elf_update(Elf *elf, Elf_Cmd cmd);

DESCRIPTION
       The elf_update() function causes the library to examine the information
       associated with an ELF descriptor, elf, and to recalculate  the	struc‐
       tural data needed to generate the file's image.

       The cmd argument can have the following values:

       ELF_C_NULL
		      This  value  tells  elf_update()	to recalculate various
		      values, updating only the ELF descriptor's memory struc‐
		      tures.  Any  modified  structures	 are  flagged with the
		      ELF_F_DIRTY bit. A program thus can  update  the	struc‐
		      tural information and then reexamine them without chang‐
		      ing the file associated with the ELF descriptor. Because
		      this  does  not  change the file, the ELF descriptor may
		      allow reading, writing, or both reading and writing (see
		      elf_begin(3ELF)).

       ELF_C_WRITE
		      If  cmd  has  this  value,  elf_update()	duplicates its
		      ELF_C_NULL actions and also writes any ``dirty''	infor‐
		      mation  associated  with the ELF descriptor to the file.
		      That is, when a program has  used	 elf_getdata(3ELF)  or
		      the  elf_flagdata(3ELF)  facilities  to  supply  new (or
		      update existing)	information  for  an  ELF  descriptor,
		      those  data will be examined, coordinated, translated if
		      necessary (see elf32_xlatetof(3ELF)), and written to the
		      file.  When  portions  of	 the  file  are	 written,  any
		      ELF_F_DIRTY bits are reset, indicating  those  items  no
		      longer  need  to	be  written to the file (see elf_flag‐
		      data(3ELF)). The sections' data are written in the order
		      of  their section header entries, and the section header
		      table is written to the end of the file.	When  the  ELF
		      descriptor  was  created	with elf_begin(), it must have
		      allowed writing the file. That is, the elf_begin()  com‐
		      mand must have been either ELF_C_RDWR or ELF_C_WRITE.

       If  elf_update()	 succeeds, it returns the total size of the file image
       (not the memory image), in bytes. Otherwise an error occurred, and  the
       function returns −1.

       When  updating  the internal structures, elf_update() sets some members
       itself. Members listed below are the application's  responsibility  and
       retain the values given by the program.

       The following table shows ELF Header members:

       Member		  Notes

       e_ident[EI_DATA]	  Library controls other e_ident values
       e_type
       e_machine
       e_version
       e_entry
       e_phoff		  Only when ELF_F_LAYOUT asserted
       e_shoff		  Only when ELF_F_LAYOUT asserted
       e_flags
       e_shstrndx

       The following table shows the Program Header members:

       Member	  Notes

       p_type	  The application controls all
       p_offset	  program header entries
       p_vaddr
       p_paddr
       p_filesz
       p_memsz
       p_flags
       p_align

       The following table shows the Section Header members:

       Member	      Notes

       sh_name
       sh_type
       sh_flags
       sh_addr
       sh_offset      Only when ELF_F_LAYOUT asserted
       sh_size	      Only when ELF_F_LAYOUT asserted
       sh_link
       sh_info
       sh_addralign   Only when ELF_F_LAYOUT asserted
       sh_entsize

       The following table shows the Data Descriptor members:

       Member	   Notes

       d_buf
       d_type

       d_size
       d_off	   Only when ELF_F_LAYOUT asserted
       d_align
       d_version

       Note  that  the	program	 is responsible for two particularly important
       members (among others) in the ELF header. The e_version member controls
       the  version  of data structures written to the file. If the version is
       EV_NONE,	  the	library	  uses	 its   own   internal	version.   The
       e_ident[EI_DATA]	 entry controls the data encoding used in the file. As
       a special case, the value may be ELFDATANONE to request the native data
       encoding	 for  the  host	 machine.  An error occurs in this case if the
       native encoding doesn't match a file encoding known by the library.

       Further note that the program is responsible for the sh_entsize section
       header  member.	Although  the  library sets it for sections with known
       types, it cannot reliably know the correct value for all sections. Con‐
       sequently,  the library relies on the program to provide the values for
       unknown section types.  If the entry size is unknown or not applicable,
       the value should be set to 0.

       When  deciding  how  to	build  the output file, elf_update() obeys the
       alignments of individual data buffers to create output sections. A sec‐
       tion's  most strictly aligned data buffer controls the section's align‐
       ment. The library also inserts padding between buffers,	as  necessary,
       to ensure the proper alignment of each buffer.

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

       ┌────────────────────┬─────────────────┐
       │  ATTRIBUTE TYPE    │ ATTRIBUTE VALUE │
       ├────────────────────┼─────────────────┤
       │Interface Stability │ Stable	      │
       ├────────────────────┼─────────────────┤
       │MT-Level	    │ MT-Safe	      │
       └────────────────────┴─────────────────┘

SEE ALSO
       elf(3ELF), elf32_fsize(3ELF), elf32_getehdr(3ELF), elf32_getshdr(3ELF),
       elf32_xlatetof(3ELF),  elf_begin(3ELF),	elf_flagdata(3ELF),   elf_get‐
       data(3ELF), libelf(3LIB), attributes(5)

NOTES
       As  mentioned  above, the ELF_C_WRITE command translates data as neces‐
       sary, before writing them to the file. This translation is  not	always
       transparent  to	the  application  program.  If	a program has obtained
       pointers to data associated with a file (for example,  see  elf32_gete‐
       hdr(3ELF)  and  elf_getdata(3ELF)),  the program should reestablish the
       pointers after calling elf_update().

				 Jul 11, 2001		      ELF_UPDATE(3ELF)
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