ELF_UPDATE(3) BSD Library Functions Manual ELF_UPDATE(3)
elf_update -- update an ELF descriptor
ELF Access Library (libelf, -lelf)
elf_update(Elf *elf, Elf_Cmd cmd);
Function elf_update() causes the library to recalculate the structure of an ELF object and optionally write out the image of the object to
Argument elf is a descriptor to an ELF object. Argument cmd can take on the following values:
ELF_C_NULL The library will recalculate structural information flagging modified structures with the ELF_F_DIRTY flag, but will not write
back data to the underlying file image.
ELF_C_WRITE The library will recalculate structural information and will also write the new image to the underlying file.
If the ELF_F_LAYOUT flag has been set on the ELF descriptor, the application assumes full responsibility for the layout of the ELF object.
If this flag is not set, the ELF library will compute the layout of the file from its associated section descriptors.
It is the application's responsibility to manage the the following structure members in the ELF file:
The ELF executable header is described in elf(5). The following members of the ELF executable header are the application's responsi-
e_entry Set to the desired entry address for executables.
e_flags Set to the desired processor specific flags.
e_ident[EI_DATA] Must be set to one of ELFDATA2LSB or ELFDATA2MSB.
e_ident[EI_OSABI] Set to the OS ABI desired. For FreeBSD executables, this field should be set to ELFOSABI_FREEBSD.
e_machine Set to the desired machine architecture, one of the EM_* values in <sys/elf_common.h>.
e_phoff If the application is managing the object's layout, it must set this field to the file offset of the ELF program
e_shoff If the application is managing the object's layout, it must set this field to the file offset of the ELF section
e_shstrndx Set to the index of the string table containing section names.
e_type Set to the type of the ELF object, one of the ET_* values in <sys/elf_common.h>.
e_version Set to the desired version of the ELF object.
All fields of the entries in the program header table are under application control.
The ELF section header is described in elf(5). The following members of the ELF section header are the application's responsibility:
sh_addr Set to the physical memory address where the section should reside.
sh_addralign If the application is managing the file layout, it must set this field to the desired alignment for the section's con-
tents. This value must be a power of two.
sh_entsize Set to the size of each entry, for sections containing fixed size elements, or set to zero for sections without fixed
size elements. If the application is not managing file layout, it may leave this field as zero for those sections
whose types known to the library.
sh_flags Set to the desired section flags.
sh_info Set as described in elf(5).
sh_link Set as described in elf(5).
sh_name Set to the index of the section's name in the string table containing section names.
sh_offset If the application is managing the file layout, it must set this field to the file offset of the section's contents.
sh_size If the application is managing the file layout, it must set this field to the file size of the section's contents.
sh_type Set to the type of the section.
Gaps in the coverage of the file's contents will be set to the fill value specified by elf_fill(3).
If the application has requested full control over the file's layout by setting the ELF_F_LAYOUT flag on the ELF descriptor, it should ensure
that there are no gaps in the coverage of the file's contents.
All pointers to Elf_Scn and Elf_Data descriptors associated with descriptor elf should be considered as invalid after a call to elf_update().
Function elf_update() returns the total size of the file image if successful, or -1 if an error occurred.
This function may fail with the following errors:
[ELF_E_ARGUMENT] Argument elf was null.
[ELF_E_ARGUMENT] Argument cmd was not recognized.
[ELF_E_ARGUMENT] The argument elf was not a descriptor for an ELF object.
[ELF_E_CLASS] The e_ident[EI_CLASS] field of the executable header of argument elf did not match the class of the file.
[ELF_E_DATA] An Elf_Data descriptor contained in argument elf specified a type incompatible with its containing section.
[ELF_E_HEADER] The ELF header in argument elf requested a different byte order from the byte order already associated with the file.
[ELF_E_IO] An I/O error was encountered.
[ELF_E_LAYOUT] An Elf_Data descriptor contained in argument elf specified an alignment incompatible with its containing section.
[ELF_E_LAYOUT] Argument elf contained section descriptors that overlapped in extent.
[ELF_E_LAYOUT] Argument elf contained section descriptors that were incorrectly aligned or were too small for their data.
[ELF_E_LAYOUT] The flag ELF_F_LAYOUT was set on the Elf descriptor and the section header table overlapped an extent in the object mapped
by a section descriptor.
[ELF_E_MODE] An ELF_C_WRITE operation was requested with an ELF descriptor that was not opened for writing or updating.
[ELF_E_SECTION] Argument elf contained a section with an unrecognized type.
[ELF_E_SECTION] The section header at index SHN_UNDEF had an illegal section type.
[ELF_E_SEQUENCE] An ELF_C_WRITE operation was requested after a prior call to elf_cntl(elf, ELF_C_FDDONE) disassociated the ELF descriptor
elf from its underlying file.
[ELF_E_VERSION] Argument elf had an unsupported version or contained an Elf_Data descriptor with an unsupported version.
elf(3), elf32_getehdr(3), elf32_getphdr(3), elf32_newehdr(3), elf32_newphdr(3), elf64_getehdr(3), elf64_getphdr(3), elf64_newehdr(3),
elf64_newphdr(3), elf_cntl(3), elf_fill(3), elf_flagehdr(3), elf_flagelf(3), elf_getdata(3), elf_getscn(3), elf_newdata(3), elf_newscn(3),
elf_rawdata(3), gelf(3), gelf_newehdr(3), gelf_newphdr(3), elf(5)
March 19, 2008 BSD